Abstract:
Bacterial community in nitrification and denitrification reactors (NR and DNR) for aquaculture was studied with two similar cylinder-shape bioreactors (14 L) packed with plastic bioballs. The experiment was conducted in two trials, each trial consisted of two similar reactors assigned as NR and DNR. For NR, the reactor was continuously aerated to create an aerobic condition for nitrifying bacteria while in DNR was set to anoxic condition by a short bubbling of nitrogen gas. After proper condition was settled up, the results showed that NR and DNR can perform nitrogen treatment by either nitrificaiton or denitrification processes. In the first trial, although the experimental period was 60 days, the duration that nitrification (in NR) or denitrification (in DNR) occured was only the last 10 days. The results from bacterial analysis in the last day using SEM and PCR-DGGE of 16S rDNA showed that bacterial composition in both reactor was similar. Number of bands in DGGE gel illustrated that there was at least 9 species of bacteria growing in the reactor. Two of those bacteria could be identified as that Methylophaga marina and Marinobacter sp. In the second trial, proper conditions for NR and DNR reactors were successfully set up since the starting day and prolong throughout 8 weeks of the experiment. Protein analysis and SEM pictures showed that bacteria in DNR increased rapidly during the experiment while bacteria in NR seemed to have very slow growth rate. From at least 29 species of bacteria found in the starting water obtained from shrimp culture tank, as indicated by 29 DGGE bands, there was only 8 species of bacteria found in NR and DNR after 8 weeks of the experiment. Among those bacteria, 5 species were found only in NR , 5 species were found only in DNR and 3 species were found in both NR and DNR reactors. Identification of bacterial species found in the reactor by comparing 16S rDNA sequence with the BLASTN database found that Cytophaga-Flavobacterium-Bacteroides (CFB) group bacterium was commonly found in both reactors. With NR, the dominant bacteria were possibly Alpha-proteobacterium, CFB group bacterium, Methylobacterium sp. while the dominant bacteria in DNR were Bacteroidetes bacterium, CFB group bacterium, Pseudomonas sp. or Uncultured Colwellia sp.and Desulfobulbus sp.