Biomedical subjects
Publications and source records attributed to M Alexander.
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Two methods were developed for the assay of substances stimulatory to the nodulation of bean (Phaseolus vulgaris) roots growing from segments of hypocotyl tissue. Coconut water was the chief source of active material, but extracts of cotyledons, hypocotyls and leaves of beans and of horse chestnut fruits were also stimulatory. High concentrations of nitrate improved nodulation both in the presence and absence of coconut water. The ash of coconut water was inactive. Whole alfalfa seedlings formed nodules in the dark when grown in the split medium, but nodulation was not improved by the addition of coconut water.
The nodulation of adventitious roots growing from segments of bean hypocotyl tissue was used as a bioassay for the material present in coconut water which stimulated nodulation. The active material in coconut water is acidic, but it was not possible to extract it from an acid solution with organic solvents. A purification of approximately 70-fold (on a dry wt basis) was obtained using activated charcoal, but at least 10 different compounds were present in the active fractions. A purified fraction of coconut water, which is stimulatory to the growth of carrot root explants, was active in the nodulation assay at a concentration of 2 mug/ml. This represents a 4000-fold purification of the diffusible fraction of coconut water. The charcoal fractionation procedure can be applied to the active material present in extracts of bean leaves.
A microorganism capable of degrading 4-chloro-2-methylphenoxyacetic acid (MCPA) was isolated from soil and identified as Flavobacterium peregrinum. All of the chlorine of MCPA was released as chloride, and the carboxyl-carbon was converted to volatile products by growing cultures of the bacterium, but a phenol accumulated in the medium. The phenol was identified as 4-chloro-2-methylphenol on the basis of its gas chromatographic and infrared characteristics. Extracts of cells of F. peregrinum and of a phenoxyacetate-metabolizing Arthrobacter sp. dehalogenated MCPA and several catechols but not 4-chloro-2-methylanisole. The Arthrobacter sp. cell extract was fractionated, and an enzyme preparation was obtained which catalyzed the conversion of MCPA to 4-chloro-2-methylphenol. The latter compound was not metabolized unless reduced nicotinamide adenine dinucleotide phosphate was added to the fractionated extract. The phenol in turn was apparently oxidized to a catechol by components of the enzyme preparation.
Hyphal walls of Aspergillus phoenicis and Sclerotium rolfsii are composed of large amounts of glucose- and N-acetylhexosamine-containing polysaccharides, and the walls are extensively digested by streptomycete culture filtrates or by a mixture of purified chitinase and beta-(1 --> 3) glucanase preparations with the release of the monomeric units. A. phoenicis conidial walls also contain polymers of glucose and N-acetylhexosamine, but these walls are resistant to digestion by microorganisms or the enzyme combination active on the hyphae. When the melanin-containing spicules were removed from the spore surface, however, the chitinase and glucanase partially digested the underlying structural components. Microorganisms decomposing hyphal walls of S. rolfsii did not attack the melanin-covered sclerotia produced by this fungus. No microorganism capable of lysing two fungi, Rhizoctonia solani and Cladosporium sp., producing hyphae containing abundant melanin was found. The ecological significance of these findings and possible mechanisms for the protective influence associated with melanins are discussed.
Evidence is presented that the resistance of Aspergillus nidulans hyphae to lysis by a beta-(1-->3) glucanase-chitinase mixture results from the presence of melanin in the fungal walls. The resistance of the walls to digestion was directly correlated with the melanin content of the mycelium. A melanin-less mutant of A. nidulans was highly susceptible to hydrolysis by the enzyme mixture. Preincubation of a synthetic melanin with the glucanase, chitinase, and a protease, before addition of the substrate, resulted in a marked inhibition of the rate of substrate hydrolysis. Melanin also appeared to combine with and protect at least certain substrates from decomposition, as indicated by the direct relationship between the extent of inhibition of casein hydrolysis by a bacterial protease and the length of time the protein was incubated with the melanin prior to addition of the enzyme. Melanin was found to be highly resistant to microbial degradation, a likely requirement for the polyaromatic to be effective in protecting fungal structures from lysis or decomposition by natural communities of microorganisms.
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Ether extracts of cultures of 29 strains representing 6 species of Bacillus, and of individual strains of Escherichia coli, Aerobacter aerogenes, and Pseudomonas aeruginosa were examined in a gas chromatograph by use of flame ionization and electron capture detectors. Among the products detected were compounds with the chromatographic characteristics of acetic, propionic, and butyric acids, ethyl alcohol, diacetyl, acetoin, and 2,3-butanediol. The differences in peak areas of the various products formed by the bacteria were determined statistically for the chromatograms obtained with the two detectors, and the peaks were arranged in order of decreasing areas to yield a signature for each bacterial strain. Different signatures were obtained for the various genera and species and for strains of the same species. B. licheniformis, B. subtilis, and A. aerogenes formed significant quantities of a number of volatile compounds, and qualitative and quantitative differences between strains were noted. The electron capture detector was particularly sensitive to diacetyl and acetoin as well as to unknown compounds. By use of this detector, the presence of 5 pg of diacetyl and 20 pg of acetoin could be demonstrated. The quantity of acetoin detected in B. subtilis and B. licheniformis cultures was present in as little as 6.3 x 10(-3) muliters of medium.
Doxtader, K. G. (Cornell University, Ithaca, N.Y.), and M. Alexander. Role of 3-nitropropanoic acid in nitrate formation by Aspergillus flavus. J. Bacteriol. 91:1186-1191. 1966.-Aspergillus flavus formed nitrate, 3-nitropropanoic acid (3-NPA), kojic acid, and a substance tentatively identified as N-formyl-N-hydroxy-glycine during growth in a medium with ammonium as sole nitrogen source. The concentration of the nitro compound reached a maximum prior to the appearance of nitrate; the 3-NPA level subsequently decreased with a concomitant increase in nitrate concentration. Replacement cultures of A. flavus produced nitrate from culture filtrates containing 3-NPA or from synthetic 3-NPA but not when supplied with fresh ammonium-sucrose medium, the nitrate-nitrogen formed being equivalent to 50% of the quantity of the 3-NPA-nitrogen initially present. Neither nitrate nor 3-NPA was synthesized by the fungus during growth in media with low pH or low ammonium concentrations. It is proposed that 3-NPA is either an intermediate or is in equilibrium with an intermediate in nitrification by the fungus.