No abstract

Enzymes synthesized by the gut microbiome are recognized as vital for assisting host metabolism. This study was conducted to screen and identify bacterial isolates with enzyme-producing abilities from the intestine of milkfish Chanos chanos.Overall, 114 isolates were collected, of which 58% showed clear zones indicating various enzyme activities via plate-based assays. Specifically, 65 isolates were amylolytic, 1 isolate was cellulolytic, and 18 isolates exhibited both activities. The two most promising isolates-CC8 and CC27-were further subjected to spectrophotometric enzyme assays to determine their amylase, cellulase and protease activities. Results showed that amylase, cellulase and protease activities (6.00 ± 0.01, 0.52 ± 0.02 and 18.62 ± 0.16 U mg −1 protein, respectively) were higher in CC8 than in CC27. Using 16S rRNA gene sequencing, the isolates were putatively identified as Vibrio sp. and Bacillus cereus respectively. At a suspension (mL) to feed (g) ratio of 3:25, dietary supplementation of putative probiotics was carried out to evaluate the growth performance, survival and enzymatic activities of juvenile Nile tilapia Oreochromis niloticus. Results revealed that probiotic-supplemented fish exhibited better growth performance-final average body weight, weight gain, specific growth rate and feed conversion ratio-along with increased intestinal enzymatic activities compared with the control (p < 0.05). Survival rates ranged from 80% to 90% and were statistically similar in all treatments (p > 0.05). This study concludes that the application of Vibrio sp. CC8 and Bacillus cereus CC27, supplemented either in monostrain or multistrain preparation, can promote growth and enzymatic activities in juvenile Nile tilapia.

We examined the effectiveness of cocopeat and rice hull powder obtained from agricultural wastes as biocarriers for an oil-degrading bacterial consortium. Scanning electron microscopy revealed colonization and strong attachment of bacterial cells on the surface of both carriers. Results of a 60-day in vitro seawater bioremediation trial showed significant oil reduction and high cultivable bacterial counts in treatments augmented with the carrier-attached bacterial consortia compared to treatments supplemented with the same consortium in free living and encapsulated forms. Significant degradations in both aliphatic and aromatic fractions were obtained in treatments augmented with carrier-immobilized consortia. The developed immobilized cells showed sustained activities and viabilities during storage for six months. Results of this study demonstrated that inexpensive waste materials can be utilized as biocarriers of an oil-degrading consortium and that immobilization on biocarriers can enhance the bioremediation of oil-contaminated seawater.

Bacterial communities in sediments underneath milkfish cages and adjacent off‐cage areas in Bolinao, Lingayen Gulf, West Philippine Sea were characterized using PCR‐denaturing gradient gel electrophoresis to assess influence of the fish farming to the sediments. The sediments in the fish cage (FC) area showed anoxic conditions [redox potential of −165 to −213 mV and acid‐volatile sulphide‐sulphur (AVS‐S) of 0.55–1.88 mg g−1 (dry weight)] compared to the relatively oxic off‐cage area [redox potential of 72–81 mV and AVS‐S of 0.09–0.14 mg g−1 (dry weight)]. The composition of the microbial populations revealed influence of the fish feed sedimentation with higher dominance of putative sulphate‐reducing bacteria (SRB) in the FC area. Compositions of the bacterial taxa showed dominance of the Bacteroidetes group and Deltaproteobacteria. The results suggest that the fish feeds created a new suitable environment, in which reductive microorganisms such as SRB, ferric‐ion‐reducing bacteria and nitrate‐reducing bacteria can thrive. Organic load from the feed and quantity of its leftover constituents may be the key factors that influence the structure of the bacterial community in the sediments of the milkfish farms.

The physicochemical properties and bacterial community in sediments of Lake Shiraishi, a lake with brackish water, were characterized to elucidate the influence of oyster farming and seawater and freshwater inflow. Physicochemical analyses suggested the marine origin of the sediment at the mouth of the lake, while higher organic matter load and the resultant anaerobic, reductive condition of the sediments of the inner part were observed. The bacterial community in the sediments reflects these sediment environments: the bacterial community in the vicinities of oyster farms included sulfate-reducing bacteria (SRB) , although sulfur-oxidizing bacteria (SOB) were found at all the sampling sites. In addition, similarity of the band profiles obtained with 16S ribosomal RNA gene (16S rDNA) -denaturing gradient gel electrophoresis (DGGE) decreased in proportion to the distance from the mouth of the lake to the oyster farms in the inner part. This study was able to characterize the microbial community shift in brackish lake sediments with an oyster aquaculture system through the molecular fingerprinting technique, DGGE, in relation to their physicochemical characteristics.