Shrimp grow out systems under zero water exchange mode demand constant remediation of total ammonia nitrogen (TAN) and NO 2 −-N to protect the crop. To address this issue, an inexpensive and user-friendly technology using immobilized nitrifying bacterial consortia (NBC) as bioaugmentors has been developed and proposed for adoption in shrimp culture systems. Indigenous NBC stored at 4°C were activated at room temperature (28°C) and cultured in a 2 L bench top fermentor. The consortia, after enumeration by epifluorescence microscopy, were immobilized on delignified wood particles of a soft wood tree Ailantus altissima (300-1500 μm) having a surface area of 1.87 m 2 g − 1. Selection of wood particle as substratum was based on adsorption of NBC on to the particles, biofilm formation, and their subsequent nitrification potential. The immobilization could be achieved within 72 h with an initial cell density of 1 × 10 5 cells mL − 1. On experimenting with the lowest dosage of 0.2 g (wet weight) immobilized NBC in 20 L seawater, a TAN removal rate of 2.4 mg L − 1 within three days was observed. An NBC immobilization device could be developed for on site generation of the bioaugmentor preparation as per requirement. The product of immobilization never exhibited lag phase when transferred to fresh medium. The extent of nitrification in a simulated system was two times the rate observed in the control systems suggesting the efficacy in real life situations. The products of nitrification in all experiments were undetectable due to denitrifying potency, which made the NBC an ideal option for biological nitrogen removal. The immobilized NBC thus generated has been named TANOX (Total Ammonia Nitrogen Oxidizer).
Nitrate reducing potency of 88 bacterial isolates segregated from marine and brackish water nitrifying bacterial consortia (NBC), generated for activation of nitrifying bioreactors, was confirmed by determining the nitrate reducing capability under aerobic conditions as maintained in nitrifying bioreactors. All the isolates had the potential to be used as bio‐augmentors for activating nitrate dissimilation in recirculating aquaculture system. The existence of nitrate reducers with nitrifiers in NBC and in the reactor configuration negates the requirement of integrating anoxic denitrifying system for effective removal of NO3−‐N. Phylogenetic analyses of representative isolates from each cluster of the dendrograms generated based on phenotypic characterization and amplified ribosomal DNA restriction analysis revealed profound diversity of nitrate reducing bacterial flora in the NBC. They were composed of Streptomyces enissocaesilis, Marinobacter sp., Pseudomonas sp., Microbacterium oxydans, Pelagibacterium halotolerans and Alcanivorax dieselolei from marine NBC and Streptomyces tendae, Nesterenkonia sp., Bacillus cereus, Microbacterium oxydans and Brevibacterium sp. from brackish water NBC. The diversity indices of the consortia were calculated using Mega 5.0, primer 7 and VITCOMIC softwares. Marine NBC exhibited higher Shannon wiener diversity and mean population diversity than brackish water NBC. The study delineated higher species richness and diversity in marine NBC than in its brackish water counterpart, a possible reflection of the higher biodiversity of marine systems, and hence, the former is more promising to be used as start‐up cultures for the activation of nitrifying bioreactors after appropriate acclimatization to the desired salinity.
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