Dimethylsulfoxide respiration in Proteus mirabilis and Escherichia coli
It has been found that Ersteus mirabilis and Escherichia gali can use dimethylsulfoxide (DMSO) as an electron acceptor for anaerobic growth. During growth, DMSO was reduced to dimethylsulfide (DMS) as determined by gas chromatography. During a survey of carbon sources capable of supporting DMSO dependent respiration in E.* mirabilis. it was found that fermentable substrates such as glucose and pyruvate as well as oxidizable substrates such as glycerol and lactate are capable of supporting DMSO respiration. In addition, in a complex medium formate greatly stimulates growth in the presence of DMSO. When cell extracts were assayed for DMSO reduction, it was found that NADH, reduced methyl viologen, reduced benzyl viologen, formate, and lactate can serve as electron donors, whereas NADPH is a very poor donor. Chlorate resistant mutants were isolated and were found to be unable to use DMSO as an electron acceptor. These mutants can be divided into at least two groups. In the first group, growth and DMSO reduction can be restored by a high concentration of molybdate in the medium, whereas in the second group, growth and DMSO reduction cannot be restored. DMSO supports anaerobic growth of £. coli on glycerol and slightly enhances growth on glucose. When cell extracts were assayed for DMSO reduction it was found that NADH, formate, lactate, reduced methyl viologen, and reduced benzyl viologen can serve as electron donors while NADPH is a very poor donor. When chlorate resistant mutants (chi) of E.coli. chlA. chlB. chlD. and chlE were tested, they were unable to grow using DMSO as an electron acceptor. However, in the case of the chlD mutant, growth and DMSO reduction could be restored by a high concentration of molybdate. Thus it appears that molybdenum cofactor is involved in DMSO reduction. Similarly, mutants of E.coli blocked in menaquinone (vitamin-Kg) biosynthesis (men), menB and menC were tested and were unable to grow utilizing DMSO as an electron acceptor. Growth and DMSO reduction can be restored to these mutants by the addition of either &-succinylbenzoic acid or 1,4-dihydroxy-2- napthoic acid depending on the metabolic block of the mutants. These results establish that menaquinone is involved in DMSO reduction. A comparison of the DMSO reductase activity of E.coli and £. mirahills under various growth conditions has led to the conclusion that Proteus is significantly more efficient than E.coli at gaining energy for growth from the reduction of DMSO.