Metabolic function of branched-chain volatile fatty acids, growth factors for ruminococci. II. Biosynthesis of higher branched-chain fatty acids and aldehydes

Cellular fatty acid composition and identification of rumen bacteria

The fatty acid compositions of 21 pure cultures of rumen bacteria, representing 12 genera and 14 species, were compared as methyl esters. Each organism possessed a consistent and reproducible fatty acid profile. Overlapping similarities and differences in composition did not allow differentiation between families or genera. Although species differentiation was possible, fatty acid composition appeared to be only an aid in the identification of bacteria.

The separation and identification of the lipids of Rhodopseudomonas spheroides

Detailed examination of the lipids of Rhodopseudomonas spheroides was undertaken since it was thought this might provide information on the biogenesis of the chromatophores. The phospholipids of purified chromatophores consist of phosphatidylethanolamine (35%), phosphatidylglycerol (34%) and phosphatidylcholine (23%); minor quantities of phosphatidic acid and of cardiolipin were also found. In addition, a sulpholipid was detected and also a new lipid containing ornithine. The relative proportions of the different phospholipids in chromatophores, in other subcellular fractions from pigmented micro-organisms and in fragments from cells grown under oxygen were similar. However, the ‘aerobic fragments’ contained much less ornithine lipid than the chromatophores. Comparison of the relative amounts of the different phospholipids in whole cells grown under oxygen, under air, or under semi-anaerobic conditions in the light showed no marked differences, the composition being similar to that found in chromatophores. It is concluded that there is no particular lipid specifically associated with chromatophores. Poly- β -hydroxybutyrate accounted for as much as 35% of the dry weight of cells grown under oxygen in the dark on malate-glutamate medium. It is necessary to remove this material before chromatography as it otherwise interferes with the separation.

Cultural characteristics and fatty acid composition of Corynebacterium acnes

A detailed study of the cultural characteristics and cellular fatty acid composition of 27 isolates of Corynebacterium acnes was performed to establish the properties by which this organism may be identified and characterized. The fatty acids were extracted directly from whole cells and examined as methyl esters by gas-liquid chromatography. Each strain possessed a similar fatty acid profile which was characterized by a large percentage of C15 branched-chain acid. Uniformity in certain biochemical reactions and cultural characteristics was also observed. All strains were catalase-positive, nonmotile, and urease-negative, reduced nitrate, liquefied gelatin, failed to hydrolyze esculin and starch, and gave a positive methyl red test. Glucose, fructose, and glycerol were fermented, but not lactose, salicin, sucrose, maltose, xylose, or arabinose. Production of hydrogen sulfide and indole, fermentation of mannitol, and hemolytic activity were variable characteristics. Two species of the genus Propionibacterium were also tested and found to be similar to C. acnes both in cultural characteristics and fatty acid composition. The results strengthen previous suggestions that C. acnes should be classified in the genus Propionibacterium.

Volatile fatty acid requirements of cellulolytic rumen bacteria

A gas chromatographic method was developed which could separate the isomers isovaleric and 2-methylbutyric acid. Subsequent analyses revealed that most commercially available samples of these acids were cross-contaminated; however, one sample of each acid was found to be pure by this criterion. The growth response of seven strains of cellulolytic rumen bacteria (three strains of Bacteroides succinogenes, three strains of Ruminococcus flavefaciens, and one strain of R. albus) to additions of isobutyric, isovaleric, 2-methylbutyric, valeric, and combinations of valeric and a branched-chain acid was determined. Strains of B. succinogenes required a combination of valeric plus either isobutyric or 2-methylbutyric acid. Isovaleric acid was completely inactive. Either isobutyric or 2-methylbutyric acid was required for the growth of R. albus 7. Strain C-94 of R. flavefaciens grew slowly in the presence of any one of the three branched-chain acids, but a combination of isobutyric and 2-methylbutyric acids appeared to satisfy this organism's growth requirements. None of the individual acids or mixtures of straight- and branched-chain acids allowed growth of R. flavefaciens strain C1a which would approach the response obtained from the total mixture of acids. Further work indicated that all three branched-chain acids were required for optimal growth by this strain, although isovaleric acid only influenced the rate of maximal growth. Either 2-methylbutyric or isovaleric acid allowed growth of nearly the same magnitude as that of the positive control for R. flavefaciens B34b. The presence of acetic acid had little influence on the rate or extent of growth of any of the strains except R. albus 7, for which the extent of growth was markedly increased. Determination of the quantitative fatty acid requirements for the three B. succinogenes strains indicated that 0.1 mumole of valeric per ml and 0.05 mumole of 2-methylbutyric per ml permitted maximal growth. However, with isobutyric acid as the branched-chain component, strains A3c and B21a required 0.1 mumole/ml in contrast to S-85 which exhibited optimal growth at the 0.05 mumole/ml level. By use of mixtures of isobutyric and 2-methylbutyric acids, good growth of C-94 was obtained at concentrations of 0.1 and 0.01 mumole/ml, respectively. About 0.3 mumole/ml of each acid was required for satisfactory growth of C1a.

Biosynthesis of phenylalanine from phenylacetate by Chromatium and Rhodospirillum rubrum

Cultures of Chromatium strain D and Rhodospirillum rubrum incorporated (14)C from phenylacetate-1-(14)C during anaerobic growth. The radioactivity in the protein fraction of cells was mainly in phenylalanine. Phenylalanine from Chromatium cells grown in phenylacetate-1-(14)C was labeled at carbon 2. Incorporation of phenylacetate by Chromatium was decreased in the presence of exogenous phenylalanine, and de novo synthesis of phenylalanine from bicarbonate was less in medium containing either phenylalanine or phenylacetate. These organisms, and also certain anaerobic rumen bacteria, apparently carboxylate phenylacetate to synthesize the phenylalanine carbon skeleton. The mechanism of the carboxylation is unknown; however, it appears to be dependent upon anaerobic conditions, since R. rubrum did not synthesize phenylalanine from phenylacetate during aerobic growth in the dark.

Importance of the isovalerate carboxylation pathway of leucine biosynthesis in the rumen

Certain anaerobic ruminal bacteria synthesize the leucine carbon skeleton by use of a pathway different from that described in other microorganisms. These organisms carboxylate the intact carbon skeleton of isovalerate, synthesizing leucine-2-C(14) from isovalerate-1-C(14). Strains of Bacteroides ruminicola and Peptostreptococcus elsdenii were like Ruminococcus flavefaciens in that they incorporated appreciable amounts of C(14) from isovalerate-1-C(14) into cellular protein and in that the only labeled amino acid found was leucine. The specific activity of beta-isopropylmalate dehydrogenase in extracts from R. flavefaciens and from the mixed bacterial population from the rumen was very low as compared with the specific activity of this enzyme in extracts from Escherichia coli. This suggests that the pathway of leucine biosynthesis that operates in many aerobic and facultative microorganisms is not the major pathway in rumen bacteria. This was supported by the finding that after fermentation of whole rumen contents with acetate-2-C(14), leucine from the bacterial cells had a specific activity lower than one would expect if acetate was incorporated directly into carbons 1 and 2 of leucine.

Importance of the isovalerate carboxylation pathway of leucine biosynthesis in the rumen

Certain anaerobic ruminal bacteria synthesize the leucine carbon skeleton by use of a pathway different from that described in other microorganisms. These organisms carboxylate the intact carbon skeleton of isovalerate, synthesizing leucine-2-C(14) from isovalerate-1-C(14). Strains of Bacteroides ruminicola and Peptostreptococcus elsdenii were like Ruminococcus flavefaciens in that they incorporated appreciable amounts of C(14) from isovalerate-1-C(14) into cellular protein and in that the only labeled amino acid found was leucine. The specific activity of beta-isopropylmalate dehydrogenase in extracts from R. flavefaciens and from the mixed bacterial population from the rumen was very low as compared with the specific activity of this enzyme in extracts from Escherichia coli. This suggests that the pathway of leucine biosynthesis that operates in many aerobic and facultative microorganisms is not the major pathway in rumen bacteria. This was supported by the finding that after fermentation of whole rumen contents with acetate-2-C(14), leucine from the bacterial cells had a specific activity lower than one would expect if acetate was incorporated directly into carbons 1 and 2 of leucine.

Nutritional requirements of anaerobic spirochetes. I. Demonstration of isobutyrate and bicarbonate as growth factors for a strain of Treponema microdentium

Hardy, Paul H., Jr. (The Johns Hopkins University School of Medicine, Baltimore, Md.), and Carole O. Munro. Nutritional requirements of anaerobic spirochetes. I. Demonstration of isobutyrate and bicarbonate as growth factors for a strain of Treponema microdentium. J. Bacteriol. 91:27-32. 1966.-The previously reported ability of a microaerophilic diphtheroid to support the growth of some oral spirochetes resides in the acid-distillable fraction of the culture fluid. This fraction can be replaced by isobutyrate and, to a lesser extent, by 2-methylbutyrate. When media are supplemented with isobutyrate alone, there is a prolonged lag phase before spirochetal growth commences, but when sodium bicarbonate is also added the lag phase is shortened, and both the growth rate and the total yield are increased. Serum, in low concentration, also acts as a growth stimulant, but it is inhibitory when present at higher concentrations.

STUDIES OF THE LIPIDS OF ARTHROBACTER GLOBIFORMIS 616: I. THE FATTY ACID COMPOSITION

Nearly 96% of the fatty acids of Arthrobacter globiformis 616 cultivated in a glucose – mineral salts – nitrate medium were of the branched-chain type. The fatty acids, identified by melting point and by infrared, mass, and nuclear magnetic resonance spectra were (in order of abundance) 12-methyl tetradecanoic, 14-methyl hexadecanoic, 14-methyl pentadecanoic, hexadecanoic, 12-methyl tridecanoic, and tetradecanoic.