Biochemical mechanisms of bacterial utilization of dissolved and particulate organic matter in the upper ocean

Dissolved and particulate organic matter (DOM, POM) in the ocean is one of the largest pools of reduced carbon on earth; it is about the same size as the atmospheric carbon pool. The chemical composition of this pool and the mechanisms by which it is produced and consumed by organisms are poorly understood. The decomposition process does not necessarily occur in Redfield ratio, and therefore uncouples the carbon and nitrogen cycles. Understanding the decomposition process is critical to understanding the oceanic carbon cycle and quantifying carbon transport by advection and sedimentation.; Enzymatic hydrolysis is a crucial first step in bacterial utilization of polymeric DOM. Bacterial ectoenzymes were studied in the subtropical Pacific, in the equatorial Pacific and in Antarctica. Leucine aminopeptidase and {dollar}alpha{dollar}- and {dollar}beta{dollar}-glucosidase appear to be ubiquitous in seawater and marine particles. These enzymes exhibit similar K{dollar}rmsb{lcub}m{rcub}{dollar}'s in different regions of the ocean, suggesting broad cross-habitat homology, but show adaptation to in situ temperature in each region. Glucosidases show greater specificity than peptidases. Variation in the relative activities of these enzymes indicates significant seasonal and geographic variation in rates of utilization of different components of DOM. {dollar}beta{dollar}-glucosidase activity is much greater in the equatorial Pacific than in the other environments studied, and is low in relation to leucine aminopeptidase in Antarctica. Leucine aminopeptidase expression by Antarctic bacterioplankton is regulated by availability of particular amino acids, notably histidine, and may indicate widespread auxotrophy for these compounds.; Particle associated bacterial communities show assemblages of ectoenzymes and temperature responses of those enzymes distinct from those of free-living bacteria; consistent patterns are observed among the various types of particles. Zooplankton fecal pellets appear to be a minor component of sinking particle flux in the subtropical Pacific. Acidic mucopolysaccharides are abundant in sinking particles, and rates of hydrolysis of these compounds are low. Hydrolytic enzymes and exopolysaccharides of bacteria provide a mechanism for decoupling the carbon and nitrogen cycles in the decomposition process which can produce a net flux of carbon across the thermocline in a region expected to be a net sink for atmospheric CO{dollar}sb2.{dollar}...