Distinct distribution pattern of abundance and diversity of aerobic anoxygenic phototrophic bacteria in the global ocean.

Aerobic anoxygenic phototrophic bacteria (AAPB) are an important bacterial group with capability of harvesting light energy, and appear to have a particular role in the ocean's carbon cycling. Yet the significance of AAPB relative to total bacteria (AAPB%) in different marine regimes are still controversial, and variation trend of genetic diversity of AAPB along environmental gradients remains unclear. Here we present the first comprehensive observation of the global distribution of AAPB in the Pacific, Atlantic and Indian oceans, revealing a general pattern of high abundance of AAPB and AAPB% in coastal waters than oceanic waters. The Indian Ocean contained relatively high AAPB% compared with the other two oceans, corresponding to the high primary production in this region. Both abundance of AAPB and AAPB% were positively correlated with the concentration of chlorophyll a, while the diversity of AAPB decreased with increasing chlorophyll a values. Our results suggest that AAPB abundance and diversity follow opposite trends from oligotrophic to eutrophic regimes in the ocean.