Rex in Caldicellulosiruptor bescii: Novel regulon members and its effect on the production of ethanol and overflow metabolites

Abstract

Rex is a global redox‐sensing transcription factor that senses and responds to the intracellular [ NADH ]/[ NAD + ] ratio to regulate genes for central metabolism, and a variety of metabolic processes in Gram‐positive bacteria. We decipher and validate four new members of the Rex regulon in Caldicellulosiruptor bescii ; a gene encoding a class V aminotransferase, the HydG FeFe Hydrogenase maturation protein, an oxidoreductase, and a gene encoding a hypothetical protein. Structural genes for the NiFe and FeFe hydrogenases, pyruvate:ferredoxin oxidoreductase, as well as the rex gene itself are also members of this regulon, as has been predicted previously in different organisms. A C. bescii rex deletion strain constructed in an ethanol‐producing strain made 54% more ethanol (0.16 mmol/L) than its genetic parent after 36 hr of fermentation, though only under nitrogen limited conditions. Metabolomic interrogation shows this rex‐ deficient ethanol‐producing strain synthesizes other reduced overflow metabolism products likely in response to more reduced intracellular redox conditions and the accumulation of pyruvate. These results suggest ethanol production is strongly dependent on the native intracellular redox state in C. bescii , and highlight the combined promise of using this gene and manipulation of culture conditions to yield strains capable of producing ethanol at higher yields and final titer.

Carbon monoxide-dependent transcriptional changes in a thermophilic, carbon monoxide-utilizing, hydrogen-evolving bacterium Calderihabitans maritimus KKC1 revealed by transcriptomic analysis

“…2 and Table 3). Moreover, kor genes are upregulated in Thermococcus onnurineus under CO conditions, suggesting the possible involvement of Kor in carbon fixation (Moon et al 2012), whereas the GS/GOGAT cycle is a redox-buffering system involving the consumption of NAD(P)H in Caldicellulosiruptor bescii and Clostridium thermocellum (Sander et al 2015(Sander et al , 2019. It is possible that the enzymatic cycle involving Kor, GOGAT, and GS would assimilate carbon and nitrogen using excessive reducing equivalents from CO.…”

Metabolic engineering strategies for consolidated production of lactic acid from lignocellulosic biomass

“…LA production is generally considered as a sink for electrons derived from sugar catabolism. For this reason, it especially competes with other metabolic pathways that consume reducing equivalents such as production of alcohols (e.g., ethanol and butanol) or H 2 and, more in general, is affected by the redox balance of the cell . Recently, improvement of LA production through engineering the transcriptional promoter of ldh gene has been reported in Caldicellulosiruptor bescii , a hyperthermophilic anaerobic cellulolytic bacterium .…”

“…Targets of Rex generally include genes involved in energy conversion, redox metabolism, glycolysis, fermentation, and NAD biosynthesis . Successful deletion of rex gene has been reported in the hyperthermophilic anaerobic bacterium C. bescii and in T. saccharolyticum . C. bescii ∆ rex metabolic profile indicated a more reduced intracellular redox status and increased accumulation of a number of catabolites including LA (Table ) .…”

“…Successful deletion of rex gene has been reported in the hyperthermophilic anaerobic bacterium C. bescii and in T. saccharolyticum . C. bescii ∆ rex metabolic profile indicated a more reduced intracellular redox status and increased accumulation of a number of catabolites including LA (Table ) . Deletion of rex in T. saccharolyticum deregulated the expression of ADH genes adhE and adhA leading to a more than twofold increase in ethanol yield but LA yield was reduced (Table ) .…”

Genomic and physiological analyses reveal that extremely thermophilicCaldicellulosiruptor changbaiensisdeploys unique cellulose attachment mechanisms

“…Further discoveries on the capabilities of these thermostable enzymes include the unique mode of action used by the central cellulase, CelA, [8], synergistic activity in ionic liquid optimized enzyme mixtures [45,46] and the creation of designer cellulosomes from Caldicellulosiruptor catalytic domains [29]. Development of a genetics system for Caldicellulosiruptor bescii [14,16] has also expanded the scope of work with this genus, including metabolic engineering [10,12,13,50] and catalytic improvement [18,30,32,31,34,33].…”