A new cellulose-producing bacterium, Rhodococcus sp. MI 2: screening and optimization of culture conditions.

A total of 59 bacterial strains were isolated from ripe fruits and vegetables and tested for their ability to produce cellulose. Only one identified as Rhodococcus sp. MI 2 based on its taxonomic characteristics and 16S rDNA sequence analysis. The glucose was the only product of digestion by cellulase confirmed by TLC and reversed phase HPLC. Rhodococcus sp. MI 2 produced significantly more cellulose with the SH medium containing glucose than with the coconut juice medium. Rhodococcus sp. MI 2 initially produced 3.91 ± 0.091, 2.20 ± 0.090 and 0.19 ± 0.051 g/L/6 days cellulose under static, agitated and stirred conditions, respectively, whereas A. xylinum 998 produced 1.17 ± 0.065, 1.34 ± 0.115 and 0.12 ± 0.046 g/L/6 days cellulose under the same conditions, respectively. The optimum culture conditions for cellulose production in SH medium were room temperature (25 °C), a 5% (v/v) inoculum, peptone 0.7%, yeast extract 0.9%, and sucrose 1.5%, at a pH of 3.5. The cellulose yield was increased by adding 0.5% CaCO(3) to the SH medium with sucrose but added agar had no effect. The cellulose yield under optimum and static conditions was increased about twice, from 3.7 to 7.4 g/L/14 days.