ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The fluorescent antibody (FA) technique makes possible an autecological approach to microbial ecology because it permits specific microorganisms to be seen and identified in their natural habitats. A method is reported which further extends the FA technique to the quantification of specific bacteria in aquatic and terrestrial ecosystems. Procedures were developed for the most difficult FA-quantification problem, that of the microorganism growing in soil. The protocol that was evolved included: release of bacteria from soil in a dispersed suspension; flocculation of soil colloids out of suspension; concentration, on a special membrane filter, of the bacteria remaining in a known volume of suspension; staining with appropriate homologous FA; and enumeration of reactive cells by incident light immunofluorescence microscopy.Data are reported on the quantification of several bacteria in soil. FA-counts of Rhizobium japonicum, strain USDA 110, agreed well with viable plate counts as the population developed in sterilized soil. Growth of the same organism in nonsterile soils could be followed only by FA-counts. Growth rates and population features for nonsterile soils differed greatly from those observed in sterile soil or laboratory cultures.Escherichia colidie-off was studied quantitatively in normal, nonsterile soil by selective plating, and by the FA-membrane filter count. Agreement between the two methods was good, but FA counts were high at certain stages, probably due to the rapid accumulation of recently-dead cells. As a final exampleNitrobacterwas enumerated by specific FA-membrane filter counts during nitrification in a partially sterilized soil to relate the dynamics of growth to the conversion of nitrite to nitrate.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Kinetics of microbial mass and productivity were calculated from direct microbial counts on two leaf species during their first year of composition at two contrasting sites. Maximum microbial mass on the Fo litter surface approached 25 g/m2of forest floor or 10 percent of the substrate weight. Corresponding productivity was about 1 g/m2·day. Fungal mass averaged 40 times greater than that of bacteria. Related serial dilution plate counts indicated qualitative aspects of colonization.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Plant tissues of low C:N ratio decomposed in soil with the formation of volatiles which increased growth ofR. solaniin culture and induced pigmentation of its mycelium. The effective plant tissues included vegetable crop residues of C:N <15 and immature grain crop residues (corn, oat, rye, barley, sorghum, buckwheat). Volatiles from decomposing plant tissues of high C:N ratio did not affect the fungus mycelium in any way. The dark pigment, formed in culture, is melanin or a melaninlike pigment. An assay procedure for the pigment is described. The effective volatile is a low molecular weight alkaline fraction containing ammonia and/or an amine soluble in boric acid. Both pigmentation and fungus growth increased in response to greater amouts of effective volatiles. Five isolates ofR. solaniresponded similarly to the volatiles. Saprophytic activity of the fungus in soil, through which effective volatiles were passed, decreased significantly. Viability of the pathogen in buckwheat-stem segments in response to decomposing cabbage tissue vapor decreased over the control by 56 percent. The same vapors reduced colonization of the substrate byR. solanifrom soil by 74 percent.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The initial rates of mineralization of chitin byPseudomonassp. and soil microorganisms were enhanced in media containing glass microbeads, the extent of stimulation being governed by bead size. Size of the glass particles also affected the formation of reducing sugars during chitin decomposition. A thin layer of 29 μm beads placed between the polysaccharide andPseudomonassp. almost totally prevented chitin degradation for 15 days, but the attack was retarded somewhat even with glass particles of larger diameter. No decomposition occurred if a thicker layer of small glass spheres was placed between the substrate and the bacterium.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

This paper is an account of studies at the University of Adelaide onAgrobacterium radiobacter, the bacterium responsible for crown gall induction. The original intention was an ecological study of this organism but first it was necessary to be able to identifyA. radiobacterand count it in its natural environment. It turned out that neither of these requirements was satisfied at the start of the investigation. A taxonomic study of the genusAgrobacteriumhad to be undertaken and this led to the definition of two distinct biotypes 1 and 2 ofA. radiobacter, both containing pathogenic and nonpathogenic forms. Pathogenic biotype 2 agrobacteria are predominantly responsible for crown gall induction in Australia. A medium highly selective for biotype 2 agrobacteria was developed and this enabled their distribution and abundance to be measured.The ecological study provided strong circumstantial evidence that stone-fruit trees became galled only when they were growing in soil with a high ratio of pathogenic to nonpathogenic biotype 2 agrobacteria. This ratio could be changed by inoculating seed at time of sowing, or roots at time of transplanting, with nonpathogenic agrobacteria. Efficient biological control of crown gall was achieved by this inoculation which is now widely practiced by commercial growers in Australia. The mechanism of biological control operates through the production of a bacteriocin by the controlling organism.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

A zero-order (with relation to nitrate concentration) kinetic model for denitrification is presented to illustrate the variability of nitrous oxide concentrations in the soil atmosphere. The percentage of N2O with relation to N2is not greatly affected by temperature changes. Aeration and pH are the two functions causing the greatest variability in N2O production. Though the rates of denitrification increase with increasing pH and decreasing aeration, the percentage of N2O declines: this is attributed to a greater increase in the rate of N2O reduction than in its rate of formation.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Preconditioning of different isolates ofCochliobolus sativuswith specific amino acids was found to alter their growth and sporulation characteristics in culture and markedly reduce their virulence to wheat seedlings. Amino acid conditioning also affected the sensitivity ofC. sativusconidia to soil fungistasis and evidence suggesting a differential stimulation of conidial germination by substances from the roots of wheat varieties that differ in degree of susceptibility to ‘common root rot’ was obtained.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The heterotrophic activity of the soil microbiota (expressed as either CO2production or O2consumption) was determined after the addition of various organic substrates (e.g., saccharides, aliphatic and aromatic acids and aldehydes, amino acids; total of 25 compounds) to soils with which 0, 5, 10, or 20 percent montmorillonite or kaolinite or 5 percent mica-vermiculite had been incorporated. With the exception of aldehydes, the decomposition of which was accelerated by the presence of montmorillonite, no clear relationship was observed between the type of organic substrate and the type of clay mineral added. The initial rate and/or the extent of oxidation were either increased, decreased, or not affected by the addition of different clay minerals. In general, the initial rate of decomposition was influenced more by montmorillonite, whereas the extent of oxidation was affected more by kaolinite.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Morphological characteristics, reserve substance formation, and ecological aspects of the distribution ofBeijerinckiaare discussed.Beijerinckiacells are single or bicellular due to cross wall formation in the middle of the longitudinal direction of the cell. This is a division stage and in growing cultures all intermediates between singular and bicellular forms can be found. Electron micrographs showed that the poly-β-butyrate globules at each end of the cell are enclosed by a membrane and that it is likely that this compound is secreted by the membrane system. Electron micrographs show also the capsule wall enclosing the cells in someBeijerinckiaspecies. AlthoughBeijerinckiahas been found in soils outside the tropics and subtropics, its occurrence in temperate regions is in respect of numbers of cells per gram of soil and the frequency ofBeijerinckia-positive soils negligible compared to its nearly ubiquitous occurrence in the tropics. Although the chemical environment of laterization of soil does not give the full explanation of this phenomenon, the chemical requirements ofBeijerinckiapoint to a relation to the lateritic soil type.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID