Production of metabolites from different carbon sources
The synthesis of solvents and acids by T. thermosaccharolyticumGSU5 was analyzed in cultures grown using different substrates in 5 ml tubes, and compared with the type strain of the species, DSM 571. Both strains grew well on several monosaccharides: glucose, xylose, arabinose and galactose, and also on the disaccharides sucrose and cellobiose. They grew slightly more when using fructose that on pentoses and other hexoses, and also showed a modest preference for cellobiose compared to sucrose (despite their specific epithet). In all cases they produced alcohols and acids, but no acetone. Ethanol was the most abundant alcohol, and butanol was also observed in all cultures in lower amounts. Among the acids, butyrate was the most abundant, followed by acetate, with lower amounts of lactate (Figure 3).
The relative production of the metabolites depended on the substrate used, and some differences were observed between the strains. The main product of GSU5 was butyrate in all conditions tested, ranging from 0.93 to 2.07 g/L, while DSM 571 synthesized butyrate as a main product (0.99 to 1.35 g/L) in all cultures except those using glucose and xylose, in which similar amounts of ethanol and butyrate were observed (Figure 3). Both strains produced much more ethanol than butanol. GSU5 produced between 0.12 and 0.73 g/L ethanol and 0.005 to 0.048 g/L butanol, with the highest amount of butanol produced in sucrose. DSM 571 produced between 0.25 and 1.25 g/L ethanol and 0.014 to 0.034 g/L butanol with the highest amount of butanol obtained in glucose.
Strain GSU5 produced 3.2 times more butanol than DSM 571 in sucrose (0.048 vs 0.015 g/L; p<0.05), and also accumulated more butanol than DSM571 in arabinose, while the opposite was observed in fructose and cellobiose, in which strain DSM571 produced more butanol than GSU5. When ethanol production was compared, strain DSM 571 produced a greater concentration of ethanol than GSU5 in all hexoses and in xylose, in which the highest amount was observed (0.98 g/L), while GSU5 accumulated more ethanol in arabinose and with the disaccharides sucrose and cellobiose, with the maximum production in this last carbon source (0.73 g/L).