Isolation, identification and characterisation of lignocellulolytic bacteria from mangrove roots

Abstract

Globally, 998 million tonnes of agricultural waste is disposed into landfills per year and Malaysia contributes 1.2 million tonnes of the amount. The waste consists of lignocellulosic biomass, a chainlike sugars called cellulose and hemicellulose embedded in a woody material called lignin, which could be converted into biofuel. Enzymes secreted by microorganisms are needed for the conversion of these materials into biofuels. One of good sources to find the microorganisms that are able to degrade the lignocellulosic materials is mangrove. It is a rich environment containing plenty of decayed plant materials, thus it could be a potential resource of highly productive and diverse microbial community. In this study, five bacterial strains have been isolated from mangrove roots collected in Tanjung Piai, Johor. From the lignocellulolytic screening, CN4, CN7 and CN10 showed positive results for cellulose degradation, CN10 and CN12 for xylan degradation, and CN20 for lignin degradation. Strain CN10 was selected for further investigation due to its abilities to degrade both cellulose and xylan. Gram-staining performed showed that CN10 is a Gram-positive rod-shaped bacterium. Based on 16S rRNAgene sequence analysis, the selected strain was identified as Exiguobacterium sp. CN10. Growth profile was carried out at 35°C, pH 7 and 5% (w/v) salt using tryptic soy broth as medium. The effect of temperature, pH and salinity on cellulose and xylan degradation using crude enzyme of CN10 were investigated. For cellulose degradation, the optimal temperature, pH and salinity for strain CN10 were 50°C, pH 8.0 and 12% (w/v) respectively. For xylanase activity, the optimal temperature and pH for the strain were also at 50°C and pH 8.0, while the optimal salinity was at 10% (w/v) salt. Collectively, the findings suggested that the strain CN10 may have a great potential in the lignocellulosic biomass degradation which could be of great commercial value.