The occurrence of sulphate reducing bacteria in bottom sediments of selected estuarine ecosystems of South Kerala, and their activities were analyzed in vitro. The study covered three estuaries viz. , Poonthura, Veli and Kadinamkulam of Thiruvananthapuram District. SRB were enumerated using the roll tube technique (modified Hungate method) in Postgate medium. Morphologically distinct colonies were isolated and transferred to Postgate broth in serum vials capped with butyl rubber stopper and aluminium cap assembly. The isolated cultures were used for further characterization and sulphate reduction studies. The viable coimt of SRB corresponded to organic carbon and sulphate concentration of the sediment. Molecular characterization by phylogeny of 1 6SrRNA genes revealed that strain S4 was Citrobacterfiezmdii and S5 was Bacillus tequilensis, the activity of the latter as SRB is hitherto unreported. Nevertheless, both the identified cultures did not belong to the traditional group of SRB (5 proteobacteria). The growth of SRB and sulphate reduction was tested in two carbon sources (ethanol, acetate) and electron acceptors (sulphite, sulphate). When ethanol was used as substrate, both sulphate and sulphite as electron acceptors showed similar range of sulphide production. However, when acetate was used as substrate, sulphate as electron acceptor showed more sulphide production than sulphite. Acetate provided continued growth of C. fi'eundii throughout the incubation period and sulphate reduction was more during decline phase of growth. This study indicates the presence of extremely diverse SRB communities that exhibit geographic patchiness and warrants more research.
展开▼
