Nematode Behaviour by Randy Gaugler, Anwar L. Bilgrami (CABI Publishing) Netamode worms are among the most ubiquitous organisms on earth. They include free-living forms as well as parasites of plants, insects, humans and other animals. Netamode behavior is a key issue in understanding of these ways of life or parasitic relationships. This book provides a unique, comprehensive review of current knowledge of the behavior of netamodes. All of the key topics such as locomotion and orientation, feeding and reproductive behavior, and biotic and abiotic interactions are reviewed. Written by leading authorities from the USA, UK, India and New Zealand, it brings together a wide range of disciplines and will attract a broad readership.
In the absence of well-defined criteria, behavioural classification of nematodes based upon their activities and adaptations becomes a difficult task. At what point do nematodes sense physical and chemical stimuli? Is the ingestion of food by nematodes passive or active? What type of behaviour do nematodes show when sperm are released? Many similar questions could be addressed if a classification system of nematode activity based on endogenous and exogenous, and biotic and abiotic components was adopted.
Nematodes display behaviours as coordinated and interacted responses. This is why behaviour in such deceptively simple organisms as nematodes is complex. Nematodes use receptors, the central nervous system, and somatic musculature to perform exogenous activities (e.g. locomotion), whereas the sympathetic nervous system, changes in body turgor pressure and somatic muscles are used to accomplish endogenous activities, such as ingestion and defaecation.
Behaviours may be classified into two basic types: operational (voluntary) and consequential (influenced by stimuli). Behaviour by operation refers to what nematodes do and describes exogenous or endogenous activities such as movement, hatching, vulval contractions, stylet movement, etc. Classification by operation brings behavioural patterns of similar spatio-temporal organizations into a single group, including body postures, wave patterns, movements in egg, muscular movements during defecation, swarming, nictation, orientation and penetration. It is simple in some cases (e.g. determining the number of muscles involved in coordinating a particular activity) but difficult where patterns are mixed and complicated, for instance, the different movements involved in single types of behaviour such as orientation, feeding or copulation. Various subcomponents such as crawling, forward and backward movements, coiling, sideways movements, lateral head movements, and head and tail movements may be considered to simplify such classification.
Behaviour by consequence is extremely varied, since nematodes are governed by various endogenous activities and sensory stimuli of physical and chemical natures. Changes in behaviour due to chemical (e.g. kairomones, allomones, sex pheromones) or physical (e.g. temperature, moisture, electricity, evasive actions taken to avoid predation) stimuli are examples of behaviour by consequence. Description of behaviour by consequence brings clarity in experiments, distinguishes different types and reduces experimental error. Behaviour by consequence can take several forms. First, chemical and physical stimuli are information-generating patterns (e.g. movement patterns). Next, modes of triggering stimuli and actions of the nervous system constitute muscular, neurological, and/or physiological mechanisms. These mechanisms present displays which constitute behaviours.
Information on behavioural adaptations to diverse ecological conditions is assembled and discussed by Gregor Yeates in Chapter 1 ('Behavioural and Ecological
Adaptations'). The author has analysed the significance of ongoing adaptive processes with reference to nematode behaviour. Nematodes are classified depending upon their adaptations. For example, Yeates considers marine, freshwater or phreatic nematodes that inhabit permanently water-saturated habitats as interstitial nematodes. Conversely, nematodes using meniscus forces directly for efficient loco-motion, and indirectly benefiting from the more rapid gaseous exchange of thin films, are classified as pellicole nematodes. Diversity in nematode assemblages is dis-cussed over a wide range of habitats with particular reference to adaptation. Behavioural adaptations are apparent in cephalic specialization, body length, number of juvenile stages (Yeates and Boag, 2002), differences in geographical distribution (Bloemers et al., 1997), migration and aggregation (Moens et al., 1999), tolerance to environmental stress (Jacquiet et al., 1996), etc.
Locomotion is fundamental to nematode behaviour and impacts feeding, food finding, mating and migration. Nematodes move by undulatory propulsions as described in detail by Burr and Gans (1998) and Alexander (2002). Locomotion includes crawling or swimming through leaf surfaces, stomata, root hairs and tissues, rotting plant matter, water, excreta, intestinal microvilli, animal tissues, blood vessels and insect tracheae. Nematodes may also accelerate, stop, reverse, turn, omega-turn, probe, orient, swim, burrow, penetrate, poke, lace, climb, bridge, roll, graze, cruise, nictate, aggregate, swarm, ambush, hitchhike, loop or somersault. Although nematodes cannot fly, infective juveniles of some entomopathogenic species nearly accomplish this feat by leaping distances of nine body lengths when in the presence of an insect host. These fascinating aspects of nematode locomotion are explored by Jay Burr and Forest Robinson in Chapter 2 (`Locomotion Behaviour'). This chapter details the various types of loco-motion, the role of the hydrostatic skeleton and neuromuscular control in locomotion. The authors explain how movements are achieved and controlled, how propulsive forces are generated against external substrates, what role neuromuscular system plays, how locomotion is adapted in different environments, and what alternate means are involved in locomotion when undulatory propulsion is absent. The authors elucidate functions of neuromuscular structures associated with nematode locomotion. They discuss the fine points of body wall structure, elastic properties, lateral connection to cuticle, tonus and development of bending muscles. Transmission of forces during locomotion, the functions of synapses, neurotransmitters, and neuromodulators, the propagation of waves, the mechanism of orientation and factors generating frictional resistance are discussed. The authors emphasize the need to study mechanical properties and putative functions of the hydrostatic skeleton, inflation pressures, change in dimensions, crossing angle, elasticity, cuticle ultrastructure and bending. There is a strong need for more integrative investigations on locomotion based on comparative structural, functional and behavioural diversities with reference to nematode adaptations. Of special interest is the promise of novel methodologies, particularly video capture and editing (VCE) with microscopy (De Ley and Bert, 2002) to archive nematode locomotion for in-depth analysis of the mechanisms involved.
Nematodes receive and interpret signals from the environment and from each
other that allow them to find hosts, mates, develop and survive. Ekaterina Riga uses Chapter 3 ('Orientation Behaviour') to describe various facets of nematode orientation behaviour by discussing types of stimuli and mechanisms involved in nematode chemo-, mechano-, photo-, thigmo- and thermo-tactic responses. The functional aspects of receptors are discussed in relation to their role in orientation. Riga suggests that novel control methodologies could develop by disrupting certain phases of the nematode life cycle (e.g. phases during search for food or mates) (Perry, 1994). As hypothesized by Bone and Shorey (1977), such disruptions might be achievable by saturating the nematode's soil environment with artificial pheromones or host cues. Bone (1987) and Perry (1994) have specifically suggested that nematode reproduction could be disrupted using the sex pheromone confusant method. Further studies are needed to understand the role and functions of receptors in nematode orientation.
Comprehensive knowledge about food and feeding habits is fundamental to understanding aetiology. Anwar Bilgrami and Randy Gaugler's Chapter 4 ('Feeding Behaviour') focuses on patterns of feeding types and mechanisms, muscular movements, food and feeding habits, extracorporeal digestion, host recognition, host tissue penetration, prey catching, cannibalism, ingestion and defecation. A central theme is that despite remarkable structural and functional similarities, nematodes show great diversity in food and feeding habits, obtaining nutrients from bacteria, protozoa, fungi, algae, other nematodes, or plant and animal tissues. They may be monophagous or polyphagous with some species even showing dual or biphasic feeding habits (Yeates et al., 1993), switching food resources at different stages of the life cycle. This diversity, coupled with the disparate nature of the disciplines that work with plant, animal, insect and free-living nematodes, has complicated nematode characterization into different feeding groups.
The structure of feeding organs predicts a nematode's food and feeding habits (Bird and Bird, 1991). These structures may differ between nematode groups but they perform the same functions of feeding and ingestion. The feeding apparatus can be categorized into engulfing (e.g. predatory mononchs), piercing (e.g. plant-parasitic, predatory and fungal feeding), cutting (e.g. predatory diplogasterids, some marine and animal-parasitic nematodes) and sucking types (e.g. bacterial feeding and some animal-parasitic nematodes). Plant and fungal feeders and some predatory nematodes possess a needle-like stylet for piercing tissues. Plant-parasitic triplonchids and predatory nygolaims wield a solid pointed tooth, whereas preda-tory mononchs, diplogasterids and monohysterids have buccal cavities with wide openings and specialized structures such as dorsal tooth, ventral teeth and denticles. The subventral lancet, cutting plates, dorsal gutter and dorsal cone are structures associated with animal-parasitic nematode feeding. These structures perform similar functions, i.e. piercing, penetration, cutting food resource and ingestion of nutrients.
Feeding mechanisms vary with the type of nematode feeding apparatus and habitats. Food capture and feeding mechanisms of plant-parasitic (Doncaster and Seymour, 1973), predatory (Bilgrami, 1992, 1993, 1997), insect-parasitic (Grewal et al., 1993; Bilgrami et al., 2001), and microbivore nematodes (Avery and Horvitz,
1990) are reviewed by Bilgrami and Gaugler in Chapter 4. The authors divide nematode feeding into six major components – structure and function of feeding apparatus, feeding types, food search, food capture, post-feeding activities and food preference – by adopting a scheme of classification based on nematode food and feeding habits. Explanations on the role of extracorporeal digestion of nutrients prior to ingestion, formation of tubes and plugs during feeding, and extra-intestinal food absorption provide a better understanding of adaptive processes during nematode feeding.
There is greater variation in nematode reproductive biology than any other aspect of their behaviour. Robin Huettel discusses this diversity in Chapter 5 ('Reproductive Behaviour'), including evolutionary and ecological aspects. How nematodes respond to sex pheromones and what behavioural mechanisms are adopted during mating are among the subjects treated. Sensory habituation, influence of age, sexual status, physical and chemical factors on orientation, recognition and copulation are also considered. Sex pheromone activity in Heterodera glycines females has been attributed to vanillic acid (Jaffe et al., 1989). Bioassays such as lactin binding are used to study chemotactic responses of H schachtii males to female sex pheromones (Aumann et al., 1998). Aumann and Hashem (1993) extracted attractive substances from females of H. schachtii which possess pheromone activity for males. Greet and Perry (1992) reviewed patterns and evolution of sexuality, genetic basis of sex determination, sexual behaviour and differentiation, the role of sex attractants, spicule function and copulation behaviour in nematodes. The cellular basis of chemotaxis, thermotaxis and developmental switching may be studied in nematodes by killing selected neurones with laser ablation and assaying effects on behaviour. Ablation is a powerful but underutilized tool that may be applied to study diverse functions of the nervous system and the cellular basis of specific nematode behaviours.
Ageing has been defined as a time-dependent series of cumulative, progressive, intrinsic and deleterious functional and structural changes that begin to manifest at reproductive maturity, eventually culminating in death (Arking, 1999). Ageing affects locomotion, fecundity, oviposition, vulval contractions, sexual attraction, copulation, osmotic fragility and feeding activities of nematodes (Zuckerman et al., 1972; Gems, 2002; Herndon et al., 2002). Ed Lewis and E.E. Pèrèz in Chapter 6 (Ageing and Developmental Behaviour') describe age-dependent nematode behaviour during development and after reaching adulthood. Learning processes in nematodes are non-associative but are involved in the modification of behaviour due to repeated exposure to a single or multiple cues, e.g. habituation and sensitization (Bernhard and van der Kooy, 2000). Chapter 6 is made more interesting when the authors explain learning processes in nematodes and correlate this with ageing. Our understanding of ageing behaviour has made a deep breach at the genetic and molecular levels using C. elegans as a model organism (Gershon and Gershon, 2001). However, studies on ageing behaviour of other groups of nematodes have been neglected. In this chapter, the authors suggest several lines of research on ageing behaviour in other important nematode species based upon accomplishments with C. elegans. These could prove useful in the development of novel management practices, and in monitoring environmental pollution using nematode behavioural parameters as bioindicators.
Denis Wright brings together the scattered information on behaviour as it relates to waste and ionic regulation in free-living and parasitic nematodes in Chapter 7 (`Osmoregulatory and Excretory Behaviour'). Earlier reviews emphasized the molecular cell biology of animal-parasitic species (Thompson and Geary, 2002). Nematodes regulate water content to adapt to changing osmotic conditions (Wright, 1998). Failure to do so may disrupt locomotion because of the anisometric nature of the cuticle (Wright and Newall, 1980). Osmotic factors also govern nematode survival (Glazer and Salame, 2000), freezing tolerance (Wharton and To, 1996), hatching (Perry, 1986), reproduction (Gysels and Tavernier-Bracke, 1975) and feeding (Raispere, 1989). The nematode excretory system has been described as a `secretory—excretory' system (Wright, 1998) because of its dual role in osmoregulation and excretion. Chapter 7 integrates the two mechanisms so as to explain changes in nematode behaviour occurring due to osmotic stresses and excretion of nitrogenous waste products.
Behavioural responses are the result of intrinsic and extrinsic stimulations involving various physiological and biochemical activities. Roland Perry and Aaron Maule in Chapter 8 (`Physiological and Biochemical Basis of Behaviour') describe how these activities play a huge role in regulating nematode behavioural responses. Physiology and biochemistry influence functions of sense organs, cuticle, muscles, glands, digestive and excretory organs associated with nematode behaviours. Correlations with physiological and biochemical factors have been established with sensory responses (Perry and Aumann, 1998), female sex pheromones (Aumann et al., 1998) and starvation in nematodes (Reversat, 1981). Results on chemosensory responses suggest each receptor cell in the amphids detects different chemicals. A promising approach to investigate chemosensory responses would be to identify and analyse attractants and repellents in the natural environment, and test them for independence. Chapter 8 further describes the role of hormones and enzymes during behaviour including ecdysis, extracorporeal digestion, salivation, hunger, chemoattraction, nerve conduction, dauer formation, population regulation and sex attraction. Chemical neurotransmitters play an important role in nematode behaviour (Sulston et al., 1975; Wright and Awan, 1976). Willet et al. (1980) considered the nervous system in nematodes as cholinergic, with acetylcholine and y-aminobutyric acid as excitatory and inhibitory transmitters respectively. Vaginal and vulval movement in C. elegans, Aphelenchus avenae and Panagrellus redivivus are controlled by serotonin, 5 hydroxytryptophan and adrenaline (Croll, 1975). It is not difficult to study nematode behaviour in relation to neurones as their numbers do not exceed 250 (Willet et al., 1980). Neurones that mediate behavioural responses to different chemicals have been identified through laser ablation (Troemel, 1999). Genetic and molecular studies on nematode behaviour have indicated involvement of G protein signalling pathways in chemotransduction. Nematodes (e.g. C. elegans) are estimated to use approximately 500 chemosensory receptors to detect a large spectrum of chemicals in the environment. Unfortunately, the physiological and biochemical bases of nematode behaviour are
less developed than the rapidly expanding knowledge on the molecular aspects of behaviour, yet Chapter 8 takes a molecular approach to securing a broader perspective on biochemical and physiological aspects of nematode behaviour.
Genes control behaviour and molecular genetics has become a powerful new tool to study nematode behaviour. Maureen Barr and Jinghua Hu in Chapter 9 (Molecular Basis for Behaviour') make a novel effort to describe various aspects of behaviour at the molecular level using C. elegans as their model. Laser ablation experiments have revealed important similarities in C. elegans with visual and olfactory transductions in vertebrates (Mori and Ohshima, 1997). Movement and migration have been analysed theoretically (Anderson et al., 1997a) and experimentally (Anderson et al., 1997b). The role of ageing, acetylcholinesterase, motor neurone M3 and genes in regulating C. elegans behaviour has been established. Studies on neural G protein signals show that EGL-10, RGS-1 and RGS-10 pro-teins alter signals in C. elegans to induce nematode behavioural responses. Oviposition is regulated by the FLP-1 peptide (Waggoner et al., 2000) and reversals in foraging movements are controlled by small subsets of neurones (Zheng et al., 1999).
Most nematodes live in the soil, an environment heavily colonized by other organisms. Nematodes interact with this biotic community and adapt to survive, adaptations that often have behavioural components. How nematodes interact with beneficial and antagonistic organisms including intraspecific interactions, what causes interactions to occur, and how these interactions affect nematode behaviour constitute the subject of Chapter 10 (Biotic Interactions') by Patricia Timper and Keith Davies. This chapter describes different types of interactions, e.g. phoresy, antagonism, mutualism, commensalism and amensalism, with reference to behaviour. The authors draw particular attention to the extraordinary behaviours shown by nematodes in phoretic associations. Phoretic hosts provide transport to fresh resources and protection from unfavourable biotic and abiotic environments. Many species of Rhabditida, Diplogasterida and Aphelenchida develop phoretic relation-ships but few species of Tylenchida (Massey, 1974) and Strongylida are phoretic (Robinson, 1962). Formation of dauer juveniles (Sudhaus, 1976; Maggenti, 1981) and the ability to nictate are a few examples of phoretic adaptations discussed in this chapter. Such interactions are either facultative (e.g. synchronization of Bursaphelenchus seani with helictid wasps, Giblin and Kaya, 1983) or obligate (e.g. synchronization of Bursaphelenchus cocophilus with Rhynchophorus, Giblin-Davis, 1993) depending upon behavioural adaptations. Antagonism, a varied but interactive behaviour leading to nematode predation and parasitism, is discussed in association with important natural enemies such as fungi, bacteria, insects and nematodes (Stirling, 1991). Chapter 10 indicates that competition is the basis for nematode responses such as co-existence, population fluctuation, migration, spatial displacement, aggregation and sharing food resources.
Abiotic factors including temperature, microwaves, electromagnetic waves, radiation, gravity, pH and water potential (Sambongi et al., 2000; Saunders et al., 2000; Soriano et al., 2000; de Pomerai et al., 2002) also influence nematode behaviour and have been studied with special intensity. Chapter 11 (`Abiotic Factors') by
Mary Barbercheck and Larry Duncan reviews nematode responses to these chemical and physical challenges with emphasis on updating and expanding topics treated by Croll (1970). The influence of many abiotic factors on nematode activities has adaptive significance, as these influences elicit responses such as acclimation and orientation. The reasons why such adaptations are necessary in nematodes exposed to adverse physical conditions are discussed. The authors emphasize that nematode sensitivity, tolerance and response to the abiotic environment are keys to exploiting nematode behaviour for the management of economically important species.
Gregorich et al. (2001) defined population dynamics as `the numerical changes in population within a period of time,' whereas Lawrence (1995) described it as `changes in population structure over a period of time'. The former encompasses seasonal variations in nematode populations (Kendall and Bluckland, 1971) whereas the latter includes population cycles (Goodman and Payne, 1979). Chapter 12 (Population Dynamics'), contributed by Brian Boag and Gregor Yeates, reflects both components in an expansive examination of behaviour at the nematode population rather than at the individual level by focusing on temporal and spatial pat-terns of migration. The authors explain non-uniform distribution behaviour of nematodes in soils, sediments, and plant and animal tissues. They also describe changes in behaviour during migration and environmental conditions responsible for variations in populations and migrations. For example, variation in vertical migratory behaviour (Boag, 1981) is attributed to root distribution, soil type, moisture, temperature, etc. (Yeates, 1980; Rawsthorne and Brodie, 1986; Young et al., 1998). Horizontal migratory behaviour is suggested (Taylor, 1979) as a useful tool to detect and estimate the size of nematode populations (Been and Schomaker, 1996), as well as mechanisms of nematode aggregation (Goodell and Ferris, 1981). Migratory behaviour deserves special attention with reference to infective soil stages because these nematodes respond to host cues. The distance migrated may be a function of some nematodes waiting passively for a host while others are dispersers.Like other organisms, nematodes have strategies to resist adverse environmental conditions. Such strategies may have behavioural, biochemical or morphological components but all three have strong associations with each other. In Chapter 13 (Survival Strategies'), David Wharton describes various behavioural approaches nematodes employ to avoid or mitigate stress, including synchronizing parasite life cycles with host availability or migration (e.g. phoresy) to escape environmental extremes until favourable conditions return. Other species develop a degree of tolerance or resistance. These adaptive strategies enhance survival under biological (food inadequacy, predation, pathogens and competition), physical (temperature, desiccation, pressure and radiation) or chemical (pH, osmotic stress, anoxia) stress. Wharton explains how various tactics and mechanisms govern nematode behaviour in challenging environments. The reasons for and mechanisms of attaining resting, infective and dauer stages, diapause and egg diapause, arrested development and delays in the life cycles are elaborated in this chapter.
Microbial Challenge by Robert I. Krasner (ASM)
undergraduate text on human-microbe interactions. Provides an understanding of
the biology of the microbial world and its effects on daily life. Contains three
sections titled, challenges, meeting the challenges, and current challenges.
Topics include microbial diseases, biological warfare, and antibiotic
resistance. Full-color format.
Accessible and fascinating
The Microbial Challenge is on human‑microbe interactions, intended as a text
for use in undergraduate science courses. Designed to help students better
understand the biology of the microbial world and its effect on their lives,
this timely volume covers issues of vital importance, including biological
warfare and terrorism, antibiotic resistance, the global impact of microbial
diseases, and immunization.
A hybrid of microbiology and public health,
The Microbial Challenge emphasizes the significance of microbes in everyday
living. Students are led to understand public health problems and are provided a
greater awareness of disease on a global scale through an examination of
microbial (infectious) diseases and their societal consequences, including
descriptions of some of the major microbial diseases through the ages, efforts
to meet the challenges raised by microbes, and public health measures of
protection and surveillance put in place to keep ever‑challenging microbes at
bay. The beneficial nature of microbes is also examined; they are vital to the
cycles of nature, play an important role in the food industry, and are
significant tools in biological research.
Richly illustrated with many photos from the author's
extensive personal collection taken during his numerous trips abroad,
The Microbial Challenge is ideal for students not majoring in science, for
allied health sciences courses, and for public health courses. It can also be
used as supplementary reading in standard microbiology and other biology
A Chronology of Microbiology in Historical Context by Raymond W. Beck (AMS) This informative and absorbing chronology presents events in the annals of microbiology in light of their historical context and identifies those individuals who made these events happen. Beginning in the 3rd millennium B.C. with citations of ancient medicine and diseases, the chronology follows the development of microbiology and related sciences through the 18th and 19th centuries and culminates with the explosion of discoveries in the late 20th century.
Environmental Microbiology by Alan H. Varnum, photography by Malcolm G. Evans (ASM) A reference for students and professionals in microbiology, microbial science, and environmental science, combining basics of science with recent advances, plus high-quality color photos. Interactions between the environment and the dominant microflora are discussed, as are interactions between the various components of microflora; however, emphasis is on understanding principles. After an overview of environmental microbiology, sections cover aquatic, terrestrial, and extreme environments, with chapters on areas such as marine and freshwater environments, micro-organisms and higher plants, and saline environments. Varnam is affiliated with the University of North London, UKMolecular Mimicry, Microbes, and Autoimmunity edited by Madeleine W. Cunningham, Robert S. Fujinami (ASM) focuses on studies that identify mimicry between infectious agents and host molecules. The 18 papers examine the origins of the field, the current status, and the new developments that could lead to a better understanding of molecular mimicry and how infectious agents trick the host immune system to turn against a particular organ or group of organs in the human body. Topics include heart disease, Lyme arthritis, diabetes, Chagas' disease, peptide mimicry of streptococcal group A carbohydrate, peptide induction of systemic lupus autoimmunity, and the role of T cells in mimicry and determinant spreading.
Dictionary of Microbiology and Molecular Biology by Paul Singleton, Diana Sainsbury, 3rd edition (Wiley) covers pure and applied microbiology, from taxonomy of algae, bacteria, fungi, protozoa and viruses to microbiology associated with medicine, the food industry, plant pathology and veterinary science. Microbiologically relevant aspects of molecular biology are also included. Entries range from concise definitions to mini-reviews, many of one page or more in length. This Third Edition has been extensively updated with 4,000 expanded and new entries and contains a total of 18,000 entries all-together.
Unlike similar titles in this field Dictionary of Microbiology and Molecular Biology supplies references to extend the range and usefulness of the dictionary. * A complex system of internal cross-referencing links entries of related interest and allows topics to be seen in a broader, interdisciplinary context. * Extensively updated with 4,000 expanded and new entries
Editor’s summary: In writing this new edition of the Dictionary we had several aims in mind. One of these was to provide clear and up‑to‑date definitions of the numerous terms and phrases which form the currency of communication in modern microbiology and molecular biology. In recent years the rapid advances in these disciplines have thrown up a plethora of new terms and designations which, although widely used in the literature, are seldom defined outside the book or paper in which they first appeared; moreover, ongoing advances in knowledge have frequently demanded changes in the definitions of older terms ‑ a fact which is not always appreciated and which can therefore lead to misunderstanding. Accordingly, we have endeavoured to define all of these terms in a way which reflects their actual usage in current journals and texts, and have also given (where appropriate) former meanings, alternative meanings, and synonyms.
A second ‑ but no less important ‑ aim was to encapsulate and integrate, in a single volume, a body of knowledge covering the many and varied aspects of microbiology. Such a reference work would seem to
be particularly useful in these days of increasing specialization in which the reader of a paper or review is often expected to have prior knowledge of both the terminology and the overall biological context of a given topic. It was with this in mind that we aimed to assemble a detailed, comprehensive and interlinked body of information ranging from the classical descriptive aspects of microbiology to current developments in related areas of bioenergetics, biochemistry and molecular biology. By using extensive cross‑referencing we have been able to indicate many of the natural links which exist between different aspects of a particular topic, and between the diverse parts of the whole subject area of microbiology and molecular biology; hence the reader can extend his knowledge of a given topic in any of various directions by following up relevant cross‑references, and in the same way he can come to see the topic in its broader contexts. The dictionary format is ideal for this purpose, offering a flexible, `modular' approach to building up knowledge and updating specific areas of interest.
There are other more obvious advantages in a reference work with such a wide coverage. Microbiological data are currently disseminated among numerous books and journals, so that it can be difficult for a reader
to know where to turn for information on a term or topic which is completely unfamiliar to him. As a simple example, the name of an unfamiliar genus, if mentioned out of context, might refer to a bacterium, a fungus, an alga or a protozoon, and many books on each of these groups of organisms may have to be consulted merely to establish its identity; the problem can be even more acute if the meaning of an unfamiliar term is required. A reader may therefore be saved many hours of frustrating literature‑searching by a single volume to which he can turn for information on any aspect of microbiology.An important new feature of this edition is the inclusion of a large number of references to recent papers, reviews and monographs in microbiology and allied subjects. Some of these references fulfil the conventional role of indicating sources of information, but many of them are intended to permit access to more detailed information on particular or general aspects of a topic ‑ often in mainstream journals, but sometimes in publications to which the average microbiologist may seldom refer. Furthermore, most of the references cited are themselves good sources of references through which the reader can establish the background of, and follow developments in, a given area.
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