Effect of certain chemicals on soil fungistasis

Summary Fungistatic property of soil sample amended with certain chemicals has been studied. The fungistatic property was found to be highest in soil samples amended with potassium permanganate and copper sulphate. The remaining chemicals also caused different levels of fungistasis. Thus presence of various chemicals in the microbial products seems to be the possible cause of soil fungistasis.     

Ecology of soil fungi of a sal forest with emphasis on fungistasis

Summary An ecological study of the soil micro-fungi in three forest regions of different age was undertaken. The pH of the soil varied from 6.6 to 6.9. Soil samples were collected from three different depthsviz 0–6, 7–12, and 13–18 inches with aseptic precautions and were studied by a dilution-plate method using peptone-dextrose agar with rose bengal for the fungal analysis. Determinations were made of physico-chemical characters of soil such as organic matter, total nitrogen, phosphorus, water-holding capacity and pH of the soil. The organic matter and nitrogen favoured the growth of fungi in the soil. The upper horizon contained more of the organic matter, nitrogen, phosphorus, and perhaps other elements, which in turn favoured the growth of fungi in soil. The number of fungi decreased according to increase in depth of the soil samples. The frequency and abundance of some dominant fungi have been calculated and the fungal population has been represented both qualitatively and quantitatively. The pattern of colonization of nutrient agar by fungi from soil inocula changed with the increase of concentration of staling products produced by earlier established fungal colonies. At the highest concentration of staling the fungi colonizing the agar disks were species ofTrichoderma, Aspergillus, Penicillium, Curvularia, Alternaria andFusarium. The capacity of species to colonize the staled nutrient medium was due partly to tolerance of the metabolic products diffused in agar disks and partly to density of the population in the inoculated soil. The comparative account of germinated spores on unsterilized and sterilized soil and in controlled condition shows that fungistatic activity is higher in unsterilized soil. In Table 4 the F₃, an oldest soil sample has more fungistatic activity than F₁ and F₂, due to more litter deposition on the floor, which increases the population of micro-organisms and fungistatic activity.     

Iron gathering by zoopathogenic fungi

Iron is a metal required by most microorganisms and is prominently used in the transfer of electrons during metabolism. The gathering of iron is, then, an essential process and its fulfillment becomes a crucial pathogenetic event for zoopathogenic fungi. Iron is rather unavailable because it occurs on the earth's surface in its insoluble ferric form in oxides and hydroxides. In the infected host iron is bound to proteins such as transferrin and ferritin. Solubilization of ferric iron is the major problem confronting microorganisms. This process is achieved by two major mechanisms: ferric reduction and siderophore utilization. Ferric reductase is frequently accompanied by a copper oxidase transport system. There is one example of direct ferric iron transport apparently without prior reduction. Ferric reduction may also be accomplished by low molecular mass compounds. Some fungi have evolved a process of iron acquisition involving the synthesis of iron-gathering compounds called siderophores. Even those fungi that do not synthesize siderophores have developed permeases for transport of such compounds formed by other organisms. Fungi can also reductively release iron from siderophores and transport the ferrous iron often by the copper oxidase transport system. There is a great diversity of iron-gathering mechanisms expressed by pathogenic fungi and such diversity may be found even in a single species.     

Observations on soil fungistasis

Summary Fungistasis property of soil samples from forest area, cultivated field, and grassland field has been studied. Soil samples from different depths were collected in summer, rainy, and winter seasons. The effect of amendment of certain fungal isolates, culture filtrate, mycelial extract and certain plant materials in sterilized soil has also been studied. Generally the fungistasis property was found to be higher in soil samples of upper profiles and it gradually decreased with an increase in soil depth in all the three localities. Highest fungistasis was observed during rainy season when fungal population was also found to be higher. Amongst three localities, higher values were always noticed in forest soil samples. Physico-chemical characters seem to play an indirect role in inducing the soil fungistasis. Fungal spores, culture filtrates and mycelial extracts of certain fungi caused different levels of fungistasis in sterilized soil. Sterilized soil samples amended with various plant parts also caused fungistasis after certain period. Thus fungistasis seems to be a combined effect of various factors existing in the soil.     

Studies on soil fungistasis: Effect of certain physical and biological factors

Summary The effect of different physical and biological factors like soil sterilization, incubation period of soil, spore age, amendment of certain fungal species and their metabolites on soil fungistasis has been investigated.Different degree of sterilization affected the fugistasis differently. Soil heating above 80°C completely annulled the fungistasis. No fungistasis was recorded in soil samples steamed for 15 mts in an autoclave.Incubation of soil samples to longer duration resulted in increased fungistasis. Maximum fungistatic value was noted in samples incubated for 15 days at 25±1°C.Spore age also played important role in fungistasis. A positive relation was noted in the spore age and fungistasis upto 30 days of age and thereafter the increase in fungistasis was not well marked.Varying inhibitory effect was noted on the spore germination of the test fungi in relation to amendment of certain fungi individually and in different combinations to the soil.Aspergillus flavus alone and in combination ofAspergillus niger proved most inhibitory. The filtrate of the different fungi also induced fungistasis in soil. In this case alsoA. flavus was most effective.     

Control of zoopathogenic fungi in vitro by polyamine biosynthesis inhibitors.

Effect of inhibitors of polyamine (PA) biosynthesis, alpha-difluoromethylornithine (DFMO), methylglyoxal bis (guanylhydrazone)--MGBG and bis (cyclohexylammonium) sulphate (BCHA) on mycelial growth of three clinically important fungi-Trichophyton mentagrophytes, Microsporum gypseum and Aspergillus flavus was examined in vitro. All inhibitors at concentrations 1 to 50 mM produced greater inhibition of mycelial growth in all fungi tested in a dose-dependent manner. MGBG was the most effective inhibitor, and T. mentagrophytes was the most sensitive fungus to all inhibitors followed by M. gypseum and A. flavus. The results suggested that control of fungal diseases in animals and human beings with specific inhibitors of PA biosynthesis is possible.     

In vitro interactions between Blastomyces dermatitidis and other zoopathogenic fungi

The results of in vitro interactions between colonies of Blastomyces dermatitidis and six other zoopathogenic fungi are reported. The interactions were found to range from neutral with Histoplasma capsulatum and Candida albicans to strongly antagonistic with Microsporum gypseum, Pseudallescheria boydii, and Sporothrix schenckii, and including lysis by Cryptococcus neoformans. These observations suggest that interactions between zoopathogenic fungi may be one of the biotic factors likely to influence the occurrence of B. dermatitidis in natural systems.     

Microbial community composition affects soil fungistasis

Most soils inhibit fungal germination and growth to a certain extent, a phenomenon known as soil fungistasis. Previous observations have implicated microorganisms as the causal agents of fungistasis, with their action mediated either by available carbon limitation (nutrient deprivation hypothesis) or production of antifungal compounds (antibiosis hypothesis). To obtain evidence for either of these hypotheses, we measured soil respiration and microbial numbers (as indicators of nutrient stress) and bacterial community composition (as an indicator of potential differences in the composition of antifungal components) during the development of fungistasis. This was done for two fungistatic dune soils in which fungistasis was initially fully or partly relieved by partial sterilization treatment or nutrient addition. Fungistasis development was measured as restriction of the ability of the fungi Chaetomium globosum, Fusarium culmorum, Fusarium oxysporum, and Trichoderma harzianum to colonize soils. Fungistasis did not always reappear after soil treatments despite intense competition for carbon, suggesting that microbial community composition is important in the development of fungistasis. Both microbial community analysis and in vitro antagonism tests indicated that the presence of pseudomonads might be essential for the development of fungistasis. Overall, the results lend support to the antibiosis hypothesis.     

Effect of treatment of soil with keratinaceous material on soil fungi

In the early periods of soil storage, the total number of fungi almost regularly and significantly increased with the concentration of keratinaceous material (ground buffalo hooves) between 1% and 10%. A concentration of 20% was stimulative after 7 days and became toxic after 15 days and remained so through the end of the experiment. With increase in the storage period, the beneficial effect of all concentrations was lost and in the case of high concentrations (5-20%) toxic ammonia was produced. The occurrence of Scopulariopsis brevicaulis, Cephalosporium acremonium, Chrysosporium tropicum, C. indicum, and C. keratinophilum increased markedly, especially at the higher concentrations of the keratinaceous material and after long periods of incubation. With increase in the concentration of keratinaceous material, the rate of evolution of ammonia from the soil sharply increased during the second week after treatment and fell off sharply during the third and fourth weeks. In soil stored at 35 C, the rate of decline in total fungi after longer periods of incubation was sharper at 35 C than at 25 C. Also the amount of evolved ammonia during the first and the second weeks was almost always higher at 35 C than at 25 C. Fourteen species were tested for keratinolytic activity. Three of them were highly keratinolytic and five moderately so.     

Sensitivity of Malayan isolates of Fusarium to soil fungistasis

Summary Spore germination of various isolates of Fusarium (isolated from Malayan sources) was inhibited when placed on cellulose film in contact with soil moistened with distilled water. Intraspecific variations in sensitivity to mycostasis were recorded suggesting physiological differences between isolates of the same species. The addition of glucose frequently masked the mycostatic factor while autoclaving the soil completely removed it. The growth of fungal mycelium in contact with soil followed a similar pattern and when hyphae grew in contact with autoclaved soil sporulation was frequently observed.The similarities between the results outlined in this investigation and results from different countries is discussed and it is suggested that pathogenic fungi frequently have to overcome soil mycostasis before they can establish themselves in a new environment.     

Colonization capacity of the soil micro-organisms in relation to fungistasis

Summary Evans' tube and cellophane agar-disc techniques were used to evaluate the colonization capacity of the soil microbes and fungistasis, respectively. Spore germination ofAlternaria tenuis, Curvularia geniculata, Helminthosporium rostratum andPestalotia sp. was studied on a natural soil. Aspergillus fumigatus was the pioneer colonizer, followed in the order of decreasing colonizing capacity by,A. flavus, A. niger, A. terreus andPenicillium nigricans. Sensitivity of test spores to soil fungistasis declined in the order,C. geniculata → Pestalotia sp. →A. tenuis → H. rostratum. The fungistatic level of the soil samples decreased gradually from side arms 1 to 7 of the Evans tube, inoculated with unsterilized soil from one end. Studies conducted with an inoculum of four soil fungi (A. fumigatus, A. flavus, A. niger, andP. nigricans) as well as those involving fumigation of Evans tube by CS₂ also proved the greater colonizing capacity ofA. fumigatus. The level of fungistasis followed closely the colonization pattern of this fungus. When added individually to the soil, all fungi were able to inhibit spore germination of test fungi to some degree or other.     

Effect of cadmium on growth of potentially pathogenic soil fungi

The effect of Cd on the mycelial growth of some potentially pathogenic soil fungi was investigated. Sixty-four strains from twenty-five fungal species were tested for their susceptibility to Cd. Final colony diameter, radial growth rate and final dry mass of mycelium (for Cd: 1–200 ppm) were measured. EcD₅₀ values were calculated from these parameters. The intra- and interspecific variability in the results obtained is presented. Among the keratinolytic fungal group, the genera Arthrographis, Trichophyton and Chrysosporium (including the Chrysosporium anamorph of Aphanoascus reticulisporus) were the most resistant to Cd. T. mentagrophytes was the most sensitive of all Trichophyton species tested. Among the nonkeratinolytic fungal group, the genera Pseudallescheria, Absida and Rhizopus were highly resistant to Cd. Strains of Aspergillus were more resistant to Cd than strains of Penicillium. Zygomycetes were more resistant to Cd than Ascomycetes with Fungi Imperfecti. Nonkeratinolytic fungi showed higher resistance to Cd than keratinolytic fungi. The two last differences resulted from the extremely high EcD₅₀ values for R. oryzae and A. corymbifera. This revised version was published online in June 2006 with corrections to the Cover Date.     

土壤抑真菌作用与细菌群落结构的关系

自然清洁土壤所具有的抑真菌作用,是健康土壤的一种自然属性,也是土壤质量的重要指标之一,对控制农作物土传病原真菌的爆发具有积极的生态学意义.本试验以中国科学院沈阳生态实验站近10年未受农药和肥料影响的撂荒地土壤作为自然清洁土壤样品,通过高温（对照、100 ℃、110 ℃、121 ℃）处理得到具有不同抑真菌作用的土壤模型,采用PCR DGGE(变性梯度凝胶电泳)方法对上述土壤样品的细菌群落结构进行分析.结果表明：土壤抑真菌作用与土壤细菌群落结构紧密相关;对照清洁土壤抑真菌作用最强,处理后土壤细菌群落结构偏离自然清洁土壤愈远,土壤抑真菌能力愈差;DGGE特异性条带切胶测序结果表明,Sphingomonas asaccharolytica、Nitrospira sp.、Hyphomicrobiaceae sp.、Bacillus megaterium和Micrococcus sp.可能与土壤抑真菌作用密切相关.     

Effect of treatment of soil with keratinaceous material on thermophilic fungi

Fusarium oxysporum f. sp. lycopersici and Rhizoctonal solani were grown in a complete 1.0 mM nutrient solution, and in solutions where Ca, Fe, K, Mg, N, P, and S were either excluded (0.0 mM) or included at depleted levels (0.1 mM) while all other constituents were maintained at 1.0 mM levels. Dry weight of both fungi were determined. For both fungi some of the lowest dry weights were recorded for samples grown in the complete solution. Exclusion of K, Mg, and S significantly increased dry weight of Fusarium. Inclusion at the 0.1 mM level of most components significantly increased Fusarium dry weight over values for both the complete and corresponding excluded nutrient solutions. The exception was S where there was no difference between excluded and 0.1 mM solutions. For Rhizoctonia dry weights in Fe excluded solutions were less than the complete solution, while dry weights in S excluded solutions were greater than the complete solution. At the 1.0 mM level Fe, K, and Mg dry weights were significantly increased over the dry weights produced in both the complete and deficient solutions.