Abstract
Thermoanaerobacter strains have recently gained interest because of their ability to convert short chain fatty acids to alcohols using actively growing cells. Thermoanaerobacter thermohydrosulfuricus strain AK152 was physiologically investigated for its ethanol and other alcohol formation. The temperature and pH optimum of the strain was 70 °C and pH 7.0 and the strain degraded a variety of compounds present in lignocellulosic biomass like monosaccharides, disaccharides, and starch. The strain is highly ethanologenic, producing up to 86% of the theoretical ethanol yield form hexoses. Strain AK152 was inhibited by relatively low initial substrate (30 mM) concentration, leading to inefficient degradation of glucose and levelling up of all end-product formation. The present study shows that the strain produces alcohols from most of the tested carboxylic acids, with the highest yields for propionate conversion to propanol (40.7%) with kinetic studies demonstrating that the maximum conversion happens within the first 48 h of fermentation. Various physiological tests were performed to maximize the acid conversion to the alcohol which reveals that the optimum pH for propionate conversion is pH 6.7 which affords a 57.3% conversion. Kinetic studies reveal that propionate conversion is rapid, achieving a maximum conversion within the first 48 h of fermentation. Finally, by using 13C NMR, it was shown that the addition of propionate indeed converted to propanol.
Highlights
The sustainable production of small molecular building blocks, such as alcohols is of great interest given the role that these chemicals serve in the production of more complex molecules
DTihsecrumsosainoanerobacter strain AK152 is closely related to Thermoanaerobacter thermohydrosulfuricus and has a siTmhielramr ogarnoawerthobraacntegresatrsaainfuAnKct1io5n2 oisf ctelomspeleyrarteularete(d50t/o70T/7h5eramsocaonmaeproabreadctetor t3h7e/r7m0/o7h8y,drreosspuelcfutirviceulys)and anhdaspaHs(i4m.0il/a7r.0g/8ro.0wvtsh. r5a.5n/g6e.9a–s7a.5f/u9.n2c,trieosnpoefctievmelpye)raalttuhroeu(g5h0/A70K/71552asiscolemssptaorleedratnot3t7o/7h0ig/7h8l,yreaslkpaelcitniveely) coanndditipoHns([47.]0./L7.i0k/e8.m0 avnsy. 5T.h5e/r6m.9o–a7n.5ae/9ro.2b,acrteesrpsepcetcivieesl,ys)traalitnhoAuKg1h52AuKt1il5iz2eissalerassngtoeloefrahnetxotosehsi,gphelnytoasleksa,line dic-oanndditipoonlsy[s7a]c.cLhiakreidmeasn(yFTighueremo2a)n. aCeroombapctaeresdpetcoiems,asntryaicnloAsKel1y52reulatitleizdesTaherramnogaenoaferhoebxaoctseers,sptreaninto,ses, AKdi1-5a2nids phoiglyhslaycecthhaarnidoelosg(Feingiucrper2o)d. uCcoimngpareoduntodm75a%nyocflothselythreeolaretetidcaTlheetrhmaonaonlaeyrioebldactferromstr2a0inm, AMK152 of glucose
Based on the results reported here, it is very likely that carboxylic acid reduction may be responsible for strain AK152 s ability to produce branched-chain alcohols from branched-chain amino acids
Summary
The sustainable production of small molecular building blocks, such as alcohols is of great interest given the role that these chemicals serve in the production of more complex molecules. An attractive route to sustainable alcohol production from waste materials, such as through the bioreduction of inexpensive and abundant carboxylic acids presents a potential alternative for the production of higher chain alcohols. All members of Thermoanaerobacter have a broad substrate spectra, utilizing hexoses, pentoses, disaccharides, sugar alcohols such as mannitol [10], and polysaccharides, such as starch in addition to proteins and amino acids [11], as well as wide tolerance to fermentation conditions, including extremes of pH and temperature. A notable exception is Thermoanaerobacter strain J1, isolated from a hot spring in Iceland, which has high tolerance to high initial substrate loadings and producing ethanol as the dominant fermentation product [12]
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