Control of Product Formation During Glucose Fermentation by Bacillus macerans

Abstract

The anaerobic fermentation of glucose by Bacillus macerans ATCC 7068 was studied in batch culture with and without pH control. The fermentation was characterized by two distinct metabolic phases. In the primary growth phase, the concentrations of ethanol and acetic acid increased exponentially, and formate was detected as a minor product. The secondary phase was marked by a slowing and eventual cessation of growth, along with the disappearance of formate and acetate, and the appearance of H2, C02, and acetone. Exogenously-added substrates were converted with stoichiometries of 1 formate -+ 1 H2 + 1 C o t , and approximately 2 acetate + 1 acetone. Consumption of > 8 g glucose 1-required exogenous pH control, and acetone formation was strongly pH-dependent. Glucose was fermented by the Embden-Meyerhof pathway. Cell extracts contained pyruvate formate-lyase and formate dehydrogenase activities, but only low pyruvate dehydrogenase activity. A balanced fermentation pathway is presented which is consistent with reaction stoichiometries and [ 14C]glucose labelling data in whole cultures, and with enzyme activities in extracts. The pathway is compared with those of other facultative anaerobes and the acetone-producing Clostridium acetobutylicum.

Ethanol production by a Paenibacillus species isolated from an Icelandic hot spring – Production yields from complex biomass

“…This is not surprising as the oxidation states of these substrates is greater compared to monosaccharides and thus there is less need to direct the electrons produced to NAD + via ethanol production. Ethanol generation by Paenibacillus species has received relatively little attention although Paenibaillus macerans has been shown to produce 1.30 mM ethanol per mol of glucose (Weimer, 1984a). Strain J2 did not utilize arabinose, mannose, rhamnose, cellobiose, sucrose, lactose, cellulose, CMC, avicel, glycerol, and threonine.…”

“…The most likely reasons for this inhibition are due to lower pH values observed in the experimental bottles with high glucose loadings. Paenibacillus macerans, for example, has been shown to stop carbohydrate fermentation when the pH drops below pH 4.9 (Weimer, 1984a). To look at the relationship between pH and acetate formation these data were plotted together ( Figure 2B) showing that increased acetate formation leads to lower pH at the end of incubation.…”

“…Indeed, for strain J2, hydrogen together with acetate and butyrate production decreased with increasing L/G phases but ethanol production did not increase (Figure 3). The main reason for this could be that the strain may not possess pyruvate ferredoxin oxidoreductase but pyruvate formate lyase as demonstrated in strains of P. macerans (Weimer, 1984a). P. macerans produces 1.3 mol ethanol mol glucose -1 but during kinetic study of the strain a late appearance of hydrogen and disappearance of formate suggest that formate is cleaved to hydrogen and carbon dioxide (Weimer, 1984a).…”

“…The main reason for this could be that the strain may not possess pyruvate ferredoxin oxidoreductase but pyruvate formate lyase as demonstrated in strains of P. macerans (Weimer, 1984a). P. macerans produces 1.3 mol ethanol mol glucose -1 but during kinetic study of the strain a late appearance of hydrogen and disappearance of formate suggest that formate is cleaved to hydrogen and carbon dioxide (Weimer, 1984a). Also, results indicated that the reducing equivalents for ethanol production were not only derived from the oxidation of glucose to pyruvate but also from pyruvate degradation to formate and hydrogen.…”

“…Few reports on the fermentative metabolism of members of Paenibacillus have been reported despite some strains being able to degrade cellulose and other polymeric substrates (Dasman et al 2002, Daane et al 2002. Paenibacillus macerans (formerly Bacillus macerans) has been reported to produce 1.3 mole of ethanol from one mole of glucose (Weimer, 1984a); this species is very versatile even degrading glycerol and deoxyhexoses to 1,2-propanediol (Weimer, 1984b, Gupta et al 2009). …”