Bioconversion Of Lignin To Microbial Lipid By Mycobacterium Smegmatis LZ-K2

As the second most abundant biopolymer on Earth,lignin is hard to be valorized without pretreatment due to its inherent heterogeneity and recalcitrance.Shortage of non-renewable fossil fuels have created the need to dramatically increase the conversion of biomass,such as lignin,to value-added products.The conversion of lignocellulosic biomass typically involves biomass pretreatment,enzymatic hydrolysis of pretreated biomass,and fermentation.However,the high consumption and secondary pollution were introduced by physicochemical pretreatment for the dependence of stringent conditions and high energy input.Moreover,the bioconversion of lignin without chemical pretreatment will improve the carbon efficiency and reduce the cost of chemical addition.Some bacteria naturally store triacylglycerides(TAG)in cells,which can be utilized as biodiesel precursors.However,most studies focused on the lignin model compounds or lignocellullosic biomass typically involves chemical pretreatment to yield sugar for lipid production.In order to produce a more efficient biodiesel conversion from lignin by one-step,it is necessary to develop efficient bacterium resources in lignin conversion without pretreatment.In this study,a strain named Mycobacterium smegmatis LZ-K2 were isolated,which prefers to degrade lignin rather than cellulose.Its selective ligninolysis provide a potential approach to convert lignin to bio-lipids without pretreatment.Our results showed that the lipid yields by one step lignin conversion with LZ-K2 were similar to conventional methods,such as acid or alkali pretreatments.The study demonstrated that enzyme system and Fenton reaction are the major pathways for lignin depolymerization,which may be the reason why the lignin can be converted without chemical pretreatment by M.smegmatis LZ-K2.In addition,critical lignin degradation enzyme,rather than cellulase and hemicellulase,exists in the genome analysis.Moreover,the genome of LZ-K2 contains enzymes involved in the Fenton reaction,such as glucosemethanol-choline oxidoreductase.The genome analysis indicated that β-ketoadipate pathway about metabolism of aromatic compounds might be applied by LZ-K2 to convert aromatic compounds into acetyl-CoA.Notably,the unique enzymes,such as acetyl CoA carboxylase,of oleaginous microorganism were also found in LZ-K2.The results of proteomics confirmed the analysis of genome.Additionally,fatty acids(C14-C24),especially methyl palmitate(C17:0;38.93%),were accumulated in cells with corn straw culture without chemical treatment.And the lipid yields of LZ-K2 on corn straw medium with alkali pretreatment,acid pretreatment and without chemical pretreatment were 0.083 g/L,0.069 g/L and 0.072 g/L respectively.As far as we know,the discovery is among the first to show that the capability of selective lignin degradation of M.smegmatis LZ-K2 and lipid accumulation from agriculture waste,in particular,without pretreatment.The findings in this study will provide a foundation to comprehensively understand a lignin valorization and novel biological platform in lignin without chemical pretreatment.