Prokaryotic Nitrogen Fixation: A Model System for the Analysis of a Biological Process Book Reviews
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Review by July 2000 In Prokaryotic Nitrogen Fixation: A Model System for the Analysis of a Biological Process, an attempt has been made to present a state-of-the-art summary of the different aspects of research in the area of biological nitrogen fixation. The organization of the book is straight forward. In the first chapters, the
nitrogen cycle is explained and oceanic nitrogen fixation is discussed based on
the filamentous non-heterocystous cyanobacterium
Trichodesmium. In the following six chapters, diverse studies on structure and function of the nitrogenase enzyme are summarized, ranging from site-directed mutagenesis of bacterial genes encoding components of the nitrogenase complex, to structural analysis of nitrogenase protein components by crystallography to infra-red
spectroscopy of functioning nitrogenase. In the next section, some examples from
free-living nitrogen-fixing bacteria are used to illustrate the possibilities for the
regulation of nitrogen fixation, and aspects of the evolution of symbiotic nitrogen
fixation are discussed in three excellent chapters on the evolution of root
nodule symbioses and one on termite symbionts. The 20 following chapters are
devoted to symbiotic nitrogen fixation in legume root nodules, without a
doubt the most well researched symbiotic nitrogen-fixing system. Rhizobial
chemotaxis and competition, the signal exchange between both symbionts and the
infection process in general, as well as the role of rhizobial surface structures in
symbiosis are discussed. Eight chapters cover plant gene expression in the course
of nodule organogenesis and nodule metabolism. Progress made in genomics
of diazotrophic bacteria is discussed based on three rhizobial and one
archaeal example. One of the rhizobial examples covers the famous symbiosis island'
in Mesorhizobium, which is transposable and can render a non-symbiotic strain of Mesorhizobium fully symbiotic. The last five chapters deal with associations of diazotrophic bacteria with grasses, including the tricky subject of quantifying the contribution of plant-associated biological nitrogen fixation and the agronomical output of such associations.
The individual chapters are well written by expert authors and can be
recommended to anyone interested in these specific areas of the field.
... the book presents a nicely constructed, state-of-the-art overview of
rhizobia-legume symbioses and provides information about several other
nitrogen-fixing systems as well as information about basic aspects of nitrogen fixation such
as nitrogenase structure and regulation. Many chapters contain schematic
representations of developmental pathways, metabolic cycles and signal
transduction schemes, which might be useful for a lecturer. Technical questions - such as
the specimen preparation for microscopical analysis of the rhizobial infection
process, or the design of oligonucleotide probes for identification of
diazotrophic endophytes of grasses - are addressed and discussed critically in several
chapters.
Altogether, the book represents an excellent introduction to the field
of symbioses between plants and nitrogen-fixing bacteria, and a splendid
update about research on rhizobia-legume symbioses, and should be found on
the shelves of microbiology and plant biology libraries.
Review by Applied Soil Ecology 16: 193-194. 2001 I purchased a copy of this book at its pre-publication price of £104, but decided to accept a review copy as well because the volume covers a range of topics of interest to several colleagues. This review draws on their comments, but I accept responsibility for the final copy. Dr. Triplett has assembled an impressive list of experts and persuaded them to produce manuscripts quickly, so that the material in this volume is generally very up-to-date. It has a
comprehensive coverage of all prokaryotic nitrogen fixing organisms, the only current volume to my knowledge to do this. The work is divided into seven sections, beginning with one on the nitrogen cycle. The
first of the two papers in this section gives a brief overview of the nitrogen cycle and is useful for putting nitrogen fixation into context. The second chapter is solely on the marine organism
Trichodesmium. This is a very interesting summary of nitrogen fixation in the oceans, but I was sorry that there were not other chapters on the global significance of biological nitrogen fixation, however difficult this may be to assess. Readers may care to know of a paper in press (Vitousek et al., 2000) attempting to do this. Section 2 consists of six chapters and covers the structure and function of nitrogenase. It is an excellent source of readable material, especially for those of us that are not specialists in this field.
The three chapters in the next section covers regulation of nitrogen fixation at the genetic and molecular level. This is appropriate for a book with an emphasis on the prokaryotes, but persons
interested in symbiotic systems may be disappointed in the coverage.
The reason that I purchased a pre-publication copy of this book was the flyer which extolled the coverage of evolution. I have to say that I was disappointed in this section. The four chapters are
well written, but do not come to grips with some of the more interesting aspects, particularly of co-evolution in symbiotic systems. Only Benson and Clawson (actinorhizal plants) put a geological
time scale in their chapter. The inclusion of a chapter on termite symbionts, though very interesting in itself, was more ecological than evolutionary.
The largest section, the fifth, has 20 chapters on legumes and is divided into three sections, covering infection, nodule development and metabolism, and model legumes systems respectively.
Much, but not all, of the material is covered in more depth in the volume edited by Spaink et al. (1998). However the chapters in the present book (not only in this section) are characterised by a very
good coverage of the literature and there are some excellent photographic and other illustrations.
Genomics are the topic of the four chapters in Section 6. I found the account of methanogens by Leigh of particular interest as it summarised the current state of knowledge on these Archaea.
The chapter could have been equally at home in the evolution section.
The final section has five chapters on bacterial-grass associations, a topic which has been very controversial for many years. As with much of this volume, most of the data summarised have
been published elsewhere. However, Boddey et al., in their consideration of how to assess nitrogen fixation in grasses have suggested a new way (using ELISA techniques) to count the number of
bacteria present. This essential piece of information has been badly neglected in attempts to quantify nitrogen fixation in grasses and similar systems. The paper of Sevilla and Kennedy gives useful
15N2 data for sugar cane plantlets, although I am not fully persuaded that this represents a 'new type of symbiosis'.
Whilst I fully sympathise with the emphasis on legumes, I think the cyanobacteria might have had more coverage, especially the symbiotic systems which are scarcely mentioned. Fortunately
these have been the subject of a recent review (Rai et al., 2000).
The main positive features of this book are the up-to-date literature coverage and (with the exception of cyanobacterial symbioses and to a lesser extent actinorhizal systems) the wide coverage
of prokaryotes. The book is well edited and there are few errors. Unfortunately, these advantages are offset by the very high price of the volume.
References
Rai, A.N., Södebäck, E., Bergman, B., 2000. Cyanobacterium- plant symbioses. New Phytologist. 147, 449-48l.
Spaink, H.P., Kondorosi, A., Hooykaas, P.J.J. (Eds.), 1998. The
Rhizobiaceae. Kiuwer Academic Publishers, Dordrecht. Vitousek, P.M., Cassman, K., Cleveland, C., Crews, T., Field, C.B., Grimm, N.B., Howarth, R.W., Marino, R., Martinelli, L., Rastetter, E.B., Sprent, J.I., 2000. Towards an ecological understanding of biological nitrogen fixation. Biogeochem., in press.
Microbiology Today 28: 156. August 2001 This book is poles apart from the excellent, concise student-orientated Nitrogen Fixation (3rd edition) by John Postgate (Cambridge). At 800 pages, and this price, it is aimed squarely at the nitrogen fixation specialist who requires up-to-date information across this bewilderingly broad field. The chapters span a gamut ot biological disciplines, from protein crystallography to mellifluous model legumes, via evolution, gene regulation and biochemistry. The contents show how an apparently simple biological process - the formation of ammonia from dinitrogen - remains a focus of attention for those interested in, for example metallobiochemistry, genomics and environmental microbiology. The book is well produced and illustrated and can be recommended, although I felt that a more detailed index would serve the contents better. J. Plant Nutr. Soil Sci. 164: 463. August 2001 Roughly 180 Tg N /yr enter terrestrial ecosystems by prokaryotic N2- fixation, about 55% of the total N input. For this reason, N2-fixation is still a major subject of soil biology with 1130 contributions according to the CAB abstracts within the last 10 years after a history of more than 100 years of research. In comparison, 2300 contributions were abstracted by the CAB on microbial biomass during the same period. The comprehensive volume edited by Eric Triplett consists of 44 chapters, written by 81 authors including Anton Hartmann and Michael Schloter, DBG-members from the Institute of Soil Ecology, GSF-Oberscbleillheim near Munich. The main processes of the nitrogen cycle are explained in the first chapter, and the biology of oceanic nitrogen fixation is demonstrated in the next chapter using the filamentous non-heterocystous cyanobacterium Trichodesmium. In chapters 3 to 8, studies on the structure, functioning, and biosynthesis of several nitrogenase components are reviewed, considering analytical tools such as x-ray crystallography or stopped-flow Fourier transform infrared spectroscopy (SF-FTIR). This section is followed by 3 chapters illustrating the possibilities for the regulation of N2-fixation in free-living bacteria. Chapters 12 to 15 portray aspects of the evolution of symbiotic N2-fixation in legumes, angiosperms, and termites. The following 20 chapters exclusively deal with the biology of symbiotic N2- fixation in legumes, the most well investigated process in soil biology. This section starts with 9 chapters on the infection process, followed by 8 chapters referring to nodule development and metabolism and ends with 3 chapters looking at model systems for the analysis of N2-fixing symbiosis. Progress made in genomics of diazotrophic microorganisms is shown using one methanogenic archaeal and three rhizobial examples in chapters 36-39. The last 5 chapters focus on associations of N2-fixing bacteria with grass species, especially maize and sugarcane, acknowledging the recent pioneer work of the late Johanna Dobereiner. The individual chapters are well written by expert authors and can be recommended to anyone interested in these specific areas of the field. Many chapters contain schematic representations of developmental pathways, metabolic cycles and signal transduction schemes, which might be useful for lecturers. Technical questions, such as specimen preparation for microscopical analysis of the rhizobial infection process, or the design of oligonucleotide probes for identification of N2-fixing endophytes are critically discussed in the respective chapter. Not much is known about the agronomical output of such associations. As yet, data in support of plant growth benefits to maize accrued via nitrogenase activity are lacking, and this book does not contribute anything to this subject or to any other ecological aspects of N2-fixation. The key problem of this process is energy supply to the prokaryotic microorganisms. The energy demand for fixing 1 mol N2 as 2 NH4 is 675 kJ, neglecting the further energy demand of microorganisms for growth, nodule formation, and maintenance. This energy demand must significantly reduce the yield of field crops, which is especially a problem if large starch and cellulose containing parts of the plant, if not the whole plants, are harvested instead of the small protein-rich seeds of legumes. Legumes have minor importance as crops in conventional farming systems, where mineral N fertilizers are cheap. In ecological farming systems, where legume are an important part of crop rotations, the motivation to use genetically engineered or manipulated associations of plant and diazotrophic microorganisms is very low. There is no doubt that this comprehensive volume will serve as a valuable reference work for all biologists working in this field, and it will also be of interest to researchers studying metal-containing enzymes, symbiosis, genome research, environmental microbiology, plant metabolism, infection events, and prokaryote-eukaryote interaction. However, the book is not very useful for persons interested in the ecological and environmental aspects of N2-fixation and its consequence for plant nutrition, i.e. for most of us soil scientists. It is amazing to realize the discrepancy between the sophisticated and very advanced research and the practical consequences for land use and crop production.
Katharina Pawlowski
Albrecht von Haller Institute for Plant Sciences, University of Göttingen, Untere KarspüIe 2, Plant Biochemistry, 37073 Göttingen, Germany (e-mail: kpawlow©gwdg.de)
J. Sprent Department of Biological Sciences University of Dundee, Dundee, Scotland DDJ 4HN, UK (email: j.i.sprent@dundee.ac.uk)
Review by
Robert Poole
University of Sheffield
Review by
Rainer Georg Joergensen
Witzenhausen, Germany