Morphological study of marine bacterial capsules: implications for marine aggregates

Abstract

The morphological variation in bacterial capsules found in suspended and sinking particles from the open ocean is examined. The capsules consist of matrices of mucopolysaccharides that remain attached to and extend the cell surface. Transmission electron microscope images of several distinct and recurring morphs are presented. Capsule abundance relative to total numbers of bacteria is significantly higher in sinking particles (up to 80% of total bacteria present) than in fine suspended particles (up to 20%). Discrete fecal pellets and minipellets are inadequate sources of the capsules captured by sediment traps. Alternatively, the data and previous observations indicate that the bacterial capsules are removed from the fine suspended-particle phase in association with macroaggregates, or marine snow. The combined properties of the bacterial capsules with their extensive open matrices of attached sticky polymers suggest a high aggregation efficiency.