Many marine bacteria have evolved to grow optimally at either high (copiotrophic) or low (oligotrophic) nutrient concentrations, enabling different species to colonize distinct trophic habitats in the oceans. Here, we compare the genome sequences of two bacteria, Photobacterium angustum S14 and Sphingopyxis alaskensis RB2256, that serve as useful model organisms for copiotrophic and oligotrophic modes of life and specifically relate the genomic features to trophic strategy for these organisms and define their molecular mechanisms of adaptation. We developed a model for predicting trophic lifestyle from genome sequence data and tested >400,000 proteins representing >500 million nucleotides of sequence data from 126 genome sequences with metagenome data of whole environmental samples. When applied to available oceanic metagenome data (e.g., the Global Ocean Survey data) the model demonstrated that oligotrophs, and not the more readily isolatable copiotrophs, dominate the ocean's free-living microbial populations. Using our model, it is now possible to define the types of bacteria that specific ocean niches are capable of sustaining.microbial adaptation and ecology ͉ microbial genomics and metagenomics ͉ monitoring environmental health ͉ trophic adaptation T he marine environment is the largest habitat on Earth, accounting for Ͼ90% of the biosphere by volume and harboring microorganisms responsible for Ϸ50% of total global primary production. Within this environment, marine bacteria (and archaea) play a pivotal role in biogeochemical cycles while constantly assimilating, storing, transforming, exporting, and remineralizing the largest pool of organic carbon on the planet (1).Nutrient levels in pelagic waters are not uniform. Large expanses of water are relatively nutrient depleted (e.g., oligotrophic open ocean water), whereas other zones are relatively nutrient rich (e.g., copiotrophic coastal and estuarine waters). Local variations in nutrient content can occur because of physical processes, including upwelling of nutrient rich deep waters or aeolian and riverine deposition, or biological processes such as phytoplankton blooms or aggregation of particulate organic matter. In addition, heterogeneity in ocean waters is not limited to gross differences in nutrient concentrations, but extends to microscale patchiness that occurs throughout the continuum of ocean nutrient concentrations (2).In ecological terms, bacteria are generally defined as rstrategists, having a small body, short generation time, and highly dispersible offspring. Although this strategy is broadly true compared with macroorganisms, bacteria have evolved a wide range of growth and survival strategies to maximize reproductive success. In particular, nutrient type and availability have provided strong selective pressure for defining lifestyle strategies among marine bacteria. However, although a large number of copiotrophic marine organisms (and fewer oligotrophs) have been cultured, the study of trophic strategy has been impaired by a lack of unders...

In most environments, bacteria reside primarily in biofilms, which are social consortia of cells that are embedded in an extracellular matrix and undergo developmental programmes resulting in a predictable biofilm 'life cycle'. Recent research on many different bacterial species has now shown that the final stage in this life cycle includes the production and release of differentiated dispersal cells. The formation of these cells and their eventual dispersal is initiated through diverse and remarkably sophisticated mechanisms, suggesting that there are strong evolutionary pressures for dispersal from an otherwise largely sessile biofilm. The evolutionary aspect of biofilm dispersal is now being explored through the integration of molecular microbiology with eukaryotic ecological and evolutionary theory, which provides a broad conceptual framework for the diversity of specific mechanisms underlying biofilm dispersal. Here, we review recent progress in this emerging field and suggest that the merging of detailed molecular mechanisms with ecological theory will significantly advance our understanding of biofilm biology and ecology.

Mature Pseudomonas aeruginosa biofilms undergo specific developmental events. Using a bacteriophage mutant, generated by deletion of the entire filamentous Pf4 prophage, we show that the phage is essential for several stages of the biofilm life cycle and that it significantly contributes to the virulence of P. aeruginosa in vivo. Here, we show for the first time that biofilms of the Pf4 phage-deficient mutant did not develop hollow centres or undergo cell death, typical of the differentiation process of wild-type (WT) P. aeruginosa PAO1 biofilms. Furthermore, microcolonies of the Pf4 mutant were significantly smaller in size and less stable compared with the WT biofilm. Small colony variants (SCVs) were detectable in the dispersal population of the WT biofilm at the time of dispersal and cell death, whereas no SCVs were detected in the effluent of the Pf4 mutant biofilm. This study shows that at the time when cell death occurs in biofilms of the WT, the Pf4 phage converts into a superinfective form, which correlates with the appearance of variants in the dispersal population. Unexpectedly, mice infected with the Pf4 mutant survived significantly longer than those infected with its isogenic WT strain, showing that Pf4 contributes to the virulence of P. aeruginosa. Hence, a filamentous prophage is a major contributor to the life cycle and adaptive behaviour of P. aeruginosa and offers an explanation for the prevalence of phage in this organism.

Persistence of the opportunistic bacterial pathogen Vibrio cholerae in aquatic environments is the principal cause for seasonal occurrence of cholera epidemics. This causality has been explained by postulating that V. cholerae forms biofilms in association with animate and inanimate surfaces. Alternatively, it has been proposed that bacterial pathogens are an integral part of the natural microbial food web and thus their survival is constrained by protozoan predation. Here, we report that both explanations are interrelated. Our data show that biofilms are the protective agent enabling V. cholerae to survive protozoan grazing while their planktonic counterparts are eliminated. Grazing on planktonic V. cholerae was found to select for the biofilm-enhancing rugose phase variant, which is adapted to the surface-associated niche by the production of exopolymers. Interestingly, grazing resistance in V. cholerae biofilms was not attained by exopolymer production alone but was accomplished by the secretion of an antiprotozoal factor that inhibits protozoan feeding activity. We identified that the cell density-dependent regulator hapR controls the production of this factor in biofilms. The inhibitory effect of V. cholerae biofilms was found to be widespread among toxigenic and nontoxigenic isolates. Our results provide a mechanistic explanation for the adaptive advantage of surface-associated growth in the environmental persistence of V. cholerae and suggest an important contribution of protozoan predation in the selective enrichment of biofilm-forming strains in the out-of-host environment.grazing ͉ resistance ͉ protozoa ͉ quorum sensing E pidemics of cholera, an acute intestinal infection caused by toxigenic strains of the facultative pathogen Vibrio cholerae, are a major public health problem in developing countries around the globe. Both toxigenic and nontoxigenic strains of V. cholerae are natural inhabitants of a wide range of aquatic ecosystems, including estuarine and coastal waters, that provide the environmental reservoir of virulent V. cholerae strains (1). The fact that many environmental nontoxigenic strains carry virulence genes (2, 3) and that the occurrence of epidemics coincides with the increased prevalence of the causative V. cholerae strain in the aquatic environment (4, 5) supports the notion of an environmental origin of toxigenic V. cholerae clones. This view has led to the hypothesis that cholera epidemics are triggered by environmental factors and selective forces governing aquatic microbial communities. In recent years, studies on the ecology of V. cholerae have considerably increased our understanding of physical and biological parameters that influence the persistence of V. cholerae in the environment and hold the potential to predict the outbreak of cholera epidemics (6).As a member of the natural bacterioplankton community, V. cholerae is an integral part of the pelagic microbial food web and is thus constrained in its growth and survival by the predatory action of bacterivorous protists, so...