Ecological Process Studies On Functional Bacterial Groups In The Sea

Heterotrophic bacterioplankton are important members in marine ecosystems, including various bacterial groups, and play a critical role in carbon and energy cycles. What kinds of organisms are present in a system and what function of the system as a whole and how the individual microbial types contribute are the main goal of marine ecology study. This study focused on a newly recognized functional bacterial group—Aerobic Anoxygenic Phototrophic Bacteria (AAPB). We investigated distribution pattern of AAPB along environmental gradients in the China Seas and North Pacific, studied temporal-spatial variations and correlations with environmental variables, and summed up the niche of AAPB in marine ecosystem. The main outcomes include:1) Established an accurate quantitative technique—Time-series observation based cyanobacteria-calibrated Infrared Epifluorescence Microscopy (TIREM).2) The abundance of AAPB and their rate to total bacteria decreased along trophic gradient from estuary to open water. Namely, the relative abundance of AAPB was higher in eutrophic waters than in oligotrophic waters.3) There were significant positive relationship between abundance and rate of AAPB and Chl. a concentration, suggesting the dependence of AAPB on dissolved organic carbon from phytoplankton.4) The seasonal variation of AAPB was smaller than that of heterotrophic bacteria, and AAPB's percentage of total bacteria was highest in winter.AAPB are a bacterial group based on function. Phylogenetically, they are mainly affiliated to Alpha and Beta-proteobacteria, and some Gamma-proteobacteria-like AAPB also were found newly. We combined microautoradiography and fluorescence in situ hybridization (Micro-FISH) to study the succession of bacterioplankton community and contribution of various phylogenetic groups to the activity of total communities along environmental gradient. Our results from the South China Sea (SCS) showed the preponderant contribution of beta-proteobacteria in freshwater and alpha-proteobacteria in saltwater to abundance and total bacterial production along the salinity gradient from the Pearl River estuary to the open water. Gamma-proteobacteria were always a minor component in SCS, while the Cytophaga-Flavobacterium cluster was a significant component in both marine and freshwater systems. Analysis at the single-bacterial group level showed a statistically significant correlation between abundance and leucine-uptake activity for beta-proteobacteria, suggesting that the abundance of beta-proteobacteria in the study area was controlled by growth-related processes.