Bacterial pathogenesis of plants and animals

BOOK

REVIEWS

particularly in the chapters on specimen handling and processing, microscopy and microbial classification, and identification. Photographs are used in some chapters, many in high-quality full colour where extra detail is essential to help the reader; growth stages in Plasmodium vivax, amoeba cysts

At the

cusp

Bacterial

Pathogenesis of Plants and Animals edited by Jeffery L. Dangl

Springer-Verlag, 1994.L89.30 hbk (x+ 343 pages)ISBN 3 540573917

A

s

I was watering my plants in the greenhouse I had a bad cough; this reminded me of the very interesting book on animal and plant pests I was reviewing. In the past decade, the application of the concepts and methodologies of bacterial genetics and molecular biology to the study of animal and plant pathogens has led to significant advances in our understanding of the mechanisms governing pathogenicity. These studies have revealed common themes in plant and animal pathology, including the existence of global regulatory networks controlling sets of pathogenicity genes and the secretion of ‘virulence’ proteins. Bacterial Pathogenesis of Plants and Animals contains seven chapters on plant-bacteria interactions, followed by seven chapters on animal pathogens. These chapters, written by leading scientists in these fields, are very clear and comprehensive reviews of molecular and cellular aspects of the pathogenesis of selected animal and plant pathogens. They provide insight into the molecular strategies and mechanisms that bacteria use to enter their victims, defeat defense mechanisms, colonize and survive in their hosts. The inspiration for this combination of papers was the finding that several plant- and animal-pathogenic bacteria use a common and specific pathway to secrete proteins involved in the interaction with their respective hosts. This secretion machinery, called the type III secretion pathway’, was initially recognized in Yersinia, where it is as-

TRENDS

and helminth parasites in tissues are good examples. The fundamental philosophy of the manual is that it is intended to guide clinical microbiologists in the selection, performance and interpretation of laboratory procedures for diagnostic and therapeutic applications - it certainly succeeds,

sociated with the secretion of Yops. The functions of several Yops have been determined and their role in pathogenesis clearly established. The secretion of Yops requires at least 19 genes, many of which have counterparts in Shigella flexneri and Salmonella typhimurium, where they control the secretion of proteins involved in the invasion of eukaryotic cells. Plant-pathogenic bacteria (such as Erwinia amylovora, Erwinia chrysantbemi, Pseudomonas solanacearum, Pseudomonas syringae and Xanthomonas campestris) have a homologous secretion machinery encoded by the hrp genes. The Hrp pathways in E. amylovora and P. syringae pv. syringae (harpins) and P. solanacearum (PopA) have been shown to control the secretion of proteins that induce necrotic lesions after infiltration into plant leaves. Pseudomonas syringae pv. syringae and P. solanacearum may secrete other proteins via the Hrp pathway, but these have not yet been characterized. A key question for plant pathologists concerns the relationship between hrp genes and the ‘enigmatic aviruthe lence genes’, which control race-cultivar specificity of plant pathogens. Are the products of some of these genes secreted via the Hrp machinery? The animaland plant-pathogenic bacteria presented in this book secrete other sets of virulence proteins that transit via type I, type II or specific secretion pathwaysi. These include the toxins, adhesins or invasins produced by pathogenic Salmonella, Listeria, Shigella, Yersinia, Vibrio, Neisseria or Bordetella and the battery of extracellular enzymes that can degrade plant tissues produced by X. campestris or the soft-rot erwinias. If extracellular proteins seem to be ‘primary weapons in the parasitic

INMICROBIOLOGY

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and it is also an important reference source for infectious-disease specialists, medical technologists, students and their teachers. David R. Morgan Scientific Affairs Dept, British Medical Association, Tavistock Square, London, UK WClH 9JP

attack of most bacteria on eukaryotic hosts’, some bacteria have developed other strategies. For example, Agrobacterium tumefaciens transfers a piece of DNA (the T-DNA) into the plant cell where it is integrated into the nuclear genome. Another good example is the symbiosis between rhizobia and legumes. Rbizobium produces substituted lipo-oligosaccharides (the Nod factors) that induce the formation of a new organ (the nodule) on the roots of host plants. Is Rbizobium a highly sophisticated pathogen that avoids host defense mechanisms? In most cases, the production of sets of virulence factors has been shown to be regulated by ‘global regulatory networks’. This coordination of gene expression certainly reflects the contribution of different synergizing factors during specific stages of the infectious process. Finally, the emergence of common themes in animal and plant pathology, highlighted in this book, is well illustrated by the recently published work of Rahme et al.z on Pseudomonas aeruginosa, which shows that three bacterial genes encode virulence factors that are required for the full expression of pathogenicity in both plants and animals. In summary, this very interesting book is a significant contribution to the field of bacterial pathogenesis. I now leave you to water my plants. Matthieu Arlat Laboratoire de Biologie Moleculaire des Relations Plantes-Microorganismes, INRA-CNRS, BP 27,3 1326 Castanet-tolosan, France References 1 Salmond, G.P.C. and Reeves,P.J. (1993) Trends Biochem.Sci.l&7-12 2 Rahme, L.G. et al. (1995) Science268, 1899-1902