Isolation and characterization of Desulfovibrio growing on hydrogen plus sulfate as the sole energy source

Two sulfate reducing bacteria (Madison and Marburg strains) that grew on H₂ plus sulfate in a mineral salts medium that contained acetate and CO₂ as sole carbon source were isolated from diverse environments. During growth in this medium 4.2 mol of H₂ were consumed per mol of sulfate reduced to sulfide. Acetate was required for biosynthetic purposes only. Approximately 70% of the cell carbon synthesized was derived from acetate and 30% from CO₂. Acetate was not involved in dissimilatory sulfate reduction.Growth of the bacteria on H₂ plus sulfate was linear rather than exponential, and a doubling time at the beginning of linear growth of approximately 3 h was observed. The optimal growth temperature was found to be near 35° C. Cultures could be grown up to a density of 500 mg cells (dry weight) per liter. Growth yield studies demonstrated that between 4 and 5 g of cells (dry weight) were formed per mol of sulfate reduced to sulfide.The chemolithotrophically growing sulfate reducing isolates were identified as Desulfovibrio species by being obligately anaerobic, gram negative, non spore forming vibrios that contained desulfoviridin and cytochrome c₃ (350–450 nmol/g protein). The organisms were found to be monopolarly and monotrichously flagellated. The abilities of the two strains to grow on electron donors other than H₂ and to use electron acceptors other than sulfate differed considerably. The DNA base composition of the Madison and Marburg strains were 60 and 63.5 mol % GC, respectively. The taxonomic status of the strains was discussed.     

Significance of hydrogen burst from growing cultures of Desulfovibrio vulgaris,Miyazaki, and the role of hydrogenase and cytochrome c3 in energy production system

In an early stage of the growth of Desulfovibrio vulgaris, Miyazaki, a burst of H₂ occurred, and lasted for a few hours. The H₂S production which paralleled the cell proliferation was very low in the H₂ burst period, and began to increase thereafter. Hydrogenase (hydrogen: ferricytochrome c₃ oxidoreductase, EC1. 12.2.1), cytochrome c₃ and desulfoviridin also increased after the H₂ burst. These phenomena were common to all the cultural conditions tested, i.e., the cell growth is always preceded by the initial H₂ burst. Hydrogenase of cells harvested in the H₂ burst peroid was composed mainly of the high molecular weight species (mol. wt., 180,000), whereas that of the cells harvested later was composed of both the high molecular weight and the low molecular weight (mol. wt., 70,000) species. It was suggested that the former enzyme was acting as a catalyzer in the initial H₂ burst to effect the substrate level phosphorylation during the breakdown of lactate to acetate and CO₂, whereas the latter was induced by the H₂ produced by the cells themselves to recycle H₂ in order to supply electrons to the reducing system of sulfur oxy-acids coupled to electron transfer phosphorylation. The amount of cytochrome c₃ in cells harvested from an iron-deficient medium was as high as that in cells harvested from an iron-rich medium, suggesting the significance of this electron carrier in the cellular metabolism.     

The effect of transfer from low to high light intensity on electron transport in Rhodospirillum rubrum membranes

The effects of transfer from low to high ligh intensity on membrane bound electrontransport reactions of Rhodospirillum rubrum were investigated. The experiments were performed with cultures which did not form bacteriochlorophyll (Bchl) for about two cell mass doublings during the initial phase of adaptation to high light intensity. Lack of Bchl synthesis causes a decrease of Bchl contents of cells and membranes. Also, the cellular amounts of photosynthetically active intracytoplasmic membranes decrease.In crude membrane fractions containing both cytoplasmic and intracytoplasmic membranes the initial activities of NADH oxidizing reactions increase only slightly (about 1.2 times) per protein, but the initial activities of succinate oxidizing reactions decrease (multiplied by a factor of 0.7). On a Bchl basis activities of NADH oxidizing reactions increase 3.4 times while activities of succinate dependent reactions increase 1.9 times. With isolated intracytoplasmic membranes activities of NADH as well as succinate dependent reactions increase to a comparable extent on a Bchl basis (about 1.8 times) and stay nearly constant on a protein basis. Cytochrome c oxidase responds like succinate dependent reactions. The data indicate that in cells growing under the conditions applied NADH oxidizing electron transport systems are incorporated into both, cytoplasmic and intracytoplasmic membranes, while incorporation of succinate oxidizing systems is confined to intracytoplasmic membranes only.Activities of photophosphorylation and succinate dependent NAD⁺ reduction in the light increase per Bchl about 1.8 times. On a Bchl basis increases of the fast light induced on reactions at 422 nm and increases of soluble cytochrome c ₂ levels are comparable to increases of photophosphorylations and succinate dependent activities. But increases of slow light off reactions at 428 nm and of b-type cytochrome levels become three times greater then increases of cytochrome c ₂ reactions and levels. These results infer that although electrontransport reactions of intracytoplasmic membranes change correlated to each other, Bchl, cytochrome c ₂ and b-type cytochromes cellular levels are independent of each other. Furthermore, the data indicate that cytochrome c ₂ rather than b-type cytochrome is involved with steps rate limiting for photophosphorylation.Abbreviations Bchl bacteriochlorophyll - DCIP 2,6-dichlorophenolindophenol