|Structure of the newly identified lignin-degrading enzyme from Rhodococcus. Copyright: Lindsay Eltis and Michael Murphy. Click to enlarge.|
Researchers funded by the Biotechnology and Biological Sciences Research Council (BBSRC)-led Integrated Biorefining Research and Technology (IBTI) Club have identified an enzyme in bacteria which is important in breaking down lignin. This research, carried out by teams at the Universities of Warwick and British Columbia, could make sustainable sources of biofuels, such as woody plants and the inedible parts of crops, more economically viable.
The researchers identified the gene for breaking down lignin in a Rhodococcus jostii—a polychlorinated biphenyl-degrading soil bacterium whose genome has been sequenced. Although such enzymes have been found before in fungi, this is the first time that they have been identified in bacteria. Because the bacterium’s genome has already been sequenced, it could be modified more easily to produce large amounts of the required enzyme. In addition, bacteria are quick and easy to grow, so this research raises the prospect of producing enzymes which can break down lignin on an industrial scale.
Bioinformatic analysis reveals two unannotated peroxidase genes present in the genome of R. jostii RHA1 with sequence similarity to open reading frames in other lignin-degrading microbes. They are members of the Dyp peroxidase family and were annotated as DypA and DypB, on the basis of bioinformatic analysis.
...DypB has a significant role in lignin degradation in R. jostii RHA1, is able to oxidize both polymeric lignin and a lignin model compound, and appears to have both MnII and lignin oxidation sites. This is the first detailed characterization of a recombinant bacterial lignin peroxidase.
...Considering that the in vitro activity of recombinant DypB with lignocellulose is quite modest, we suspect that there is a group of oxidative enzymes used by the host for lignin metabolism, of which DypB is only one member. Nevertheless, it is the first recombinant bacterial lignin peroxidase to be kinetically characterized. The identification of DypB and further bacterial lignin-degrading enzymes, and their availability in recombinant form, will provide valuable new reagents for the conversion of lignocellulose to biofuels and renewable chemicals.—Ahmad et al.
Lignin is important in making plants sturdy and rigid but, because it is difficult to break down, it makes extracting the energy-rich sugars used to produce bioethanol more difficult. Fast-growing woody plants and the inedible by-products of crops could both be valuable sources of biofuels but it is difficult to extract enough sugar from them for the process to be economically viable. Using an enzyme to break down lignin would allow more fuel to be produced from the same amount of plant mass.
For biofuels to be a sustainable alternative to fossil fuels we need to extract the maximum possible energy available from plants. By raising the exciting possibility of being able to produce lignin-degrading enzymes from bacteria on an industrial scale this research could help unlock currently unattainable sources of biofuels. By making woody plants and the inedible by-products of crops economically viable the eventual hope is to be able to produce biofuels that don’t compete with food production.—Professor Timothy Bugg, University of Warwick, who led the team
The team at Warwick has been collaborating with colleagues in Canada at the University of British Columbia who have been working to unravel the structure of the enzyme. They hope next to find similar enzymes in bacteria which live in very hot environments such as near volcanic vents. Enzymes in these bacteria have evolved to work best at high temperatures meaning they are ideally suited to be used in industrial processes.
The Integrated Biorefining Technologies Initiative (IBTI) club aims to provide a means to combine relevant academic expertise to work on innovative, multidisciplinary, scientific areas of relevance to industry. An integral feature of the club’s operation will be the delivery of efficient mechanisms to facilitate the dissemination of research outcomes to club members and support effective networking and community building between academic groups and the companies involved.
The club currently has 10 company members: Biocaldol Ltd; BP Biofuels UK Ltd; British Sugar Plc; Croda Enterprises Ltd; Green Biologics Ltd; HGCA; InCrops; KWS UK Ltd; Syngenta Ltd; and TMO Renewables Ltd.
The researchers were also supported by the UK’s Engineering and Physical Sciences Research Council EPSRC); a paper on their work appears in the 14 June issue of the ACS journal Biochemistry.
Mark Ahmad, Joseph N. Roberts, Elizabeth M. Hardiman, Rahul Singh, Lindsay D. Eltis, Timothy D. H. Bugg (2011) Identification of DypB from Rhodococcus jostii RHA1 as a Lignin Peroxidase. Biochemistry50 (23), 5096-5107 doi: /10.1021/bi101892