Sep
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A Break in the Lignin Wall
September 3, 2010 | 2 Comments
Lignin is a part of the molecular structure that keeps plants together. In its role it’s quite strong and resistant to breakdown. For producing alcohol products getting past the lignin is a major chemical and cost obstacle.
The lignin molecules are clumped around the target sugar molecules, forming a barrier the alcohol producing microbes often can’t penetrate. The lignin could first be exposed to heat and steam or caustic acids and bases to break it down. These extra steps make the process more expensive and often generate hazardous waste. The process consumes time, materials and energy all adding to the facility cost and operating expense – the reasons behind ethanol not being on schedule with U.S. policy to take transport market share.
A team of researchers from the University of Florida and the biotechnology company Chesapeake-PERL Inc. of Savage, Md. have isolated two enzymes termites use to break up lignin. They’re reporting in a paper published online in the journal Insect Biochemistry and Molecular Biology, a determination that enzymes found in termite salivary tissues may be able to accomplish the same task, and at room temperature. If so and the costs are not high, the enzymes work quickly and require no massive facility costs – a breakthrough could be at a hand.
The study follows more than two years of work to identify nearly 7,000 genes associated with the termite gut. The researchers are wading through the genes to identify which ones are associated with enzymes that could be useful, and they are hopeful that many more such exciting discoveries are yet to come. That makes for a bit of surprise a salivary enzyme turned up further down tract and has been identified and sourced back up the tract.
University of Florida entomologist Mike Scharf, who led the research said, “Once we figure out the best way to integrate this sort of enzyme into the process, it could drop the cost of producing cellulosic ethanol significantly.”
James Preston, a UF microbiology professor who studies enzymes in bacteria that break down plant material said, “This is definitive and original research that could realistically be a significant contribution to green energy. It’s this kind of work that keeps pushing cellulosic ethanol toward practicality.”
From the study abstract: two gut laccase isoforms (RfLacA and RfLacB) were sequenced from the termite Reticulitermes flavipes. Phylogenetic analyses comparing translated R. flavipes laccases to 67 others from prokaryotes and eukaryotes indicate that the R. flavipes laccases are evolutionarily unique. Alignments with crystallography-verified laccases confirmed that peptide motifs involved in metal binding are 100% conserved in both isoforms. Laccase transcripts and phenoloxidase activity were most abundant in symbiont-free salivary gland and foregut tissue, verifying that the genes and activities are host-derived.
Using a baculovirus-insect expression system, the two isoforms were functionally expressed with histidine tags and purified to near homogeneity. ICP-MS (inductively coupled plasma – mass spectrometry) analysis of RfLacA identified bound metals consisting mainly of copper ( 4 copper molecules per laccase protein molecule and 3 per histidine tag) with lesser amounts of calcium, manganese and zinc. Both recombinant enzyme preparations showed strong activity towards the lignin monomer sinapinic acid and four other phenolic substrates.
By contrast, both isoforms displayed much lower or no activity against four melanin precursors, suggesting that neither isoform is involved in integument formation. Modification of lignin alkali by the recombinant RfLacA preparation was also observed. These findings provide evidence that R. flavipes gut laccases are evolutionarily distinct, host-derived, produced in the salivary gland, secreted into the foregut, bind copper, and play a role in lignocellulose digestion. These findings contribute to a better understanding of termite digestion and gut physiology, and will assist future translational studies that examine the contributions of individual termite enzymes in lignocellulose digestion.
Somewhere between the study and the university press release the jump was made to alcohol fuels. One can bet with confidence that the biotechnology company Chesapeake-PERL wouldn’t bother unless the target was to get a lower cost lignin process. Chesapeake-PERL hasn’t updated the company site as of this writing so perhaps in time the clarity of the research to product path will become clearer.
Even in a technically specific explanation the science looks good. Termites have been a fascinating potential source of information about taking wood fiber apart and getting useful products for decades. Now genetic testing and steady determined research is getting some results.
Scharf said at the end of the pres release quite sanguinely, “We still have a long way to go before we’re finished. But, in the meanwhile, we can start putting what we have discovered to good use.”
Just so, professor Scharf, and congratulations.
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jellies!
Great site. A lot of useful information here. I’m sending it to some friends!