Efficient lignin biodegradation triggered by alkali-tolerant ligninolytic bacteria through improving lignin solubility in alkaline solution

Low lignin solubility in aqueous solution is one of the major bottlenecks for lignin biodegradation and bioconversion. Alkaline solution contributes to improving lignin solubility, whereas most microbes can not survive in alkaline conditions. Herein, lignin dissolution behaviors in different pH solutions were systematically investigated, which indicated that solution pH above 10.5 contributed to high solubility of alkali lignin. To match with alkaline lignin aqueous system, several alkali-tolerant ligninolytic bacteria were isolated, most of which are distinct to previously reported ones. Then, the ligninolytic capabilities of these isolates were assessed in different pH conditions by determining their assimilation on alkali lignin, lignin-derived monomers and dimers, their decolorization capabilities, and their lignin peroxidase activities. Thereafter, the underlying ligninolytic and alkali-tolerant mechanisms of Sutcliffiella sp. NC1, an alkalophilic bacterium, was analyzed on the basis of its genome information. The results not only provide valuable information for lignin biodegradation and lignin valorization, but also expand knowledge on alkali-tolerant bacteria.