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The Department of Plant Pathology and Microbiology
Robert H. Smith Faculty of Agriculture, Food and Environment
The Hebrew University of Jerusalem
Predatory bacteria
Predation is an important ecological force for all life forms, including prokaryotes. Bacteria that prey upon other bacteria are ubiquitous in the environment. They exhibit a variety of hunting strategies, belong to many taxa and widely differ in morphological, physiological and molecular features. Among these predators, Bdellovibrio and like organisms (BALOs) are obligate predatory bacteria of gram negative cells. Their life cycle is fascinating: small, highly motile cells attach to and usually penetrate prey cells. They then engage in growth and replication at the expense of the prey's contents, yielding progeny cells that lyze the remains of the consumed host cell.
Ecology and evolution of bacterial predators
Bdellovibrio and like organisms (BALOs) are found in many habitats. Over the years, they have been isolated from and detected in soil, in the rhizosphere, in fresh, brackish and marine water, in wastewater and in extreme environments. BALOs have also been found in the guts of various animals.
The lab's research in BALO ecology has been centered on the study of BALO diversity and phylogeny. We isolated numerous BALO strains that were analyzed with molecular and phenotypic markers. The culture-independent tools we have developed allow direct assessment of BALO diversity without relying on previous isolation. Phylogenetic reconstructions allow us to formulate new hypotheses on the evolution of bacterial predation and on its past and present role in nature.
The life cycle of Bdellovibrio bacteriovorus
B. bacteriovorus' cell cycle is dimorphic. During attack phase, small, free-living and highly motile cell possessing a long sheathed flagellum search for adequate gram negative prey cells. Encounter between a predator and a prey may lead to irreversible attachement and penetration of the predator into the prey' periplasm, forming a bdelloplast. This event triggers growth of the invading cell and rounds of replication of its genetic material.. This stage ends when the prey' s cytoplasm has been consumed. The long, polynucleoid cell divides into progeny attack phase cells that lyze the prey remains to start anew. Host-independent mutant strains able to grow in a rich medium without prey can be isolated. These organisms retain the dimorphic phenotype of wild type strains.
We are using proteomic and gene expression approaches to analyze B. bacteriovorus' cell cycle and the bacterium's predatory arsenal. Proteins are isolated and analyzed by mass spectrometry to determine the fluctuations of the expressed proteome in relation to growth stages. The temporal and spatial expression of selected proteins as well as their functions are further characterized by gene expression analysis and biochemical tests.
