Showing papers by "I. S. Bright Singh published in 2011"

Isolation and characterization of virulent Aeromonas veronii from ascitic fluid of oscar Astronotus ocellatus showing signs of infectious dropsy.

Abstract: The cichlid oscar Astronotus ocellatus has worldwide commercial value in the pet fish industry because of its early maturation, relatively high fecundity, ability to identify its caretaker and also to alter colouration amongst conspecifics. Pathogenic strains of Aeromonas veronii resistant to multiple antibiotics were isolated from A. ocellatus individuals showing signs of infectious abdominal dropsy. The moribund fish showed haemorrhage in all internal organs, and pure cultures could be obtained from the abdominal fluid. The isolates recovered were biochemically identified as A. veronii biovar sobria and genetically confirmed as A. veronii based on 16S rRNA gene sequence analysis (GenBank accession no. FJ573179). The RAPD profile using 3 primers (OPA-3, OPA-4 and OPD-20) generated similar banding patterns for all isolates. They displayed cytotoxic and haemolytic activity and produced several exoenzymes which were responsible for the pathogenic potential of the isolates. In the representative isolate MCCB 137, virulence genes such as enterotoxin act, haemolytic toxin aerA, type 3 secretion genes such as aexT, ascVand ascF-ascG, and gcat (glycerophospholipid-cholesterol acyltransferase) could be amplified. MCCB 137 exhibited a 50% lethal dose (LD50) of 10(5.071) colony-forming units ml(-1) in goldfish and could be subsequently recovered from lesions as well as from the internal organs. This is the first description of a virulent A. veronii from oscar.

Nitrification in a packed bed bioreactor integrated into a marine recirculating maturation system under different substrate concentrations and flow rates

Abstract: BACKGROUND: A packed bed bioreactor (PBBR) activated with an indigenous nitrifying bacterial consortia was developed and commercialized for rapid establishment of nitrification in brackish water and marine hatchery systems in the tropics. The present study evaluated nitrification in PBBR integrated into a Penaeus monodon recirculating maturation system under different substrate concentrations and flow rates. RESULTS: Instant nitrification was observed after integration of PBBR into the maturation system. TAN and NO2-N concentrations were always maintained below 0.5 mg L−1 during operation. The TAN and NO2-N removal was significant (P < 0.001) in all the six reactor compartments of the PBBR having the substrates at initial concentrations of 2, 5 and 10 mg L−1. The average volumetric TAN removal rates increased with flow rates from 43.51 (250 L h−1) to 130.44 (2500 L h−1) gTAN m−3 day−1 (P < 0.05). FISH analysis of the biofilms after 70 days of operation gave positive results with probes NSO 190 ((β ammonia oxidizers), NsV 443 (Nitrosospira spp.) NEU (halophilic Nitrosomonas), Ntspa 712 (Phylum Nitrospira) indicating stability of the consortia. CONCLUSION: The PBBR integrated into the P. monodon maturation system exhibited significant nitrification upon operation for 70 days as well as at different substrate concentrations and flow rates. This system can easily be integrated into marine and brackish water aquaculture systems, to establish instantaneous nitrification. Copyright © 2011 Society of Chemical Industry