Structure, diversity, and catabolic potentialities of aerobic heterotrophic bacterial populations associated with continuous cultures of natural marine phytoplankton.

Variations of structure (probable taxonomic generic groups; ecological profiles), diversity (Shannon index, ¯H), and average catabolic potentialities (strain's average exoenzyme equipment, EAI; average carbonaceous compound utilization, UAI) of bacterial populations during two experimental phytoplankton blooms are described and show a certain overall unity. Oligotrophic conditions are characterized by high diversity levels (¯H from 3.60 to 4) and moderate catabolic potentialities (EAI and UAI close to 40%). During phytoplankton exponential growth phase bacteria show an EAI stability, but there is an increase of UAI with maximal values at the beginning of chlorophyll plateau (52-57%) and higher values of diversity (¯H greater than 4). Phytoplankton mortalities appear to cause an EAI increase and a decrease of both UAI and ¯H (1.50 to 2). Vibrio-like organisms seem to be closely related to this period.In spite of these similar patterns, many differences appear between both experiments from a taxonomic point of view, the autumnal population being more diversified than the spring one.The results obtained show the value of simultaneous analysis of these different aspects and of this ecological methodology allowing spatial or temporal comparisons.