BioChem - DOS

Crossing the Thauer limit: rewiring cyanobacterial metabolism to maximize fermentative H2 production

Energy & environmental science

Kumaraswamy, Kenchappa G.; KrishnanPresent address: Department of Biochemistry, University of Alberta, Edmonton, Alberta, T6G2RE, Canada., Anagha; Ananyev, Gennady; ZhangPresent address: Department of Biological Engineering, Synthetic Biology Center, 500 Technology Square NE47-140, Massachusetts Institute of Technology, Cambridge, MA 02139, USA., Shuyi; Bryant, Donald A.; Dismukes, G. Charles

<P>Many cyanobacteria power metabolism during dark anaerobic conditions by the catabolism of glycogen which creates adenylate energy (ATP) and NAD(P)H. The latter can be reoxidized by a reversible NiFe-hydrogenase functioning as a terminal oxidoreductase generating H<SUB>2</SUB> as byproduct. Theoretically, one glucose molecule can yield up to 12 molecules of H<SUB>2</SUB>, although this never happens <I>in vivo</I>. The thermodynamic preference is for glucose catabolism <I>via</I> the Embden-Meyerhof-Parnas (EMP) pathway (henceforth, glycolysis) which restricts the pathway yield below 4 mole H<SUB>2</SUB> per mole glucose (so-called Thauer limit). An alternate route that is not used is the oxidative pentose phosphate shunt (OPP), which theoretically can yield 3-fold more NAD(P)H than glycolysis. Herein, we engineer the cyanobacterium <I>Synechococcus</I> sp. PCC 7002 to redirect glycogen catabolic flux through OPP by deleting the <I>gap1</I> gene for glyceraldehyde-3-phosphate dehydrogenase (GAPDH-1) and stack this with a knock-out mutation of NADH-consuming lactate dehydrogenase (<I>ldhA</I>). The resulting &Delta;<I>gap1</I>&Delta;<I>ldhA</I> double mutant when combined with the elimination of H<SUB>2</SUB> uptake by continuous electrochemical removal of H<SUB>2</SUB> was able to produce 681 &mu;mol H<SUB>2</SUB> per g DW per day, equivalent to 6.4 mole H<SUB>2</SUB> per mole glucose, well beyond the Thauer limit. This achieves the highest <I>in vivo</I> autofermentative H<SUB>2</SUB> production yield of any bacterium, equivalent to 80% of the theoretical maximum of 8 H<SUB>2</SUB> per glucose <I>via</I> OPP, using only photoautotrophically generated glycogen as precursor with full retention of cellular viability. These findings demonstrate the plasticity of central carbon metabolism and the significant potential of metabolic engineering for redirecting carbohydrate catabolism towards hydrogen production in cyanobacteria.</P><P>Graphic Abstract</P><P>Metabolic engineering of cyanobacteria with concomitant electrochemical elimination of H<SUB>2</SUB> uptake increases H<SUB>2</SUB> yield beyond the Thauer limit.<BR/><IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c8ee03606c'/><BR/></P>

2019

The Royal Society of Chemistry

1754-5692

1754-5706

12

3

pp.1035-1045

10.1039/c8ee03606c

http://click.ndsl.kr/servlet/OpenAPIDetailView?keyValue=05787966&target=NART&cn=NART96047810