P11 Understanding the role of the hfs hydrogenase in Thermoanaerobacterium saccharolyticum
Sunday, July 24, 2016
Grand Ballroom, 5th Fl (Sheraton New Orleans)
A. Eminoğlu*, Recep Tayyip Erdogan University, Rize, Turkey, D. Olson, Dartmouth College, Hanover, NH and L.R. Lynd, Oak Ridge National Laboratory, Oak Ridge, TN
The primary hydrogenase in T. saccharolyticum is called hfs, and it consists of 4 subunits, hfsA, hfsB, hfsC and hfsD.  Previously it has been shown that a complete deletion of all 4 subunits (A, B, C and D) does not increase ethanol production. Deletion of hfsABCD and ldh in combination increased ethanol yield by 44%.  In strains engineered for high ethanol production, spontaneous mutations are often found in one or more of the hfs subunits.  A mutant hfs operon (called hfs*), containing two point mutations from a high-ethanol-producing strain, was re-introduced into the wild-type strain resulting in a 36% increase in ethanol yield.  To better understand the hydrogenase, we deleted each subunit individually.  Deletion of hfsA or hfsB in the wild-type strain increased ethanol yield to ≥89% of the theoretical maximum.  Even in the presence of high cellobiose concentrations (20 g/l ), lactate production was not increased. Also, H2 production was significantly decreased in DhfsA (70%) and in DhfsB (90%), which is highly correlated with acetate production. However, deletion of hfsC and hfsD in the wild-type strain had no substantial effect on fermentation products. Deletion of a single subunit, either A or subunit B (but not C or D), results in ethanol production near the theoretical maximum yield.