Phytoplankton blooms characterize temperate ocean margin zones in spring. We investigated the bacterioplankton response to a diatom bloom in the North Sea and observed a dynamic succession of populations at genus-level resolution. Taxonomically distinct expressions of carbohydrate-active enzymes (transporters; in particular, TonB-dependent transporters) and phosphate acquisition strategies were found, indicating that distinct populations of Bacteroidetes, Gammaproteobacteria, and Alphaproteobacteria are specialized for successive decomposition of algal-derived organic matter. Our results suggest that algal substrate availability provided a series of ecological niches in which specialized populations could bloom. This reveals how planktonic species, despite their seemingly homogeneous habitat, can evade extinction by direct competition.

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In Escherichia coli, starvation (stationary-phase)-mediated differentiation involves 50 or more genes and is triggered by an increase in cellular s levels. Western immunoblot analysis showed that in mutants lacking the protease ClpP or its cognate ATPase-containing subunit ClpX, s levels of exponential-phase cells increased to those of stationary-phase wild-type cells. Lack of other potential partners of ClpP, i.e., ClpA or ClpB, or of Lon protease had no effect. In ClpXP-proficient cells, the stability of s increased markedly in stationary-phase compared with exponential-phase cells, but in ClpP-deficient cells, s became virtually completely stable in both phases. There was no decrease in ClpXP levels in stationary-phase wild-type cells. Thus, s probably becomes more resistant to this protease in stationary phase. The reported s -stabilizing effect of the hns mutation also was not due to decreased protease levels. Studies with translational fusions containing different lengths of s coding region suggest that amino acid residues 173 to 188 of this sigma factor may directly or indirectly serve as at least part of the target for ClpXP protease.Starvation is a common experience for bacteria in nature (26), and in certain bacteria this stress triggers an elaborate differentiation response, culminating in the formation of spores that are highly resistant, morphologically distinct structures (3,12,16). In most other bacteria, this differentiation is more subtle and is not accompanied by a comparable morphological change. Yet 50 or more genes, constituting several temporal classes, have been implicated in starvation-induced development of a resistant cellular state in Escherichia coli (19,25). E. coli has been most intensively studied in this respect, but as similar findings have been made in marine vibrios (18), Salmonella typhimurium (32), and Pseudomonas putida (8, 17), development of a generalized resistant state is probably a universal response of bacteria to starvation.In E. coli, an increase in the concentration of a secondary sigma factor, s (product of the rpoS gene), in stationary (starvation) phase appears to be a major trigger for such differentiation. This increase involves regulation at the transcriptional, translational, and post-translational levels (20,23,28,39). With respect to the last-mentioned mechanism, it was recently shown that the stability of s increased markedly in stationary phase (20). In this study, we have investigated the basis of this altered stability. We report that s becomes more stable in exponential phase in the absence of the ClpXP protease from the cells but not that of ClpAP, ClpB, or Lon protease; that the increased resistance of s in stationary phase is not due to a decreased concentration of the ClpXP protease in this phase;and that a stretch of amino acids near the middle of s appears to be required for its sensitivity to ClpXP activity.(A report of these findings was presented previously [21].) MATERIALS AND METHODSBacterial strains and construction of lacZ translational fu...

Low nutrient and energy availability has led to the evolution of numerous strategies for overcoming these limitations, of which symbiotic associations represent a key mechanism. Particularly striking are the associations between chemosynthetic bacteria and marine animals that thrive in nutrient-poor environments such as the deep sea because the symbionts allow their hosts to grow on inorganic energy and carbon sources such as sulfide and CO 2 . Remarkably little is known about the physiological strategies that enable chemosynthetic symbioses to colonize oligotrophic environments. In this study, we used metaproteomics and metabolomics to investigate the intricate network of metabolic interactions in the chemosynthetic association between Olavius algarvensis, a gutless marine worm, and its bacterial symbionts. We propose previously undescribed pathways for coping with energy and nutrient limitation, some of which may be widespread in both freeliving and symbiotic bacteria. These pathways include (i) a pathway for symbiont assimilation of the host waste products acetate, propionate, succinate and malate; (ii) the potential use of carbon monoxide as an energy source, a substrate previously not known to play a role in marine invertebrate symbioses; (iii) the potential use of hydrogen as an energy source; (iv) the strong expression of high-affinity uptake transporters; and (v) as yet undescribed energy-efficient steps in CO 2 fixation and sulfate reduction. The high expression of proteins involved in pathways for energy and carbon uptake and conservation in the O. algarvensis symbiosis indicates that the oligotrophic nature of its environment exerted a strong selective pressure in shaping these associations.3-hydroxypropionate bi-cycle | Calvin cycle | proton-translocating pyrophosphatase | pyrophosphate dependent phosphofructokinase | metagenomics G rowth in nutrient-limited environments presents numerous challenges to organisms. Symbiotic and syntrophic relationships have evolved as particularly successful strategies for coping with these challenges. Such nutritional symbioses are widespread in nature and, for example, have enabled plants to colonize nitrogen-poor soils and animals to thrive on food sources that lack essential amino acids and vitamins (1). Chemosynthetic symbioses, discovered only 35 years ago at hydrothermal vents in the deep sea, revolutionized our understanding of nutritional associations, because these symbioses enable animals to live on inorganic energy and carbon sources such as sulfide and CO 2 (2, 3). The chemosynthetic symbionts use the energy obtained from oxidizing reduced inorganic compounds such as sulfide to fix CO 2 , ultimately providing their hosts with organic carbon compounds. Chemosynthetic symbioses thus are able to thrive in habitats where organic carbon sources are rare, such as the deep sea, and the symbionts often are so efficient at providing nutrition that many hosts have reduced their digestive systems (4).The marine oligochaete Olavius algarvensis is a particularly extre...