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Chapter 16 : Life in Extremely Dilute Environments: the Major Role of Oligobacteria
Oligobacteria are bacteria adapted to growth in organic nutrient conditions of the marine and other aquatic environments. Their main food source is dissolved photosynthetically produced organic material. The major products are carbon dioxide, minerals, and cellular biochemicals. Oligobacteria evolved to sustain at nutrient concentrations that are small. The properties of oligobacteria are based largely on copeotrophs such as Escherichia coli because oligobacteria have been unavailable in sufficient mass for investigation. Phytoplankton collect nutrients and reduce them to concentrations that are small as well. Some, such as Synechococcus and Prochlorococcus, are very small giving a large surface- to-volume ratio for mineral collection. This ability is smaller than for oligobacteria because phytoplankton must synthesize their own organics as well. The problem of oligobacterial growth in natural water systems is one of nutrient acquisition. Rates measured are generally near upper limits for oligobacteria because the focus is often on photic zone processes in active regions. However, the cosmopolitan distribution of oligobacteria among the various phyla suggest that metabolic patterns could have since evolved and that metabolic strategies may have converged. The major direct control of oligobacterial activity is the concentration of utilizable nutrients at the surface of the cell. The ability to concentrate many nutrients in this way appears to be cosmopolitan so that successful members of the oligobacteria have coevolved across many genetic lineages.