Community composition of marine and brackish water ammonia-oxidizing consortia developed for aquaculture application.

To mitigate the toxicity of ammonia in aquaculture systems, marine and brackish water ammonia-oxidizing bacterial consortia have been developed and are used for activation of nitrifying bioreactors integrated to recirculating aquaculture systems. To shed more light on to these biological entities, diversity of both the consortia were analyzed based on random cloning of 16S rRNA gene and ammonia-oxidizing bacterial specific amoA gene sequences. The dendrograms of representative clones on the basis of amplified ribosomal DNA restriction analysis generated 22 and 19 clusters for marine and brackish water nitrifying consortia, respectively. Phylogenetic analysis demonstrated the presence of various autotrophic nitrifiers belonging to α-, ß- and γ-Proteobacteria, anaerobic ammonia oxidizers, heterotrophic denitrifiers, Bacteroidetes, and Actinobacteria. Distribution patterns of the organisms within the two consortia were determined using the software Geneious and diversity indices were investigated using Mega 5.0, VITCOMIC and Primer 7. The abundance of ammonia oxidizers was found in the order of 2.21 ± 0.25 × 109 copies/g wet weight of marine consortium and 6.20 ± 0.23 × 107 copies/g of brackish water consortium. Besides, marine ammonia-oxidizing consortium exhibited higher mean population diversity and Shannon Wiener diversity than the brackish water counterparts.

Isolation and characterization of broad spectrum bacteriophages lytic to Vibrio harveyi from shrimp farms of Kerala, India.

UNLABELLED: Of 33 phages isolated from various shrimp farms in Kerala, India, six were segregated to have broad spectrum lytic efficiency towards 87 isolates of Vibrio harveyi with cross-infecting potential to a few other important aquaculture pathogens. They were further tested on beneficial aquaculture micro-organisms such as probiotics and nitrifying bacterial consortia and proved to be noninfective. Morphological characterization by transmission electron microscopy (TEM) and molecular characterization by RAPD and SDS-PAGE proved them distinct and positioned under Caudovirales belonging to Myoviridae and Siphoviridae. SIGNIFICANCE AND IMPACT OF THE STUDY: In sustainable aquaculture, application of antibiotics is prohibited to manage vibriosis, including the one caused by Vibrio harveyi. In lieu of antibiotics, an eco-friendly alternative method, phage therapy, is recommended here. To facilitate the same, a set of six broad spectrum V. harveyi phages, as cocktail, has been constituted and characterized based on morphological traits and by employing molecular tools. These phages were also found to infect other aquaculture pathogens belonging to Vibrio and Aeromonas. Subsequent to in vivo trials, they can find application in shrimp hatcheries as prophylactics and therapeutics.