Particle capture by marine bacteria

In aquatic environments large numbers of submicron particles are generally present, and their turnover and fate are of considerable ecological importance in geochemical cycles. Efficient degradation of submicron particles can be attained if the particles are retained on the surfaces of bacterial cells rather than remaining suspended in the aqueous phase. We hypothesized that some bacterial groups possess particle-capture (PC) ability. To verify this hypothesis, we took 2 approaches. First, paramagnetic particles were added to natural seawater samples to separate out bacterial groups with PC capabilities. Method development was carried out in combination with community structure analysis of the separated bacteria by denaturing gradient gel electrophoresis (DGGE) and multidimensional scaling (MDS). Bacterial groups recovered by this new approach were different from either the representative ones in the original seawater sample or large particle associated bacterial groups. Second, atomic force microscopy was used to directly observe the submicron particles within natural bacterial populations. The number of cells retaining submicron particles was high in the inner part of Tokyo Bay and at depths of 500 to 2000 m in the open ocean. We concluded that there are bacterial groups in natural seawater that possess PC ability and we successfully collected these cells using the new paramagnetic particle method presented here.