Biocatalytic pretreatment of rice straw by ligninolytic enzymes produced by newly isolated Micrococcus unnanensis strain B4 for downstream cellulolytic saccharification

[摘要] Rice (Oryza sativa L.) straw is an agriculturalbyproduct of high yield, and its disposal by burninghas detrimental effect on ecosystem. It has potentialas source of fermentable sugars for industrial use;however, it requires effective pretreatment to removelignin. Bacterial enzymes based pretreatment isadvantageous due to their extracellular nature, andtolerance to higher temperature, pH and oxygenlimitation. We herein report screening of lignocellulose degradation environment of vermicompostfor ligninolytic bacteria, and studying role ofMicrococcus unnanensis strain B4 in delignificationof rice straw. The bacterium was capable to degradeacid soluble and insoluble lignin; and producedlignin degrading laccase and peroxidase havingmaximum activity at pH 6.5 and 72 h incubation.Both enzymes exhibited alkaline pH stability, andthermal stability with retention of 100 % activityon pre-incubation at 60 oC for 1h. The enzymes wereused for pretreatment of rice straw using chemicals(acetic acid:hydrogen peroxide) pretreatment asreference. Scanning electron microscopy of pretreated rice straw samples showed alteration inmorphology with exposure of cellulosic components.Enzymatically pretreated rice straw on saccharification by a commercial cellulase yielded about 400mg of reducing sugar per gram, comparable to thatreleased on chemical pretreatment. Hence, pretreatment based on M.unnanensis strain B4 and its ligninolytic enzymes can be an alternative to chemicalpretreatment for saccharification of rice straw tofermentable sugars.

[学科分类] 微生物学和免疫学

[关键词] Laccase;Lignin;Micrococcusunannensis strain B4;Peroxidase;Rice straw;Saccharification