Fatty acid profiling of microbial community during aging of mucilaginous aggregates in the northern Adriatic.

Aggregates differing in size and phytoplankton community composition were sampled in winter/spring 2001 and summer 1997 and 2002 (during mucilaginous event) in the northern Adriatic Sea. The fatty acid profiles (FAME) were determined in aggregates, bacterial population was grown from each aggregate and each bacterial isolate from aggregate's plated cultures. All aggregates irrespective of the season, aggregate size or phytoplankton community composition contained isolates from three distinct groups, with fatty acid profiles corresponding to alpha-Proteobacteria, gamma-Proteobacteria and Cytophaga-Flavobacter (CF) complex but in different relative proportions. Fatty acid profiles of the bacterial population grown from each aggregate revealed either the domination of one group (gamma, alpha or CF) or contribution of more groups (gamma and CF; alpha and CF). Specifically, as the aggregates age a shift in favor of bacteria belonging to CF-complex and corresponding decrease in bacteria similar to that of Proteobacteria occur. During the aggregate aging process and degradation of the mucous matrix, besides bacterial succession, the phytoplankton growth took place inside the aggregates. Such an aging pattern was confirmed through laboratory experiments with aggregates inhabited by the diatom Cylindrotheca closterium.