New under­stand­ing of one of nature’s best biocata­lysts for bio­fuels production

Pro­du­cing fuels from plants and oth­er renew­able sources requires break­ing down the chem­ic­al cel­lu­lose; a major can­did­ate to drive, or cata­lyze, this stub­born chem­ic­al is a ubi­quit­ous microor­gan­ism called Clostridi­um ther­mo­cel­lum that works well in hot envir­on­ments without oxy­gen. Research­ers found that C. ther­mo­cel­lum uses a pre­vi­ously unknown mech­an­ism to degrade cel­lu­lose, in addi­tion to oth­er known degrad­a­tion mech­an­isms. This dis­cov­ery helps explain C. ther­mo­cel­lum​’s super­i­or abil­ity to digest bio­mass and demon­strates the highly diverse strategies evolved in nature for bio­mass con­ver­sion. Research­ers are using the study’s find­ings to devel­op optim­al sys­tems for break­ing down plant mat­ter to pro­duce bio­fuels and biobased chem­ic­als. Ligno­cel­lu­losic bio­mass is the largest source of organ­ic mat­ter on Earth, mak­ing it a prom­ising renew­able feed­stock for pro­du­cing bio­fuels and chem­ic­als. Cur­rently, how­ever, the main bot­tle­neck in bio­fuel pro­duc­tion is the low effi­ciency of cel­lu­lose con­ver­sion, which leads to high pro­duc­tion costs. To date, C. ther­mo­cel­lum is the most effi­cient microor­gan­ism known for sol­u­bil­iz­ing ligno­cel­lu­losic bio­mass. Its high cel­lu­lose diges­tion cap­ab­il­ity has been attrib­uted to the organism’s effi­cient cel­lu­lases con­sist­ing of both a free enzyme sys­tem and a tethered cel­lu­lo­somal sys­tem, where mul­tiple car­bo­hydrate act­ive enzymes are organ­ized by primary and sec­ond­ary scaf­fold­ing pro­teins to gen­er­ate large pro­tein com­plexes attached to the bac­teri­al cell wall. Recently, U.S. Depart­ment of Energy BioEn­ergy Sci­ence Cen­ter (BESC) research­ers dis­covered that C. ther­mo­cel­lum also expresses a type of cel­lu­lo­somal sys­tem that is not bound to the cell wall, a ​“cell‐​free” cel­lu­lo­somal sys­tem. Research­ers believe the cell‐​free cel­lu­lo­some com­plex func­tions as a ​“long-range” cel­lu­lo­some because it can dif­fuse away from the cell and degrade poly­sac­char­ide sub­strates dis­tant from the bac­teri­al cells. This dis­cov­ery reveals that C. ther­mo­cel­lum util­izes not only all the pre­vi­ously known cel­lu­lase degrad­a­tion mech­an­isms (cel­lu­lo­somes and free enzymes), but also a new cat­egory of scaf­fol­ded enzymes not attached to the cell. This unex­pec­ted find­ing explains C. thermocellum’s super­i­or per­form­ance on bio­mass, demon­strat­ing that nature’s strategies for bio­mass con­ver­sion are not yet fully under­stood and could provide fur­ther oppor­tun­it­ies for micro­bi­al enzyme dis­cov­ery and engin­eer­ing efforts. This work was sup­por­ted by the BioEn­ergy Sci­ence Cen­ter (BESC). BESC is a U.S. Depart­ment of Energy (DOE) Bioen­ergy Research Cen­ter sup­por­ted by the Office of Bio­lo­gic­al and Envir­on­ment­al Research with­in DOE’s Office of Sci­ence. A por­tion of this work also was sup­por­ted by the United States – Israel Bin­a­tion­al Sci­ence Found­a­tion, Jer­u­s­alem, Israel; Israel Sci­ence Found­a­tion (ISF; grant num­ber 1349), Israeli Cen­ter of Research Excel­lence (I – CORE; num­ber 152/11); European Uni­on NMP.2013.1.1 – 2: Cel­lu­lo­somePlus Pro­ject 8 num­ber 604530; and the ERA – IB Con­sor­ti­um (EIB.12.022) Fiber­Fuel.

Ori­gin­al publication

Xu, Q., et al. Dra­mat­ic per­form­ance of Clostridi­um ther­mo­cel­lum explained by its wide range of cel­lu­lase mod­al­it­ies. Sci­ence Advances, 2016 DOI: 10.1126/sciadv.1501254 Source: U.S. Depart­ment of Energy