ORIGINAL ARTICLE Isolation from coconut retting effluent of Bacillus cereus TC-2 antagonistic to pathogenic Vibrios Aswathy Gopalakrishnan Heineining Nair & Maria Thason Birdilla Selva Donio & Vijaya Raghavan Thanga Viji & Mariavincent Michaelbabu & Thavasimuthu Citarasu Received: 26 May 2010 / Accepted: 3 December 2010 / Published online: 29 December 2010 # Springer-Verlag and the University of Milan 2010 Abstract Antagonistic Bacillus cereus TC-2 (GenBank: GU939624.1), isolated from coconut retting effluent in Rajakkamangalam, Tamilnadu, South India, effectively controlled the important aquatic pathogen Vibrio sp. 16S rRNA gene sequencing and analysis of phylogenetic relationships using a clustering algorithm revealed that this strain was closely related to B. cereus strain CMBLBT-5. Growth of B. cereus TC-2 was optimized in different growth media and with different concentrations of NaCl, and was found to grow well in tryptic soy broth and 2% NaCl in nutrient broth medium. In vivo antagonistic experiments were performed against Vibrio harveyi and Vibrio parahaemolyticus in a shrimp culture tank. The Bacillus count increased significantly (P <0.05) and Vibrio counts decreased at different times following inoculation. Antagonistic correlation analysis revealed that the relation- ships linking B. cereus and V. harveyi and V. para- haemolyticus in terms of in vivo antagonism were significant (P <0.05). Keywords Antagonism . Probiotic . Pathogenic Vibrio sp. . Bacillus cereus Introduction Bacterial diseases are a major cause of mortality in shrimp larviculture (Wyban and Sweeney 1991). Vibrios are one of the most important pathogens for reared aquatic organisms such as penaeid shrimps (Lightner 1993). Vibriosis causes serious problems in the shrimp aquaculture industry and, in order to combat this problem, a large amount of antibiotics are used. As a result, the bacteria have developed increased resistance to all commonly used antibiotics. Thus, current treatment of microbial diseases in shrimps/fishes has become rather difficult, non-effective and costly, as well as posing a serious environmental hazard (Dixon 1991). Recently, the theory of biocontrol has been applied to aquaculture. Many researchers have attempted to use some kind of probiotics in aquaculture systems (Gram et al. 1999). The prophylactic use of probiotics instead of antibiotics would help improve the health and zootechnical performance of cultured fish and shrimp, while simulta- neously avoiding the deleterious side-effects of antibiotics and chemicals (Wyban and Sweeney 1991). Probiotics— naturally beneficial bacteria—are now well accepted and used widely in shrimp aquaculture, and potentially have one or more beneficial function for aquaculture producers, such as (1) water and pond bottom sediment quality are improved, leading to less stress on shrimps and thus improved health; (2) effluent water is cleaner, thus environmental impact is low; (3) pathogenic bacteria and their virulence can be controlled, and the overall microbial ecosystem managed; (4) use of antibiotics is avoided, thus halting the increase in virulence and pathogenicity seen in aquatic bacterial pathogens due to the overuse of anti- biotics, and minimizing the risk of multiple antibiotic resistance; (5) stimulation of the shrimp immune system; and (6) improved gut flora, and hence lower disease incidence and increased food assimilation. The present study focuses on the isolation and characterization of Bacillus sp. with probiotic properties from coconut retting and tannery effluents. The controlling efficiency of this A. G. H. Nair : M. T. B. S. Donio : V. R. Thanga Viji : M. Michaelbabu : T. Citarasu (*) Centre for Marine Science and Technology, Manonmaniam Sundaranar University, Rajakkamangalam, Kanyakumari, Tamilnadu 629502, India e-mail: citarasu@gmail.com Ann Microbiol (2011) 61:631–637 DOI 10.1007/s13213-010-0183-4