Requirements for Efficient Thiosulfate Oxidation in Bradyrhizobium diazoefficiens
RIKEN Center for Sustainable Resource Science, Yokohama 230-0045, Japan
ETH Zurich, Institute of Microbiology, Vladimir-Prelog-Weg 4, CH-8093 Zurich, Switzerland
Author to whom correspondence should be addressed.
Genes 2017, 8(12), 390; https://doi.org/10.3390/genes8120390
Received: 8 November 2017 / Revised: 7 December 2017 / Accepted: 12 December 2017 / Published: 15 December 2017
(This article belongs to the Special Issue Genetics and Genomics of the Rhizobium-Legume Symbiosis)
One of the many disparate lifestyles of Bradyrhizobium diazoefficiens is chemolithotrophic growth with thiosulfate as an electron donor for respiration. The employed carbon source may be CO2 (autotrophy) or an organic compound such as succinate (mixotrophy). Here, we discovered three new facets of this capacity: (i) When thiosulfate and succinate were consumed concomitantly in conditions of mixotrophy, even a high molar excess of succinate did not exert efficient catabolite repression over the use of thiosulfate. (ii) Using appropriate cytochrome mutants, we found that electrons derived from thiosulfate during chemolithoautotrophic growth are preferentially channeled via cytochrome c550 to the aa3-type heme-copper cytochrome oxidase. (iii) Three genetic regulators were identified to act at least partially in the expression control of genes for chemolithoautotrophic thiosulfate oxidation: RegR and CbbR as activators, and SoxR as a repressor.