COMMUNITY STRUCTURES OF HETEROTROPHIC BACTERIA OF COPEPOD FECAL PELLETS

The total and heterotrophic bacterial microflora of gut and fecal pellets of the copepod Temora stylifera was studied in the coastal zone of the northwestern Mediterranean basin. Digestive tracts and feces were always found to contain bacteria. With mean values close to 10(11) cells ml-1 and 10(10)) colony-forming units (CFU) ml-1, both total and heterotrophic communities found in fecal pellets largely exceeded the corresponding bacterial microflora observed in surrounding seawater (10(5) cells ml-1 and 10(3) CFU ml-1). In the same way, the frequency of dividing cells and mean cell volumes increased, respectively, from 3% and 0.12 mum3 in seawater to >6% and 0.24 mum3 in fecal pellets. The bacterial community structure was investigated by carrying out 29 morphological and biochemical tests on 147 isolated strains. Although Pseudomonas was always the most frequently encountered genus, the bacterial communities found in copepod fecal pellets clearly differ from those inhabiting seawater. Vibrio species, which were not detected in seawater microflora, were always present in fecal pellet communities. The close correspondence observed between the potential metabolic characteristics of the fecal bacterial communities isolated from a subantarctic deposit feeder (Mytilus edulis) and from zooplankton in this Mediterranean study suggests that the fecal community differentiation is an even more general feature.