In addition, aeration is always used in intensive shrimp ponds to improve water quality and increase shrimp yields, and all the 16 shrimp ponds were provided with mechanical continuous aeration, particu- larly at the end of culture. This is the reason why the AAPB such as R. denitrificans and R. elongatum detected from all water samples; and R. denitrificans was detected from most sediment samples. The AAPB are aerobic and carry out anoxy- genic photosynthesis by capturing energy from light using ple organic compounds as a carbon source for their growth utin et al., 2007: Tang et al., 2009). In contrast, a greater diversity of the PNSB was found in the sediment samples than in the water samples with a higher detection rate of the pufM gene; this is because the sediment conditions in shrimp ponds are enriched with organic matter with only a limited amount oxygen and far from the sunlight, but the PNSB also grow in dark conditions using fermentation (mhoff, 2001: Karr t al., 2003). Hence, PNSB could compete better with the PSB in the bottom of the ponds because light is limiting for photosynthesis. The high percentage of pufM amplified "uncul- tured' bacteria in both sample types indicated that there could be many species of purple bacteria and AAPB in the shrimp pond environment that were uncultured species. In addition, it was possible that the extracted DNA template of these spe- cies were at low levels, thus resulting in a reduced specificity for amplification of the pufM gene, so any incomplete sequence was classified as an "uncultured' bacterium.