Though homoacetogens have been defined as autotrophic anaerobes using acetyl-CoA Wood-Ljungdahl carbon fixation pathway (WLP) for energy conservation

acetate production and biomass formation from CO2

these anaerobes can also utilize organic compounds heterotrophically to produce acetate and form biomass by Embden-Meyerhof-Parnas (EMP) glycolysis. A better understanding of the interrelationship between autotrophy and heterotrophy in homoacetogens will be helpful for acetate biosynthesis from exhaust rich in CO2. However

interaction of the two metabolisms has not been well understood though both of which have been extensively investigated respectively. Blautia coccoides GA-1

a novel homoacetogen strain obtained in a previous study

was introduced to the present research and the interrelationship between autotrophy and heterotrophy in the strain was investigated by sub-culturing with glucose and (or) H2/CO2 (vol

4:1) as carbon source (s). The results showed that the cell production of strain GA-1 in H2/CO2 cultures was too low to be sub-cultured after the 5th generation due to the energy produced was very limited in WLP. On the contrary

the strain could grow very well in glucose cultures and could be sub-cultured steadily. However

the autotrophic capability of the subcultures decreased by generations

even lost since the 7th generation in 1000 mg·L-1 glucose cultures. This may be resulted in: (1) the competition for Coenzyme A (CoA) between the autotrophic WLP and the heterotrophic EMP glycolysis

(2) ATP produced in the strain used up for biosynthesis rather for acetate synthesis from H2/CO2

(3) inhibition of lower pH less than 5.5 to the activity of hydrogenase

(4) negative effect of the lower pH on intracellular balance of NADH/NAD+. In mixotrophic cultures with H2/CO2 and 200 mg·L-1 glucose as co-carbon sources

strain GA-1 could not only be sub-cultured steadily but also keep autotrophic activity well in the generations with a specific acetate production of about 2.16 g·(g dry cell)-1 from H2/CO2.