Copepod fecal pellet (fp) dissolved organic matter is consumed by free-living bacteria, while particulate matter is degraded by bacteria packed inside the fp (‘internal’) or attached to the fp surface after colonization from the environment (external). This study analyzed the contribution of ‘internal’ and external fp bacteria to the active bacterial community associated with the fp from 2 copepod species, Paramphiascella fulvofasciata and Platychelipus littoralis, during 60 h of fp aging in seawater. Despite early colonization (within 20 to 40 h), fp enrichment by seawater bacteria, as deduced from RNA-based DGGE after 60 h, was limited. In contrast, ‘internal’ bacteria showed high phylotype richness. The majority of ‘internal’ bacterial phylotypes persisted on aged fp and together represented half of the active bacterial community. Food source strongly impacted ‘internal’ bacterial diversity, though the exact origin of fp ‘internal’ bacteria, as either undigested food-associated bacteria or as copepod gut bacteria, could not be unambiguously determined. ‘Internal’ bacteria of fresh fp showed a high functional diversity (based on Biolog assays) to which Vibrio sp. contributed significantly. In terms of bacterial diversity and functional potential, degradation of copepod fp by ‘internal’ bacteria is equally as important as degradation by bacteria which colonize fp from the outside. |
