My­codiesel

This is the fourth (and fi­nal) post for this year's Week of the Fungi on STC, a spo­radic un­der­tak­ing. This an­nual fes­ti­val is our way to hail the start of the fall mush­room col­lect­ing sea­son in parts of our home ter­ri­tory (the north­ern hemi­sphere).

by Elio

Huge amounts of money and ef­fort are go­ing into mak­ing au­to­mo­tive fu­els us­ing bi­o­log­i­cal processes, but a fully sat­is­fac­tory an­swer is not yet at hand. Well, fungi may come to the res­cue. Stro­bel et al. found that a fun­gus called Glio­cla­dium ro­seum ac­tu­ally makes a com­plex mix­ture of volatile hy­dro­car­bons and de­riv­a­tives that re­sem­ble those found in diesel fu­els. Not only that, this fun­gus de­com­poses cel­lu­lose with­out need­ing any help. It sounds just right, but be­fore you talk to your bro­ker about your Exxon Mo­bile stock, read on.

Glio­cla­dium ro­seum. Source

This fun­gus, a some­what atyp­i­cal mem­ber of its species, was found in a North­ern Patag­on­ian rain­for­est liv­ing as an en­do­phyte of the tree Eu­cryphia cordi­fo­lia. Now, what are en­do­phytic fungi? They are be­nign in­hab­i­tants of healthy plants and are quite com­mon. En­do­phytic fungi are adroit chemists and make a large num­ber of bioac­tive sec­ondary metabo­lites. The most fa­mous among these is the an­ti­cancer drug taxol, which is widely used in treat­ment. In­ci­den­tally, taxol can be iso­lated from both the plant and its fungi, sug­gest­ing the hor­i­zon­tal trans­fer of genes be­tween them.

G. ro­seum cul­ture plate. Source

The prob­lem with turn­ing G. ro­seum into a fuel ma­chine is that it grows slowly and its rate of pro­duc­tion is far from over­whelm­ing. How­ever, who is to say that fur­ther work on this and other strains may not lead to sig­nif­i­cant im­prove­ments in pro­duc­tion.

There may even be more to the story, as fungi may have par­tic­i­pated in mak­ing pe­tro­leum and its prod­ucts. To let the au­thors ex­plain:"In view of this work, per­haps it is not un­rea­son­able to spec­u­late that some hy­dro­car­bons in the earth's up­per man­tle may have arisen via the fermen­ta­tion of plant ma­te­r­ial by fungi un­der con­di­tions of li­mited oxy­gen. The en­do­phytic mi­crobes may be the first ones in­volved in the dis­in­te­gra­tion and uti­liza­tion of plant ma­te­r­ial since, by de­f­i­n­i­tion, they are lo­cated in the plant tis­sues at the time of the demise of the plant."

How did these in­ves­ti­ga­tors come upon this un­usual find­ing? What were they look­ing for? You may well find out by lis­ten­ing to a pod­cast in which Dr. Stro­bel talks about that.

Merry com­ments

When Strobel's pa­per was pub­lished last year, it was en­thu­si­as­ti­cally touted as re­as­sur­ance that bio­fuel so­lu­tions are on the near hori­zon that will seem­lessly re­place fos­sil fu­els and re­lated pe­trochemicals. (Google "my­codiesel" and pick from the ~40,000 hits.) "Fill 'er up with my­codiesel" was the cry. While un­doubt­edly many bio­fuel op­tions will prove use­ful at some scales, in some lo­cales, at some point in time, sig­nif­i­cant is­sues arise when con­tem­plat­ing meet­ing the world's cur­rent en­ergy needs in this fash­ion.

Let's as­sume for the sake of ar­gu­ment that, in­deed, Stro­bel or oth­ers can grab the genes en­cod­ing the my­codiesel meta­bolic path­way, en­gi­neer them into a tractable mi­crobe, and set up large-scale pro­duc­tion. Among the many points that could be ques­tioned, I'll fo­cus on just one: the car­bon in­put re­quired. Stro­bel has a ready an­swer: the fun­gus can use cel­lu­lose. "That's the most com­mon or­ganic mol­e­cule on earth," he said. "It's all around us, every­where."

In­put could be grown as crops, which would po­ten­tially im­pact food sup­plies and costs, and could also in­crease green­house gas emis­sions. Or we could use agri­cul­tural or log­ging "wastes," thus ac­celerating the min­ing of our soils lead­ing to fur­ther re­duc­tions in pro­duc­tiv­ity. Again, it is a mat­ter of scale.

To put this in per­spec­tive, con­sider how much of the pho­to­syn­thetic out­put of ter­res­tial ecosys­tems we al­ready are us­ing ­– in ad­di­tion to our con­sump­tion of prior pri­mary pro­duc­tion in the form of fos­sil fu­els. Cur­rently, best es­ti­mates of HANPP (hu­man ap­pro­pri­a­tion of net pri­mary pro­duc­tion) stand a bit above 20%, with some oft-quoted val­ues reach­ing as high as 40%. "Peo­ple use this ma­te­r­ial di­rectly or in­di­rectly, it flows to dif­fer­ent con­sumers and de­com­posers than it oth­er­wise would, or it is lost be­cause of hu­man-caused changes in land use." (Source) "This is a re­mark­able level of co-op­tion for a species that rep­re­sents roughly 0.5% of the to­tal het­erotroph bio­mass on Earth."

The take home les­son here, stated in the most re­strained and diplo­matic of terms by Haberl: "An ob­vi­ous im­pli­ca­tion of HANPP is that growth in the amount of bio­mass used by hu­mans for their so­cio-eco­nomic me­tab­o­lism must be en­vis­aged with cau­tion."