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Biomedical subjects

M Alexander

Publications and source records attributed to M Alexander.

At least 397 records · Page 22Linked to original sources
PubMed1971

Effect of chemical structure on the biodegradability of aliphatic acids and alcohols.

Sewage microorganisms readily degraded unsubstituted aliphatic acids, but the rate of decomposition was much slower with substituted acids as substrates. The type, number, and position of the substituents governed the rate of the oxidation. A single halogen, particularly if on the alpha-carbon, decreased the rate of biodegradation, but the dihalogenated compounds tested were especially resistant. Dimethyl-substituted aliphatic acids and alcohols were also poorly utilized. Bacteria unable to grow on certain brominated fatty acids were capable of oxidizing and dehalogenating omega- but not alpha-bromoaliphatic acids.

Alcohols↗
PubMed1971

Formation of nitrate from 3-nitropropionate by Aspergillus flavus.

Extracts of the hyphae of a nitrifying strain of Aspergillus flavus formed nitrite and nitrate from 3-nitropropionate. Nicotinamide adenine dinucleotide phosphate and nicotinamide adenine dinucleotide enhanced the production of nitrate but not nitrite, whereas cysteine and diethyldithiocarbamate increased nitrite but diminished nitrate synthesis. Quinacrine reduced the extent of conversion of the nitro compound to nitrite and nitrate, but only the inhibition of nitrite formation was completely reversed by flavine coenzymes. Molecular oxygen was essential for this part of the nitrification sequence. 3-Chloropropionate stimulated the oxidation of nitrite by hyphae or enzyme preparations. Although the fungus contained a noncytochrome-linked nitrite-oxidizing enzyme, partially purified preparations free of this enzyme formed both nitrite and nitrate from 3-nitropropionate. Possible mechanisms of this latter stage of heterotrophic nitrification are discussed.

Aspergillus↗
PubMed1971

Formation of tumor-like structures on legume roots by Rhizobium.

Tumor-like structures appeared on the roots of Medicago sativa, Alysicarpus vaginalis, and Trifolium pratense inoculated with a non-nodulating strain of Rhizobium trifolii or with irradiated cultures of either of two nodulating Rhizobium strains. The structures were composed of disorganized plant tissues which, on the basis of microscopic examination, were devoid of bacterial cells. Rhizobia which could nodulate legumes of one cross-inoculation group and which were able to induce formation of such tumor-like structures on plants of a second cross-inoculation group were isolated from extracts of these root growths. The apparent tumorogenic activity of some of the rhizobia, but not their nodulating capacity, was lost when the bacteria were transferred in laboratory media.

Agglutination Tests↗
PubMed1971

Resistance of Zygorhynchus species to lysis.

Zygorhynchus vuilleminii, a nonmelanin-containing fungus, was not lysed by mycolytic actinomycetes. Several enzymes and Streptomyces enzyme preparations digesting walls of other fungi were without appreciable activity on walls of Zygorhynchus species. A bacterium able to solubilize a portion of the Zygorhynchus wall released little or no reducing sugars from these structures. Fractions of Z. vuilleminii walls were resistant to glucanase hydrolysis, but certain fractions were digested by chitinase and microbial enzyme preparations. The walls and several wall fractions were not readily susceptible to degradation by a soil community. Walls of lysis-resistant Zygorhynchus species contained glucosamine, fucose, glucuronic acid, and galactose but little or no glucose. Resistant wall fractions were rich in uronic acid and fucose, whereas the readily degradable fractions contained abundant glucosamine. Cultural conditions affected the extent of digestion and composition of the walls. Possible reasons for the resistance of Zygorhynchus to lysis in nature are discussed.

Carbohydrates↗
PubMed1970

DDT metabolites and analogs: ring fission by Hydrogenomonas.

A Hydrogenomonas cleaved one of the rings of p,p'-dichlorodiphenylmethane, a product of DDT metabolism, to yield p-chlorophenylacetate and further metabolized the latter compound. Products of microbial degradation of other diphenylmethanes were also identified. Substituents on the methylene-carbon and para-chloro substitution are critical factors governing resistance of DDT and related compounds to aerobic metabolism and decomposition by the bacterium.

Benzophenones↗
PubMed1970

Cometabolism of m-chlorobenzoate by an Arthrobacter.

Twenty isolates representing nine bacterial genera were obtained from enrichment cultures and were shown to cometabolize one or more of 22 substituted benzoates. One of the isolates, an Arthrobacter sp., cometabolized m-chlorobenzoate to a product identified as 4-chlorocatechol by thin-layer chromatography and ultraviolet and infrared spectroscopy. The data indicate that cometabolism by the arthrobacter results from the formation of products by its benzoate-oxiding enzyme system that are not acted upon by the catechol-metabolizing enzymes of the bacterium.

Amines↗
PubMed1970

Bacterial degradation of diphenylmethane, a DDT model substrate.

A strain of Hydrogenomonas was isolated by elective culture in a solution with diphenylmethane, an analogue of DDT, as the sole carbon source. Constitutive enzymes effected the oxidation and fission of one of the benzene rings of diphenylmethane, and phenylacetic acid was found as a major degradation product. Small amounts of phenylglyoxylic and benzoic acids were also generated from diphenylmethane by the bacterium. Phenylacetic acid, which contains the second benzene ring of diphenylmethane, was metabolized by inducible enzymes.

Benzene Derivatives↗