as stated in the introduction, the pufM gene that we used to study the diversity of PNSB in water and sediment samples collected from the sixteen shrimp pond sites was also present in other groups of APB so it was not specific for PNSB Using the pufM gene primers, bands were detected after DGGE in 13 water samples (Fig. 1A) and 10 sediment sam ples (Fig. 1B).