Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany.
Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany.
Biochim Biophys Acta Bioenerg. 2023 Jan 1;1864(1):148932. doi: 10.1016/j.bbabio.2022.148932. Epub 2022 Oct 30.
Many obligately heterotrophic methylotrophs oxidize thiosulfate as an additional electron source during growth on C compounds. Although two different pathways of thiosulfate oxidation are implemented in Hyphomicrobium denitrificans X, a pronounced negative effect on growth rate is observed when it is cultured in the simultaneous presence of methanol and thiosulfate. In this model organism, periplasmic thiosulfate dehydrogenase TsdA catalyzes formation of the dead-end product tetrathionate. By reverse genetics we verified the second pathway that also starts in the periplasm where SoxXA catalyzes the oxidative fusion of thiosulfate to SoxYZ, from which sulfate is released by SoxB. Sulfane sulfur is then further oxidized in the cytoplasm by the sulfur-oxidizing heterodisulfide reductase-like system (sHdr) which is produced constitutively in a strain lacking the transcriptional repressor sHdrR. When exposed to thiosulfate, the ΔshdrR strain exhibited a strongly reduced growth rate even without thiosulfate in the pre-cultures. When grown on methanol, cells exhibit significantly increased NAD/NADH ratios in the presence of thiosulfate. In contrast, thiosulfate did not exert any negative effect on growth rate or increase NAD levels during growth on formate. On both C substrates, excretion of up to 0.5 mM sulfite as an intermediate of thiosulfate (2 mM) oxidation was recorded. Sulfite is known to form adducts with pyrroloquinoline quinone, the cofactor of periplasmic methanol dehydrogenase. We rationalize that this causes specific inhibition of methanol degradation in the presence of thiosulfate while formate metabolism in the cytoplasm remains unaffected.
许多严格需氧的甲基营养菌在以 C 化合物为生长基质时会氧化硫代硫酸盐作为额外的电子供体。尽管在 Hyphomicrobium denitrificans X 中有两种不同的硫代硫酸盐氧化途径，但当同时存在甲醇和硫代硫酸盐时，其生长速率会受到明显的抑制。在这个模式生物中，周质硫代硫酸盐脱氢酶 TsdA 催化形成末端产物连四硫酸盐。通过反向遗传学，我们验证了第二种途径，该途径也起始于周质，其中 SoxXA 催化硫代硫酸盐与 SoxYZ 的氧化融合，然后由 SoxB 释放硫酸盐。然后，硫烷硫通过硫氧化异二硫化物还原酶样系统 (sHdr) 在细胞质中进一步氧化，该系统在缺乏转录抑制剂 sHdrR 的菌株中持续产生。当暴露于硫代硫酸盐时，ΔshdrR 菌株即使在预培养物中没有硫代硫酸盐时，生长速率也会明显降低。当在甲醇上生长时，细胞在存在硫代硫酸盐的情况下表现出显著增加的 NAD/NADH 比值。相比之下，在甲酸盐上生长时，硫代硫酸盐对生长速率没有任何负面影响，也不会增加 NAD 水平。在两种 C 底物上，都记录到高达 0.5 mM 的亚硫酸盐作为硫代硫酸盐（2 mM）氧化的中间产物排出。亚硫酸盐已知会与吡咯喹啉醌形成加合物，吡咯喹啉醌是周质甲醇脱氢酶的辅因子。我们推断，这会导致在存在硫代硫酸盐的情况下，甲醇降解受到特异性抑制，而细胞质中的甲酸盐代谢不受影响。
