Requirement of heme for growth of Bacteroides fragilis.

Heme or protoporphyrin IX was required for growth of Bacteroides fragilis in a defined medium. The amount of heme necessary for half-maximal growth was 2 to 10 ng/ml (3.8 to 15 pmol/ml) among the Bacteroides species and strains tested. The growth rate, metabolic products from glucose fermentation, and cell yields were affected by the concentration of heme in the medium and by the length of time the culture was incubated. When heme was growth limiting (4 ng/ml), growth rates decreased by 50%, cultures started producing lactic and fumaric acids, and the cell yields declined. The cell yield for B. fragilis (ATCC 25285) at 24 h in medium containing 6.5 microgram of heme per ml was 69 g (dry weight) of cells per mol of glucose compared to 16 g (dry weight) of cells per mol of glucose with 4 ng of heme per ml. B. fragilis was unable to grow in defined medium when a porphyrin precursor, delta-aminolevulenic acid or porphobilinogen, was added in place of heme.

Degradation of homogentisate by strains of Bacillus and Moraxella.

The metabolic pathways whereby strains of Moraxella and Bacillus degrade homogentisate (2,5-dihydroxyphenylacetate) are delineated. The Moraxella (strain OA3) is shown to degrade homogentisate via the pathway previously described in liver: homogentisate is cleaved by a 1,2-dioxygenase (E.C 1.13.11.5) yielding maleylacetoacetate which is isomerized by a GSH-dependent isomerase to fumarylacetoacetate before hydrolysis to acetoacetate and fumarate. A strain of Bacillus (B11c) is shown to catabolize homogentisate via a previously undescribed version of the above sequence: homogentisate is cleaved by a 1,2-dioxygenase (E.C 1.13.11.5) yielding maleylacetoacetate which is hydrolyzed directly to acetoacetate and maleate.

Evidence for cytochrome involvement in fumarate reduction and adenosine 5'-triphosphate synthesis by Bacteroides fragilis grown in the presence of hemin.

Growth of Bacteroides fragilis subsp. fragilis on glucose was very much stimulated by the addition of hemin (2 mg/liter) to the medium. The generation time decreased from 8 to 2 h, and the molar growth yield increased from YM = 17.9 to YM = 47 g (dry weight) of cells per mol of glucose. In the absence of hemin, glucose was fermented to fumarate, lactate, and acetate. The cells did not contain detectable amounts of cytochromes or fumarate reductase. In the presence of hemin, the major products of fermentation were succinate, propionate, and acetate. A b-type cytochrome, possibly a c-type cytochrome, and a very active fumarate reductase were present in the cells. It is concluded from these results that hemin is required by B. fragilis to synthesize a functional fumarate reductase and that the hemin-dependent, enormous increase of the growth yield may be due to adenosine 5'-triphosphate production during reduction of fumarate to succinate.

Regulation of aconitase synthesis in Bacillus subtilis: induction, feedback repression, and catabolite repression.

The synthesis of aconitase in Bacillus subtilis wild-type and different citric acid cycle mutants has been studied and the influence of various growth conditions examined. Aconitase is induced by citrate and precursors of citrate and repressed by glutamate. Induction and repression counteract each other, and at equimolar concentrations of citrate and glutamate, aconitase synthesis is unaffected. Induction by citrate can partly overcome catabolite repression of aconitase. Isocitrate dehydrogenase show endogenous induction of aconitase due to citrate accumulation. Leaky mutants defective in citrate synthase and aconitase cannot be induced by citrate, which indicates that they carry a regulatory mutation. The complex regulation of aconitase is discussed with reference to the participation of this enzyme in glutamate biosynthesis and energy metabolism.