Changes in bacterial community and sediment characteristics in shrimp ponds

This study investigated the change of bacterial communities and sediment characteristics in the shrimp pond during cultivation period. Sediment samples were collected from 2 shrimp ponds at Nong Suea, Pathum Thani Province, 2 ponds at Ban Pho, Chachoengsao Province, 1 pond at Bang Khla, Chachoengsao Province and 3 ponds in Bang Khun Thian, Bangkok. Sediment characteristics were analyzed using chemical analysis. Bacterial community was examined using a combination of cultured and 16S rDNA PCR-DGGE technique. The identity of bacterial populations was identified by comparing isolated 16S rDNA sequences with the database. The results showed that organic matter was accumulated in all shrimp pond sediment while nitrogen compounds were fluctuated during cultivation. Meanwhile, the concentrations of ammonia and nitrite in several ponds tended to increased with the increasing of bacterial number. Total bacteria count showed that the number of bacteria increased with culture period. The PCR-DGGE results indicated the shifts of bacterial populations with increasing species diversity at the end of cultivation. After cloning, sequencing and comparing 16S rDNA with the database, it was found that the dominant bacteria in the sediment were Pseudomonas, Serratia, Vibrio, Marinobacter, Halomonas, Desulfovibrio and Bacillus. Moreover, many dominant bacteria appeared on DGGE gel were uncultured bacteria. An investigation of nitrogen decomposition and transformation under laboratory condition showed that bacteria in sediment from shrimp pond could decompose organic nitrogen and convert to inorganic nitrogen. This was according to ammonification, nitrification and denitrification processes, respectively. Nitrification process, however, could rapidly occur even the nitrifying bacteria were not the dominant group.