Isolation of a plasmid harbouring cellulolytic bacterial strain from decomposing rice straw

Abstract

Although rice straw can be utilized as an organic fertilizer most of the farmers are compelled to discard this valuable source of nutrients without any use because of its slow rate of decomposition which obstructs the subsequent operations in the field. Organisms with high cellulolytic activity can be employed to mitigate this problem by accelerating the rate of decomposition of rice straw. Although both fungi and bacteria are capable of synthesizing cellulase enzymes, less work on such bacteria has been reported compared to that of fungi. In this study six cellulolytic bacterial strains associated with partially decomposed rice straw were isolated, identified and their cellulolytic activity was compared. Two isolates identified as Pseudomonas sp. and Acinetobacter sp. showed high level of endo-1,4-ß glucanase (carboxymethylcellulase) activity. Amount of glucose released by saccharification of cellulose was also high with these two strains. The susceptibility of these two strains to antimicrobial agents was tested with various antibiotics at different concentrations. The Acinetobacter sp tolerates high level of ampicillin i.e.100 µg /ml and Pseudomonas sp was susceptible to all tested antibiotics. The strain with antibiotic resistance, presumed to carry plasmids was examined for the presence of plasmid by plasmid DNA isolation and subsequent gel electrophoresis. This Acinetobacter sp carries a plasmid that generate eight (8) fragments when digested with Hind III .The plasmid DNA digested with Pst I produces a smear on the gel suggesting the presence of many Pst I sites. There is a dearth of information on presence of plasmids in cellulolytic bacteria. The Acinetobacter strain isolated in this study is useful to investigate whether the cellulolytic function is encoded by a plasmid gene.