Salinity and DOC Influence the Distribution of Free-living and Particle-attached Aerobic Anoxygenic Phototrophic Bacteria in the Qinghai–Tibetan Lakes

Aerobic anoxygenic phototrophic bacteria (AAPB) are widespread and play an important role in carbon cycling in the lakes of the Qinghai–Tibetan Plateau. However, little is known about how free-living and particle-attached AAPB distribute with salinity in the Qinghai–Tibetan lakes. In the present study, the abundance and diversity of free-living and particle-attached AAPB were investigated in seven Qinghai–Tibetan lakes with salinity ranging from freshwater to almost saturation (1.2 g L−1 241.1 g L−1). An integrated approach was employed including pufL-M gene (encoding the photosynthetic reaction center of AAPB) based quantitative polymerase chain reaction (qPCR) and PCR-cloning phylogenetic analysis. The qPCR data showed that the ratio between particle-attached and free-living AAPB was positively correlated (R2 = 0.73, p < 0.01) with increasing salinity. The phylogenetic analysis of pufL-M gene showed that the composition of AAPB population varied with salinity in the studied Qinghai–Tibetan lakes. These results suggested that salinity may be the important factor shaping the AAPB distribution in the studied Qinghai–Tibetan lakes, and AAPB may be adapted to the harsh conditions in the Qinghai–Tibetan lakes by attaching to particles.