Aerobic growth brings with it the metabolic byproducts of oxygen mediated reactions. Chief culprit is reactive oxygen species (ROS) that can induce an oxidative stress response. Research has suggested that glyoxylate cycle in many bacteria could help ameliorate oxidative stress in cells, and help provide a conducive environment for aerobic respiration. This suggests that glyoxylate cycle is needed for aerobic bacterial species. However, my personal experience with Bacillus subtilis suggests a rethink for the above postulation.
Specifically, glyoxylate cycle is in essence a short circuit tricarboxylic acid cycle where isocitrate lyase breaks down isocitrate into glyoxylate and succinate. Glyoxylate subsequently condense with acetyl-CoA through the action of malate synthase to form malate that moves to form oxaloacetate and citrate to complete the glyoxylate cycle. Thus, only two additional enzymes, isocitrate lyase and malate synthase are required to deliver glyoxylate cycle. These two enzymes are not present in B. subtilis 168. However, experimental tests have revealed that the bacterium could grow well in LB medium at 30 and 37 oC under aerobic conditions. The results thus suggest that glyoxylate cycle is not strictly essential for ameliorating oxidative stress that arises from aerobic respiration. Collectively, the finding adds another dimension into the intellectual discourse on the functionality, evolutionary premise, and essentiality of glyoxylate cycle in aerobic microorganisms which may open up new frontiers for our understanding of cellular metabolism in general, and tricarboxylic acid cycle in particular.
Category: biochemistry, biotechnology, cell biology, microbiology,
Tags: glyoxylate cycle, tricarboxylic acid cycle, Bacillus subtilis, malate synthase, isocitrate lyase,
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