This 1988 study investigated how oxygen availability affects the respiratory enzymes and cytochromes produced by Mycobacterium phlei. Researchers grew cultures under aerobic (high oxygen) and low oxygen tension conditions, then measured enzyme activities and analyzed cytochrome composition. Under aerobic conditions, M. phlei produced multiple dehydrogenases including formate, malate, and lactate oxidase at high levels, along with cytochromes a, b, and c. When grown under low oxygen tension, these oxygen-dependent enzymes showed two to twenty-fold reductions in activity. Conversely, fumarate reductase activity increased four-fold under low oxygen conditions. Notably, cytochrome a was absent in low-oxygen cultures, while cytochrome b remained prominent in membranes and cytochrome c appeared in the soluble fraction. The findings suggest that M. phlei shifts its electron transport strategy under oxygen limitation, likely using fumarate as an alternative electron acceptor instead of oxygen, similar to mechanisms observed in other bacteria. This metabolic flexibility demonstrates how mycobacteria adapt their respiratory systems to environmental changes in oxygen availability.

Key findings

• Aerobically grown M. phlei showed 2-20 fold higher activities of formate dehydrogenase, malate dehydrogenase, lactate oxidase, β-hydroxybutyrate dehydrogenase, and NADH dehydrogenase compared to low oxygen cultures
• Fumarate reductase activity increased approximately four-fold in low oxygen tension cultures, suggesting fumarate becomes the primary electron acceptor under hypoxic conditions
• Cytochrome a was absent from low oxygen cultures while cytochrome b remained in membranes and cytochrome c was present in the soluble fraction, indicating altered electron transport chain composition
• Glucose-6-phosphate dehydrogenase and malate:vitamin K dehydrogenase activities were unaffected by oxygen tension, while lactate dehydrogenase was absent in both culture conditions