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At least 73 records · Page 4Linked to original sources
PubMed1978

Interaction of atrazine with soil microorganisms: population changes and accumulation.

A loam soil treated with atrazine at rates of 10, 30, and 100 microgram/g soil resulted in increased populations of actinomycetes, bacteria, and fungi over those in non-treated soil. The increases were in proportion to the amount of atrazine and persisted for at least 2 months. Living actinomycete amd fungal mycelia were incubated for 48 h in distilled water, nutrient broth, or soil containing 5 microgram/ml (g) of the herbicide. Actinomycete and fungal mycelia accumulated atrazine from water to concentrations up to 87-fold and 132-fold, respectively, over that in the ambient medium. The maximum accumulation from soil by actinomycete mycelia was 26-fold and by fungal mycelia 13-fold. Fungi accumulated little or no atrazine from a nutrient medium whereas actinomycetes accumulated up to 13-fold. Dead mycelia usually did not accumulate atrazine in excess of the ambient concentration. Mycelium of Sclerotium rolfsii growing in a nutrient medium containing 20 microgram atrazine/ml accumulated 157 microgram/g wet weight after 8 days. Sclerotia subsequently produced after transfer of similar mats to soil contained 550 microgram/g wet weight.

Actinomycetales↗
PubMed2001

Antibiotic resistance with particular reference to soil microorganisms.

Evidence of increasing resistance to antibiotics in soil and other natural isolates highlights the importance of horizontal transfer of resistance genes in facilitating gene flux in bacteria. Horizontal gene transfer in bacteria is favored by the presence of mobile genetic elements and by the organization of bacterial genomes into operons allowing for the cooperative transfer of genes with related functions. The selective pressure for the spread of resistance genes correlates strongly with the clinical and agricultural overuse of antibiotics. The future of antimicrobial chemotherapy may lie in developing new antimicrobials using information from comparative functional microbial genomics to find genetic targets for antimicrobials and also to understand gene expression enabling selective targeting of genes with expression that correlates with the infectious process.

Anti-Bacterial Agents↗
PubMed1976

Effect of dicumarol on the growth of some soil microorganisms.

The effect of dicumarol on growth of selected soil bacteria: Azotobacter chroococcum, Arthrobacter globiformis, A. citreus and Bacillus megaterium was studied. The following minimum concentrations were inhibitory in vitro: Arthrobacter citreus--20 mug/ml., Bacillus megaterium--40 mug/ml., Azotobacter chroococcum--40 mug/ml. Arthrobacter globiformis--70 mug/ml. Cells of all microorganisms studied grown in the presence of dicumarol developed aberrant morphological forms.

Arthrobacter↗
PubMed1991

Effect of the fungicides tridemorph and vinclozolin on soil microorganisms and nitrogen metabolism.

The effects of tridemorph and vinclozolin were studied on different types of microorganisms, urea hydrolysis and nitrification in soil and in culture. The fungicides adversely affected the population of bacteria, fungi and actinomycetes as a function of time of incubation. Urea hydrolysis both in culture and soil were also inhibited by the fungicides, and tridemorph was more detrimental. In soil, 45 micrograms/g of tridemorph inhibited 50% of ammonification of urea, ID50 for nitrite production was 750 micrograms/g. In urea-hydrolyzing cultures, 80, 75 and 77 mg/L of tridemorph were the ID50 values for urea hydrolysis by Micrococcus sp., Proteus sp. and P. vulgaris respectively.

Actinomycetales↗
PubMed2005

Stable isotope probing analysis of the influence of liming on root exudate utilization by soil microorganisms.

Rhizosphere microorganisms play an important role in soil carbon flow, through turnover of root exudates, but there is little information on which organisms are actively involved or on the influence of environmental conditions on active communities. In this study, a 13CO2 pulse labelling field experiment was performed in an upland grassland soil, followed by RNA-stable isotope probing (SIP) analysis, to determine the effect of liming on the structure of the rhizosphere microbial community metabolizing root exudates. The lower limit of detection for SIP was determined in soil samples inoculated with a range of concentrations of 13C-labelled Pseudomonas fluorescens and was found to lie between 10(5) and 10(6) cells per gram of soil. The technique was capable of detecting microbial communities actively assimilating root exudates derived from recent photo-assimilate in the field. Denaturing gradient gel electrophoresis (DGGE) profiles of bacteria, archaea and fungi derived from fractions obtained from caesium trifluoroacetate (CsTFA) density gradient ultracentrifugation indicated that active communities in limed soils were more complex than those in unlimed soils and were more active in utilization of recently exuded 13C compounds. In limed soils, the majority of the community detected by standard RNA-DGGE analysis appeared to be utilizing root exudates. In unlimed soils, DGGE profiles from 12C and 13C RNA fractions differed, suggesting that a proportion of the active community was utilizing other sources of organic carbon. These differences may reflect differences in the amount of root exudation under the different conditions.

Bacteria↗
PubMed1984

The fate of methoxychlor in soils and transformation by soil microorganisms.

Methoxychlor was found to be sufficiently persistent in soil and its residues were present even 18 months after the soil treatment. Saprophytes, fungi and actinomyces were unaffected by varying concentrations of methoxychlor, azotobacter however was susceptable. Soil strains isolated did not utilize methoxychlor as a sole carbon source except for 9 cultures belonging to the genera Bacillus, Acinetobacter and Rhodococcus which carried out the complete dechlorination, demethylation and splitting of one of methoxychlor aromatic rings. Anaerobic conditions were more favorable for methoxychlor biodegradation by soil and pure microbial cultures.

Acinetobacter↗
PubMed1984

Use of a computer to group actinomycetes for studies on the ecology of soil microorganisms.

A computer program has been prepared for grouping soil actinomycetes into cluster groups based on the presence or absence of aerial mycelium, the color of soluble pigment, and the shade of color of surface and reverse mycelium. The program automatically condenses cultures with wide ranges of characteristics into a limited number of groups and provides a permanent record so that comparisons can be made among experiments performed over a span of time. The program permits the grouping of large numbers of cultures with minimal laboratory effort and has proven useful in defining some of the ecological factors that lead to changed actinomycete populations in soils.

Actinomycetales↗
PubMed1972

Technique for measuring 14 CO 2 uptake by soil microorganisms in situ.

Uptake of (14)CO(2) in soils due to algae or sulfur-oxidizing bacteria was examined by incubation of soil samples with gaseous (14)CO(2) and subsequent chemical oxidation of biologically fixed radioactive isotope to (14)CO(2) for detection with a liquid scintillation counting system. The (14)CO(2) was added to the soil in the gas phase so that no alteration of the moisture or ionic strength of the soil occurred. Wet oxidation of radioactive organic matter was carried out in sealed ampoules, and the (14)CO(2) produced was transferred to a phenethylamine-liquid scintillation counting system with a simply constructed apparatus. The technique is inexpensive and efficient and does not require elaborate traps since several possible interfering factors were found to have no harmful effects. Experiments in coal mine regions and in geothermal habitats have demonstrated the ecological applicability of this technique for measurement of CO(2) fixation by sulfur-oxidizing bacteria and soil algae.

Bacteria↗
PubMed1989

[Transformation of xenobiotics by soil microorganisms and their potential distribution].

Xenobiotics, i.e., unnaturally occurring organic substances, become transformed in soils, waters and ground water aquifers primarily by co-metabolism or by physico-chemical processes. The persistence of both xenobiotics and natural substances, i.e., time required for a 95% disappearance of the original compounds, is dependent on the chemical and physical characteristics of a compound itself (its molecular recalcitrance), on soil properties and conditions, and on the relationships of these factors. Among the specific factors which influence the persistence of individual compounds belong both natural and anthropogenic "non-physiological" characteristics and structures. Naturally occurring compounds become transformed metabolically, those with a xenobiotic character mainly co-metabolically. The degradation kinetics for both types of compounds have an exponential character, and according to a semi-logarithmic figure, it is a first order function (i.e., mineralization or transformation have a linear character). The co-metabolic processes depend closely on the concentration of the given compound in soil solution as well as on the general microbial activity. Metabolically utilizable compounds may serve microorganisms as sources of C, N, and eventually also of P and energy, after the necessary enzymes have become induced and synthetized. Co-metabolical compounds may not have these functions or microorganisms may require a long period to become adapted to them. In general, all means which support the microbial activity, may also support the co-metabolical transformations in the soil. This is especially true for aeration and manuring of soil both of which stimulate unspecifically the proliferation and activity of microorganisms, and indirectly also a co-metabolism of xenobiotics.

Bacteria↗