Influence of available aluminium on soil micro-organisms

P. ILLMER, K. MARSCHALL AND F. SCHINNER. 1995. Forest soils were selected which covered a wide range of aluminium concentrations (7 to μmol g^-1dry matter), but which differed as little as possible from one another in their soil chemical characteristics, including pH. These soils were examined with respect to microbial biomass and respiration, activity of cellulase, N-mineralization, colony-forming units of bacteria and fungi, and the concentrations of several inorganic soil components. The influences of altitude, climate, vegetation and, especially, of soil acidity could be kept to a minimum and so differences between the soil microfloras could clearly be attributed to Al concentration.
Al concentration was recognized to be the main inhibiting factor for the microbial biomass in soil. While N-mineralization was severely inhibited by aluminium, cellulase activity was hardly affected by increasing Al concentrations.
By taking the Al concentration along with various other soil chemical parameters a linear model could be developed that allowed more than 98% of the variability of the microbial biomass in soil to be explained.     

Microbial diversity in soil: effect of releasing genetically engineered micro-organisms

This review examines the potential for change in microbial diversity, with the emphasis on bacteria, in soil resulting from the introduction of genetically engineered microorganisms (GEMs). With the advent of GEMs came the impetus for new technologies to recover these micro-organisms from soil and to assess their effects on microbial diversity. This review also presents general aspects of and genetic approaches to accessing bacterial diversity in the environment.     

The use of thin soil sections for the study of soil micro-organisms

Summary Modifications of Alexander and Jackson's¹ technique for the preparation of thin soil sections are described.The distribution of bacterial colonies within soil aggregates has been examined using this technique and it has been demonstrated that distinct distribution patterns may occur.     

The sterilizing effect of ethylene oxide vapor on different micro-organisms

Zusammemfassung Äthylenoxyd-Gas ist ein effektives Sterilisierungsmittel. Konzentration und Sterilisierungszeit sind voneinander abhängig. Je länger die Wirkungszeit, desto geringer die lethale Gaskonzentration. Bezüglich ihrer Widerstandsfähigkeit lassen sich die Mikroorganismen in drei Gruppen einteilen (Abb. 1). Am meisten resistent sind die sporenbildenden Bakterien. Sie vertragen eine zweifach so hohe Konzentration als die nicht sporenbildenden. Auffallend niedrig liegt die tödliche Grenze für Hefe und Schimmelpilze.

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This investigation was supported in part by a research grant [B-633 (C 2)] from the National Institute of Neurological Diseases and Blindness, Public Health Service, and by the Charles Irwin Travelli Fund.     

The effect of benzoyl peroxide on cutaneous micro-organisms in vitro

The survival curves of cutaneous micro-organisms in the presence of benzoyl peroxide were investigated. All the curves exhibited a shoulder prior to exponential cell death. Benzoyl peroxide was lethal to the cutaneous organisms tested and they varied in sensitivity increasing as follows: Propionibacterium acnes, Staphylococcus capitis, Staph. epidermidis, Staph. hominis, Prop, avidum, Prop. granulosum and Pityrosporum ovale.     

Effect of antibiotics on ethylene production by soil micro-organisms

Summary Treatment of arable soils with antibacterial (novobiocin) and antifungal (cycloheximide) agents had no effect on ethylene accumulation. Novobiocin had a very small effect on the growth ofMucor hiemalis and cycloheximide decreased its maximum specific growth rate but neither agent impaired the capacity of the fungal culture to produce ethylene. Caution must therefore be exercised when using antibiotics to establish the source of soil metabolic processes.     

Colonization of cotton roots by soil micro-organisms

An experiment was carried out to study the colonization of soil microorganisms on cotton roots buried in the soil.Fusarium culmorum, F. solani, F. oxysporum, Macrophomina phaseoli andBacillus sp. were found to be the predominant colonizers followed byBotryodiplodia theobromae, Fusarium acuminatum, Aspergillus niger, A. flavus, Stachybotrys atra, Tilachlidium humicola andRhizopus sp. The practice of leaving cotton roots in the soil would therefore add to the building up of the inoculum potential of the soil inhabiting fungi several of which are serious root pathogens.     

The influence of soil micro-organisms on the growth and chemical composition of soybean

Summary A plastic film isolator was adapted for the growth of soybeans in sterile soil, sterile reinoculated soil, and unsterilized soil. The presence of micro-organisms significantly increased the mass of tops and roots as well as the plant content of Ca, Mg, Fe, Al, Cu, Zn, and Mo. Plant content of N, P, and K was not affected by microbial activity, while manganese, made available by steam-sterilization, was oxidized to unavailable forms by the soil microflora. The mixed microflora influenced the quantity and distribution of free amino acids within the plant but did not affect the distribution of amino acids within the crude protein fraction.     

Production of organic acids by soil micro-organisms

Summary Micro-organisms of the rhizosphere soils in respect of four plant speciesviz sesbania, cowpea, sorghum, and finger millet and those of the non-rhizosphere soil (control) maintained under pot culture conditions were incubated for a fortnight in liquid media containing glucose and the relative amounts and nature of the organic acids produced were investigated by pH changes and chromatographic studies respectively. Micro-organisms with the rhizosphere of all the four plant species produced greater amounts of acids than those of the non-rhizosphere soil. Rhizosphere micro-organisms with legumes produced greater amounts of acids than those with non-legumes. However no qualitative differences were observed in the organic acids produced by the rhizosphere micro-organisms of the four plant species investigated as well as those of non-rhizosphere soil.     

Aspects of antagonisms between micro-organisms in soil

Summary Attention is called to certain aspects of microbial antagonisms in soil. Tests on the interaction of 90 strains of actinomycetes, isolated by non-selective procedure from the rhizosphere of potatoes grown in scab-infected soil which had been favorably modified by organic amendment, showed that within a group of 11 strains, found to be antagonistic toStreptomyces scabies, a wide range of cross-antagonisms existed. The possible importance of this in the study of specific antagonist-pathogen relationships is indicated, as well as that of the 'rhizosphere effect' in modifying the microbiological equilibrium in soil.Contribution No. 272 (Journal Series) from the Division of Bacteriology and Dairy Research, Science Service, Department of Agriculture, Ottawa, Canada.     

The effect of humic substances on the respiration and growth of micro-organisms

Summary The main effects exerted by humic substances on plant and microbial metabolism are outlined. The effect of various humic fractions obtained from peat are examined using a yeast,Candida utilis as a test organism. Humic fractions exerted no effect on respiration or growth of the micro-organism. Various postulates are put forward to account for this no effect response.     

Molecular and functional diversity in soil micro-organisms

Traditional approaches to the study of microbial diversity have relied on laboratory cultivation of isolates from natural environments and identification by classical techniques, including analysis of morphology, physiological characteristics and biochemical properties. These approaches provide information on fine-scale diversity but suffer from bias, resulting from the media and cultivation conditions employed, and from the inability to grow and isolate significant proportions of natural communities in the laboratory. An alternative approach is the amplification of ribosomal RNA and functional genes from nucleic acids extracted directly from environmental samples, with subsequent analysis by `fingerprinting' methods or by sequencing and phylogenetic analysis. This approach avoids the need for laboratory cultivation and has provided major insights into species and functional diversity of bacterial and archaeal populations. This article reviews molecular approaches to the characterisation of prokaryote diversity in natural environments, their more recent application to fungal diversity and the advantages and limitations of molecular analyses.     

Quantitative structure—activity relationship study on the inhibitory effect of some herbicides on the growth of soil micro-organisms

The effect of eight herbicides on the growth of six soil bacteria and three microscopic fungi, and on the amylase, cellulase and dehydrogenase activity in a Hungarian soil was determined. Herbicide decomposition rate in the soil was also assessed. Qualitative structure-activity relationship (principal component analysis, spectral mapping technique and stepwise regression) analysis showed that the overwhelming majority (about 80%) of the effect of herbicides can be explained by one background variable showing the similarity between their mode of action. The two-dimensional non-linear map of principal component loadings and spectral map characteristics suggested that the number of substituents may be important in the determination of the toxic effects. The inhibition of bacterial growth, inhibition of fungal growth, and effects on enzyme activity and decomposition rate all formed different clusters on the maps indicating that herbicides influence these processes differently. Of the nine physicochemical parameters considered, only the electron withdrawing capacity of substituents significantly influenced the biological activity of herbicides, suggesting that electrostatic interactions between the herbicide molecules and micro-organisms is important.     

Effect of copper on the degradation of phenanthrene by soil micro-organisms

AIMS: The effect of copper on the degradation by soil micro-organisms of phenanthrene, a polycyclic aromatic hydrocarbon, was investigated. METHODS AND RESULTS: Inert nylon filters were incubated in the soil for 28 days at 25 degrees C. Each filter was inoculated with a soil suspension, phenanthrene (400 ppm), copper (0, 70, 700 or 7000 ppm) and nitrogen/phosphorus sources. The filters were assessed for phenanthrene degradation, microbial respiration and colonization. Phenanthrene degradation proceeded even at toxic copper levels (700/7000 ppm), indicating the presence of phenanthrene-degrading, copper-resistant and/or -tolerant microbes. However, copper at these high levels reduced microbial activity (CO2 evolution). CONCLUSION: High levels of copper caused an incomplete mineralization of phenanthrene and possible accumulation of its metabolites. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of heavy metals in soils could seriously affect the bioremediation of PAH-polluted environments.