The Tricarboxylic Acid Cycle in Thiobacillus denitrificans and Thiobacillus-A2

Abstract

S U M M A R YThe enzymes involved in the tricarboxylic acid cycle and some other related reactions were measured quantitatively in cell-free extracts from the obligate autotroph Thiobacillus denitrijicans grown anaerobically, and in the facultative autotroph Thiobacillus-A2 grown under various conditions. The presence of an incomplete tricarboxylic acid cycle in T. denitrijicans and in Thiobacillus-A 2 (when grown autotrophically on thiosulphate) is described. The cell-free extracts from these two organisms lacked a-ketoglutarate dehydrogenase and succinyl CoA synthetase. The data from Thiobacillus-A z grown on succinate, aerobically or anaerobically, and on glutamate aerobically suggest that both the enzymes are repressed during autotrophic growth. Results are further discussed in relation to possible reasons for autotrophy.

A proteomic view of the facultatively chemolithoautotrophic lifestyle of Ralstonia eutropha H16

“…This is achieved by repressing the expression of α‐ketoglutarate dehydrogenase. A representative of this group of organisms is P. versutus A2 54, 56. Unlike P. versutus A2, R. eutropha H16 maintains a functional TCA cycle during lithoautotrophic growth.…”

CC Bond-Forming Reactions of IrIII-Alkenyls and Nitriles or Aldehydes: Generation of Reactive Hydride- and Alkyl-Alkylidene Compounds and Observation of a Reversible 1,2-H Shift in Stable Hydride–IrIII Alkylidene Complexes

“…These organisms usually lack a functional α‐ketoglutarate dehydrogenase 14, 15, 55. This type of adaptation has been documented for Thiobacillus denitrificans , Acidithiobacillus ferrooxidans , Hydrogenobacter thermophilus TK‐6, and Nitrosomonas europaea 56–59. Facultative lithoautotrophs, on the other hand, are able to stop the TCA cycle during the phases of lithoautotrophic growth.…”

Autotrophic Metabolism of Formate by Thiobacillus Strain A2

“…During autotrophic growth on either formate or thiosulphate, the much heavier labelling by [14C]acetate of glutamate, proline, arginine and leucine relative to aspartate than with acetate-grown organisms (Table 8) indicated a biosynthetic role for the tricarboxylic acid cycle predominantly for the conversion of acetate to glutamate via 2-oxoglutarate7 as occurs exclusively in obligate chemolithotrophs (Smith et al, 1967;Kelly, 1971). The reported absence of 2-oxoglutarate dehydrogenase from autotrophic Thiobacillus A2 (Peeters et al, 1970) suggests that the observed labelling of aspartate-family amino acids was due to a functional glyoxylate bypass, the enzymes for which are present in autotrophic Thiobacillus A2 (Peeters et al, 1970). These experiments and others (Whittenbury & Kelly, 1977) demonstrate the strong regulatory control exhibited by Thiobacillus A2 over the selection of pathways for intermediary metabolism dependent on the growth substrate conditions.…”