Title: Deletion of nfnAB in Thermoanaerobacterium saccharolyticum and Its Effect on Metabolism

Abstract

NfnAB catalyzes the reversible transfer of electrons from reduced ferredoxin and NADH to 2 NADP⁺. The NfnAB complex has been hypothesized to be the main enzyme for ferredoxin oxidization in strains of Thermoanaerobacterium saccharolyticum engineered for increased ethanol production. NfnAB complex activity was detectable in crude cell extracts of T. saccharolyticum. In this paper, activity was also detected using activity staining of native PAGE gels. The nfnAB gene was deleted in different strains of T. saccharolyticum to determine its effect on end product formation. In wild-type T. saccharolyticum, deletion of nfnAB resulted in a 46% increase in H₂ formation but otherwise little change in other fermentation products. In two engineered strains with 80% theoretical ethanol yield, loss of nfnAB caused two different responses: in one strain, ethanol yield decreased to about 30% of the theoretical value, while another strain had no change in ethanol yield. Biochemical analysis of cell extracts showed that the ΔnfnAB strain with decreased ethanol yield had NADPH-linked alcohol dehydrogenase (ADH) activity, while the ΔnfnAB strain with unchanged ethanol yield had NADH-linked ADH activity. Deletion of nfnAB caused loss of NADPH-linked ferredoxin oxidoreductase activity in all cell extracts. Significant NADH-linked ferredoxin oxidoreductase activity was seen in allmore » cell extracts, including those that had lost nfnAB. This suggests that there is an unidentified NADH:ferredoxin oxidoreductase (distinct from nfnAB) playing a role in ethanol formation. The NfnAB complex plays a key role in generating NADPH in a strain that had become reliant on NADPH-ADH activity. Importance: Thermophilic anaerobes that can convert biomass-derived sugars into ethanol have been investigated as candidates for biofuel formation. Many anaerobes have been genetically engineered to increase biofuel formation; however, key aspects of metabolism remain unknown and poorly understood. One example is the mechanism for ferredoxin oxidation and transfer of electrons to NAD(P)⁺. The electron-bifurcating enzyme complex NfnAB is known to catalyze the reversible transfer of electrons from reduced ferredoxin and NADH to 2 NADP⁺ and is thought to play key roles linking NAD(P)(H) metabolism with ferredoxin metabolism. Finally, we report the first deletion of nfnAB and demonstrate a role for NfnAB in metabolism and ethanol formation in Thermoanaerobacterium saccharolyticum and show that this may be an important feature among other thermophilic ethanologenic anaerobes.« less

Authors:

Lo, Jonathan ^[1]; Zheng, Tianyong ^[1]; Olson, Daniel G. ^[2]; Ruppertsberger, Natalie ^[2]; Tripathi, Shital A. ^[3]; Guss, Adam M. ^[4]; Lynd, Lee R. ^[5]

---

+ Show Author Affiliations

1. Dartmouth College, Hanover, NH (United States). Dept. of Biological Sciences; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC)
2. Dartmouth College, Hanover, NH (United States). Thayer School of Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC)
3. Total New Energies USA, Inc., Emeryville, CA (United States)
4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC)
5. Dartmouth College, Hanover, NH (United States). Dept. of Biological Sciences; Dartmouth College, Hanover, NH (United States). Thayer School of Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC)

Publication Date:

Mon Jun 29 00:00:00 EDT 2015

Research Org.:

Dartmouth College, Hanover, NH (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1265625

Grant/Contract Number:  

AC05-00OR22725; 4000115284

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Bacteriology

Additional Journal Information:

Journal Volume: 197; Journal Issue: 18; Journal ID: ISSN 0021-9193

Publisher:

American Society for Microbiology

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES