Engin­eer Con­verts Yeast Cells into ​‘Sweet Crude’ Biofuel

Assist­ant pro­fess­or Hal Alp­er, in the Cock­rell School’s McK­etta Depart­ment of Chem­ic­al Engin­eer­ing, along with his team of stu­dents, cre­ated the new cell-based plat­form. Giv­en that the yeast cells grow on sug­ars, Alp­er calls the bio­fuel pro­duced by this pro­cess ​“a renew­able ver­sion of sweet crude.” The research­ers’ plat­form pro­duces the highest con­cen­tra­tion of oils and fats repor­ted through fer­ment­a­tion, the pro­cess of cul­tur­ing cells to con­vert sug­ar into products such as alco­hol, gases or acids. This work was pub­lished in Nature Com­mu­nic­a­tions on Jan. 20. The UT Aus­tin research team was able to rewire yeast cells to enable up to 90 per­cent of the cell mass to become lip­ids, which can then be used to pro­duce biod­ies­el. ​“To put this in per­spect­ive, this lip­id value is approach­ing the con­cen­tra­tion seen in many indus­tri­al bio­chem­ic­al pro­cesses,” Alp­er said. ​“You can take the lip­ids formed and the­or­et­ic­ally use it to power a car.” Since fatty mater­i­als are build­ing blocks for many house­hold products, this pro­cess could be used to pro­duce a vari­ety of items made with pet­ro­leum or oils — from nylon to nutri­tion sup­ple­ments to fuels. Bio­fuels and chem­ic­als pro­duced from liv­ing organ­isms rep­res­ent a prom­ising por­tion of the renew­able energy mar­ket. Over­all, the glob­al bio­fuels mar­ket is expec­ted to double dur­ing the next sev­er­al years, going from $82.7 bil­lion in 2011 to $185.3 bil­lion in 2021. ​“We took a start­ing yeast strain of Yar­rowia lipoly­t­ica, and we’ve been able to con­vert it into a fact­ory for oil dir­ectly from sug­ar,” Alp­er said. ​“This work opens up a new plat­form for a renew­able energy and chem­ic­al source.” The bio­fuel the research­ers for­mu­lated is sim­il­ar in com­pos­i­tion to biod­ies­el made from soy­bean oil. The advant­ages of using the yeast cells to pro­duce com­mer­cial-grade biod­ies­el are that yeast cells can be grown any­where, do not com­pete with land resources and are easi­er to genet­ic­ally alter than oth­er sources of bio­fuel. ​“By genet­ic­ally rewir­ing Yar­rowia lipoly­t­ica, Dr. Alp­er and his research group have cre­ated a near-com­mer­cial biocata­lyst that pro­duces high levels of bio-oils dur­ing car­bo­hydrate fer­ment­a­tion,” said Lon­nie O. Ingram, dir­ect­or of the Flor­ida Cen­ter for Renew­able Chem­ic­als and Fuels at the Uni­ver­sity of Flor­ida. ​“This is a remark­able demon­stra­tion of the power of meta­bol­ic engin­eer­ing.” So far, high-level pro­duc­tion of bio­fuels and renew­able oils has been an elu­sive goal, but the research­ers believe that industry-scale pro­duc­tion is pos­sible with their plat­form. In a large-scale engin­eer­ing effort span­ning over four years, the research­ers genet­ic­ally mod­i­fied Yar­rowia lipoly­t­ica by both remov­ing and over­ex­press­ing spe­cif­ic genes that influ­ence lip­id pro­duc­tion. In addi­tion, the team iden­ti­fied optim­um cul­tur­ing con­di­tions that dif­fer from stand­ard con­di­tions. Tra­di­tion­al meth­ods rely on nitro­gen star­va­tion to trick yeast cells into stor­ing fat and mater­i­als. Alper’s research provides a mech­an­ism for grow­ing lip­ids without nitro­gen star­va­tion. The research has res­ul­ted in a tech­no­logy for which UT Aus­tin has applied for a pat­ent. ​“Our cells do not require that star­va­tion,” Alp­er said. ​“That makes it extremely attract­ive from an industry pro­duc­tion stand­point.” The team increased lip­id levels by nearly 60-fold from the start­ing point. At 90 per­cent lip­id levels, the plat­form pro­duces the highest levels of lip­id con­tent cre­ated so far using a genet­ic­ally engin­eered yeast cell. To com­pare, oth­er yeast-based plat­forms yield lip­id con­tent in the 50 to 80 per­cent range. How­ever, these altern­at­ive plat­forms do not always pro­duce lip­ids dir­ectly from sug­ar as the UT Aus­tin tech­no­logy does. Alp­er and his team are con­tinu­ing to find ways to fur­ther enhance the lip­id pro­duc­tion levels and devel­op new products using this engin­eered yeast. This research was fun­ded by the Office of Nav­al Research Young Invest­ig­at­or Pro­gram, the DuPont Young Pro­fess­or Grant and the Welch Found­a­tion under grant F‑1753. Source: Uni­ver­sity of Texas