Acetate metabolisme in Thiobacillus versutus
1987
Claassen, P.A.M.
Thiobacillusversutus was chosen as a modelorganism to study the metabolism of acetate in isocitrate lyase negative organisms.The potential operation of the tricarboxylic acid cycle was established after investigation of the oxidation of acetate by chemolithoautotrophically and heterotrophically grown cells and by measuring the enzyme activities involved in this oxidative cycle. Isocitrate lyase activity, the first enzyme of the glyoxylate cycle, was never observed in calls grown under aerobic conditions whereas malate synthase, catalyzing the second step in this assimilative cycle, was always highest in acetate-grown cells.However, when T.versutus was grown on acetate under denitrifying conditions, isocitrate lyase activity was induced after a certain lag phase during which denitrifying growth took place without the presence of this enzyme. This isocitrate lyase activity was directly linked to the metabolism of acetate during denitrification. Following transition to aerobic growth on this substrate, the activity was actively repressed.Malate synthase activity during denitrifying growth was again highest in acetate-grown cells and the amount was independent of the terminal electron acceptor present, indicating a physiological role of glyoxylate during denitrifying as well as during aerobic growth.The authenticity of the observed isocitrate lyase activity was investigated and appeared to be comparable to isocitrate lyases from other organisms.Although it was found during this study that T.versutus possesses the capacity to synthesize an authentic isocitrate lyase, the reason why this is linked to denitrifying growth and the way acetate is assimilated during aerobic growth remain to be solved.
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