Influence Of The Isolated Probiotic Bacteria On The Water Quality

In the present global crisis for food and production costs increase has put pressure on international community and governments to ensure sufficient food supply for growing population. Thus, aquaculture shows a way to meet the growing demand for seafood or fresh water food, and to meet current challenges relating to the ongoing globalization of trade, intensification and progress in technological innovations for food production, diversification of aquaculture, changes in ecological systems and human behaviour, including a greater awareness to protect biodiversity, public health, and the environment. These challenges will lead to increased attention for improving aquaculture practices, and will become an important alternative to over exploitation and modification of aquatic ecosystems caused by capture fisheries. The use of probiotics can potentiate the benefits of this activity because, as presented in this thesis based on obtained results, it offers viable alternatives for the generation of a higher-quality livestock product.

The laboratory studies proved that the isolated bacteria were having considerable probiotic ability and the molecular and phylogenetic analysis proved that the identified bacteria do not belong to any prawn pathogenic group. In vitro studies proved that the isolated probiotic bacteria restricted to WSSV induced CPE in the BHK 21 cell lines.

From the field studies it was proved that the isolated probiotic bacteria were capable of surviving in the pond ecosystem. The reports of water quality variable analysis showed that the isolated probiotic bacteria did not show any significant difference in the temperature, salinity, transparency and pH parameters when compared to the control. The levels of D. O were significantly higher in the probiotic treated ponds than the control pond, total alkalinity was marginally higher in the probiotic treated ponds than in the control pond during initial phases of experiment but it increased gradually in the control ponds with increase in culture duration. The results of the TAN clearly indicated that the levels of TAN were higher in the control ponds than the probiotic treated ponds, the levels of TAN decreased significantly with increase in the culture duration. The nitrites concentration was found to be similar in all ponds at the starting of the experiment which gradually showed a significant decrease in the probiotic treated ponds compared to the control pond. This reflects the higher levels of nitrates in the probiotic treated ponds than the control ponds.

The phosphates level analysis showed a significant increase in the phosphates in the probiotic treated ponds than the control pond. Microbial analysis of the THB showed higher THB count in both control and probiotic treated ponds with significant increase in the probiotic treated ponds. The total Vibrio count was found higher in the control ponds than the probiotic treated ponds. The results from the water quality variable analysis indicated the beneficiary effect of the isolated probiotic bacteria in the pond ecosystem. The results of the growth and survival rates of the prawn showed a significant increase in body weight of the animal and the survival rate in the probiotic treated ponds than the control ponds, this indicated that the isolated probiotic bacteria were capable of inducing a positive effect on the prawn health.

• Isolated bacteria were having considerable probiotic properties.
• Molecular sequencing of the probiotic strains revealed that the isolated probiotic bacteria belong to genera Bacillus and Lactobacillus.
• BLAST and phylogenetic analysis of the above strains showed that they do not belong to any pathogenic group of the species.
• Cell culture studies showed that the identified bacteria are not cytotoxic to the cell lines.
• In vitro studies of the probiotic bacteria showed that they are capable of restricting the WSSV infection in the cell lines which need further studies at molecular level.
• The field studies indicated that the isolated probiotic bacteria can successfully work in the pond environment and they did not show any negative effect on the pond parameters.
• The probiotic bacteria did not show any detrimental effect on the prawn survival and growth.

In the present study, we have successfully isolated probiotic isolates of host origin, which are non-pathogenic, acid- and bile tolerant, capable to adhere to the gut epithelial tissue, modulate immune responses and influence the metabolic activities of the prawn gut and also these probiotics isolates produce antimicrobial substances. Although several probiotics are already available in the market which have beneficial role in prawn culture, the novelty of the isolated new probiotic isolates are having beneficial effect on the prawn and also capable of restricting the WSSV induced CPE in the in vitro studies.

Finally, it is concluded that the isolated bacteria were capable of exerting probiotic properties and antiviral property in restricting the WSSV infection in in vitro studies and the field studies of the four probiotic bacterial isolates (VVRANU -1, 2, 3, 4 ) confirmed that they can be safely applied to the prawn culture ponds.

The future plan of work in continuation of the present work is to carry out research relating to probiotics resistance to antibiotics and the chances of transmission of genetic elements to other microorganisms in the fish GIT and their transmission to humans when consuming the aquaculture product. In addition studies of microbial ecology in aquaculture systems correlating microbial communities (microorganisms in the water and in the GIT of aquatic species) with animal growth and its relationship to the water quality were also the part of the future plan.