Bacteria associated with a marine planktonic copepod in culture. I. Bacterial genera in seawater, body surface, intestines and fecal pellets and succession during fecal pellet degradation

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Abstract
In laboratory experiments, the bacterial flora of the zooplankton microbial environments seawater, fecal pellets and associated with the external and internal surfaces of the copepod Acartiatonsa (Dana) were examined. The bacteria associated with fecal pellets were dominated by Bacillus spp., Cytophaga/Flavobacterium spp., Vibrio spp. and Pseudomonas spp. The same genera were found in the seawater (0.22 7mu;m filtered) in which the pellets were incubated. The bacteria showed a characteristic growth succession, and the abundance increased several orders of magnitude in the seawater during incubation of the pellets, indicating growth and proliferation based on the disintegrating/degrading fecal pellets. A carbon budget calculation revealed that organic matter from degrading fecal pellets could cover the carbon demand for the growing bacterioplankton. The composition of the bacterial community in the seawater and the fecal pellets also indicated a colonization of the pellets from bacterioplankton. The composition of the bacteria associated with the copepods showed that bacterial genera characterized as surface associated were preferentially associated with fecal pellets, animal surfaces and intestines. This suggests a specific intestinal flora in the cultivated copepods composed of 103 culturable bacteria per intestine (colony-forming units, c.f.u.) or 105 bacteria per intestine (acridine orange direct counts, AODC), possibly colonizing the intestine passively during filtration of algae. The activity of the bacterial communities was examined by the numencal ratio c.f.u.:AODC, where 1–19% of the bacteria were found active, with no significant difference between microbial environments.

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