Harold L. Drake

Utilization of methoxylated aromatic compounds by the acetogen Clostridium thermoaceticum : Expression and specificity of the CO-dependent O-demethylating activity

The aromatic CO-dependent O-demethylating activity of Clostridium thermoaceticum was evaluated. Secondary aromatic substituent groups (-OH, -CO2H, -CH2OH, and -OCH3) were critical to O demethylation. O-demethylating activities and specificities were similar from cells grown at the expense of different methoxylated aromatic compounds; all O-methyl-grown cells catalyzed the same sequential O demethylation of multi-methoxylated compounds, suggesting that a broad specificity O demethylase was involved in O demethylation. In cell-fractionation studies, CO-dependent O demethylation was catalyzed by membrane-associated components.

Carbon monoxide-dependent evolution of hydrogen by the homoacetate-fermenting bacterium Clostridium thermoaceticum

Clostridium thermoaceticum was found to form H2 when cultivated heterotrophically on dextrose under a carbon monoxide (CO) gas phase. In contrast, when cultivated under CO2, only minimal levels of hydrogen were detected. Resting cells from the CO-grown cultures also formed H2 when incubated under CO with dextrose, while a comparative study with resting cells from CO2-grown cultures demonstrated that the CO2-grown cells were not competent in H2 formation when incubated under CO. When dextrose was deleted, CO-cultivated resting cells did not form H2 when incubated under CO.

Bidirectional transformation of aromatic aldehydes by Desulfovibrio desulfuricans under nitrate‐dissimilating conditions

M. PAREKH, H.L. DRAKE AND S.L. DANIEL 1996. Desulfovibrio desulfuricans ATCC 27774 was screened for reactivity against aromatic compounds during lactate‐dependent, nitrate‐dissimilating growth. Only aromatic aldehydes (benzaldehyde, 2‐hydroxybenzaldehyde, 3‐hydroxybenzaldehyde, 4‐hydroxybenzaldehyde, vanillin, iso‐vanillin and o‐vanillin) were reactive and, with the exception of 2‐hydroxybenzaldehyde, were stimulatory to lactate‐dependent growth. Aromatic aldehydes were transformed to their corresponding benzoate and benzyl alcohol derivatives, with the ratio of benzoate‐to‐benzyl alcohol derivatives being dependent upon lactate availability. In presence of lactate, aromatic aldehydes were primarily reduced to their corresponding benzyl alcohol derivatives; in the absence of lactate, aromatic aldehydes were mainly oxidized to their corresponding benzoate derivatives. In the absence of nitrate, 3‐hydroxybenzaldehyde was neither reduced nor oxidized. These results indicate that D. desulfuricans is competent in the bidirectional transformation of aromatic aldehydes under nitrate‐dissimilating conditions and that the direction of transformation (i.e. reduction or oxidation) is regulated by reductant availability.