Fungistatic activity of different Indian soils againstFusarium udum Butler

Summary The fungistatic activity of different Indian soils againstF. udum, causing wilt disease of pigeon-pea, has been assessed in relation to soil pH and organic matter. Correlation co-efficient between soil characteristics and fungistasis has been calculated to evaluate relationship. High fungistatic activity was exhibited generally by the soils having low pH but high organic matter. The soils exhibiting high fungistatic activity againstF. udum have low incidence of wilt disease of pigeon-pea. There was no definite correlation between volatile and non-volatile fungistasis and, therefore, the origins of volatile and non-volatile fungistasis are different. In the usual biological limit pH had insignificant impact on fungistasis.     

The symbiotic bacteria Alcaligenes faecalis of the entomopathogenic nematodes Oscheius spp. exhibit potential biocontrol of plant- and entomopathogenic fungi

Soil-dwelling entomopathogenic nematodes (EPNs) kill arthropod hosts by injecting their symbiotic bacteria into the host hemolymph and feed on the bacteria and the tissue of the dying host for several generations cycles until the arthropod cadaver is completely depleted. The EPN–bacteria–arthropod cadaver complex represents a rich energy source for the surrounding opportunistic soil fungal biota and other competitors. We hypothesized that EPNs need to protect their food source until depletion and that the EPN symbiotic bacteria produce volatile and non-volatile exudations that deter different soil fungal groups in the soil. We isolated the symbiotic bacteria species (Alcaligenes faecalis) from the EPN Oscheius spp. and ran infectivity bioassays against entomopathogenic fungi (EPF) as well as against plant pathogenic fungi (PPF). We found that both volatile and non-volatile symbiotic bacterial exudations had negative effects on both EPF and PPF. Such deterrent function on functionally different fungal strains suggests a common mode of action of A. faecalis bacterial exudates, which has the potential to influence the structure of soil microbial communities, and could be integrated into pest management programs for increasing crop protection against fungal pathogens.     

Microbial changes occurring in soil as a result of storage

Summary Changes in numbers of various microbial groups in the interim between collection and analysis of a tropical soil were determined. Although the number of most organisms decreased as a result of storage, the percentage distribution of several groups increased. The greatest decreases occurred in the top layers of soil. Both the numbers and the relative distribution of actinomycetes increased after storage. The possible significance of this increase in the detection of fungistatic materials in soil is discussed. Numbers of fungi were higher after storage in all soil depths, except in the top layer where essentially no change occurred. The vertical distribution and relative frequency of isolation of fungal species after storage is presented. The percentage distribution of spore-forming and CO₂-tolerant bacteria was higher after storage, but that of CO₂-tolerant fungi was lower.The significance of these results in soil microbiological studies, as well as possible causes of the changes, are discussed.     

Plant Growth Substances Produced by Micro-organisms of Soil and Rhizosphere

S ummary : Micro-organisms isolated from rhizospheres and rhizoplanes of wheat plants, and from root-free soil, produced growth regulating substances with the properties of gibberellins and indolyl-3-acetic acid (IAA). Substances inhibiting extensions of pea plant internodes and lettuce hypocotyls were also produced, especially by bacteria from the root region of seedlings 6 days old. Bacteria producing growth promoting substances were most abundant on roots of older plants. Seedlings grown aseptically with added gibberellic acid (GA₃) and IAA, or grown with a soil inoculum, developed similarly and differed in their morphology from those grown aseptically without additives.     

Soil fungistasis: role of the microbial nutrient sink and of fungistatic substances in two soils.

Sensitivity of conidia of Cochliobolus victoriae to fungistasis decreased markedly following incubation on moist sand for at least 1 h. Germination was greater on Conover loam or on sand being leached with water than on an alkaline clay loam soil known to produce a volatile fungistatic substance. Evolution of 14CO2 began within 3 min after [14C]glucose was applied to the soils; the rate of 14CO2 evolution was faster with Conover loam. Germination of Thielaviopsis basicola conidia per unit of glucose remaining in agar discs initially containing 0-1% glucose, was lower for discs incubated on the clay loam soil than on Conover loam, and was greatest on a bed of sand undergoing aqueous leaching. Germination of ascospores of Neurospora tetrasperma and conidia of C. victoriae was suppressed on discs of washed, Purified Agar or polyacrylamide gel incubated on or over the clay loam soil, but no suppression resulted when discs were incubated on Conover loam. Extensive aeration of either soil did not remove its fungistatic effect. Fungistasis in Conover loam appears to be caused primarily by nutrient deprivation, whereas volatile fungistatic substances may play a major role in the clay loam soil.     

FUNGISTASIS IN SOILS

1. Fungistasis in soil is a widespread phenomenon affecting most fungal propagules, though some are insensitive. In most instances, it is coexistent with the presence of living microorganisms, and is annulled by energy-yielding nutrients. Fungistasis with characteristics similar to that in soil may also occur on leaves of plants. 2. Germination and growth of bacteria and actinomycetes is also restricted in soils. The characteristics of their inhibition appear to be the same as those for fungi. Therefore, the concept of a widespread microbial inhibition in soil can be applied to all three groups of microorganisms. 3. Fungistasis can be detected by various direct methods, or indirectly by methods involving the use of porous or permeable carriers. It may be expressed as a restriction on the final amount of germination (the usual parameter), germination rate (with time), and rate of germ-tube or hyphal growth. Since the expression of fungistasis is often complete in soil, titration with nutrients may be required to distinguish between the sensitivities of different fungi. 4. Fungistasis generally is expressed most strongly at soil moisture contents somewhat less than saturation. Its expression usually is maximal in neutral or slightly alkaline soils. In acidic conditions fungistasis may be lessened because of suppression of bacterial and actinomycete activity. Increased sensitivity of some fungi in soils of pH > 7.0 may be caused by a directly unfavourable effect of pH on the fungus. 5. Fungal species with small spores tend to be highly sensitive to fungistasis. These spores tend to germinate slowly and to require exogenous nutrients for germination. By contrast, species with larger spores and sclerotia often do not require exogenous nutrients for germination. The larger spores tend to germinate rapidly and to exhibit low sensitivity, as compared with small spores. A few nutrient-independent spores are insensitive to fungistasis. At least a part of the difference in sensitivity is related to germination time; spores which germinate slowly compete poorly with the soil micro-flora for their nutrients. 6. Fungistasis is often temporarily annulled by enriching the soil with energy-yielding nutrients. Usually, complex materials such as plant residues are most effective. A few weeks after such treatment, the level of fungistasis may, however, be increased. Annulment of fungistasis by compounds not utilized as energy sources has not yet been demonstrated. 7. Several soils naturally suppressive to Fusarium wilt diseases were more fungistatic to Fusarium than soils conducive to wilt. Potential means by which fungistasis may be manipulated to control root-infecting fungi are (a) through stimulation of germination with nutrients, thus exposing the germ tube to lysis, and (b) by increasing the fungistatic level of soil through appropriate amendments. 8. Volatile substances identified in soils, some of which are potentially inhibitory to fungi include (a) ammonia, which apparently is evolved from ammonium salts in some arid soils of high pH, (b) ethylene, which has been identified in some soils of pH < 7.0 (though high levels of this gas seem to be tolerated by most fungi), (c) allyl alcohol, and (d) other unidentified substances. Non-volatile inhibitors include high molecular weight substances revealed by molecular sieve chromatography of soil extracts. Microbial metabolites such as those present in staled fungal cultures also have been proposed to account for fungistasis. In a few soils fungistasis persists after sterilization because of the presence of inhibitory concentrations of calcium carbonate, iron or aluminium. Inherent in the proposition that inhibitory substances provide the primary mechanism of fungistasis is the concept of a highly complex phenomenon, involving various highly specific inhibitory and counteracting stimulatory substances, with the outcome for the fungus depending on the kinds and relative amounts of each present. 9. By the nutrient-deficiency hypothesis, the level of available nutrients in soil is insufficient to support germination of nutrient-dependent propagules, except in nutrient-rich microsites. Inhibition of nutrient-independent propagules is explained by loss of endogenous nutrients required for germination, through microbial nutrient competition. Evidence for this hypothesis is (a) the imposition of fungistasis on numerous nutrient-independent propagules during incubation on leaching model systems designed to simulate microbial nutrient competition in soil, (b) similar losses of endogenous nutrients occurring on soil and the leaching system, and (c) the fact that soils are chronically deficient in energy in relation to the microbial populations present, with the consequence that enforced inactivity is imposed upon most of the population at any given time for this reason alone, regardless of the presence or absence of fungistatic substances. Journal series article no. 7747 from the Michigan Agricultural Experiment Station.     

Antagonistic interactions among seedborne microflora and dynamics of microbial incidence

Seed treatment of Phaseolus mungo Roxb. with non-volatile metabolites of dominant seed fungi such as Chaetomium indicum Corda and Curvularia lunata (Walker) Boedijn and the antibiotic substances: chetomin, curvularin and brefeldin reduced the percent incidence of microfungi and bacteria but induced the Streptomyces sp. The antagonistic behaviour of seed microflora was assessed in vitro.     

Production of Antimicrobial Substances by Bacteria Isolated from Fermented Table Olives

Summary The production of antimicrobial substances was studied among 195 bacterial isolates from retail table olives. A total 86 isolates tested positive, and they clustered in 10 groups according to their inhibitory spectra. Many isolates (38.37%) produced strong inhibition against all bacteria tested (Listeria innocua, Lactococcus lactis, Bacillus cereus, B. megaterium, Staphylococcus aureus, Micrococcus luteus, Enterococcus faecalis, and Escherichia coli). The selected bacterial isolates were Gram-positive bacteria with rod morphology (62.67%), short rods (26.65%) or cocci (10.67%). Isolates producing antimicrobial substances may be useful as starters to enhance control of table olive fermentation and improve the safety of retail table olives.     

Volatile-mediated antagonism of soil bacterial communities against fungi

Competition is a major type of interaction between fungi and bacteria in soil and is also an important factor in suppression of plant diseases caused by soil-borne fungal pathogens. There is increasing attention for the possible role of volatiles in competitive interactions between bacteria and fungi. However, knowledge on the actual role of bacterial volatiles in interactions with fungi within soil microbial communities is lacking. Here, we examined colonization of sterile agricultural soils by fungi and bacteria from non-sterile soil inoculums during exposure to volatiles emitted by soil-derived bacterial communities. We found that colonization of soil by fungi was negatively affected by exposure to volatiles emitted by bacterial communities whereas that of bacteria was barely changed. Furthermore, there were strong effects of bacterial community volatiles on the assembly of fungal soil colonizers. Identification of volatile composition produced by bacterial communities revealed several compounds with known fungistatic activity. Our results are the first to reveal a collective volatile-mediated antagonism of soil bacteria against fungi. Given the better exploration abilities of filamentous fungi in unsaturated soils, this may be an important strategy for bacteria to defend occupied nutrient patches against invading fungi. Another implication of our research is that bacterial volatiles in soil atmospheres can have a major contribution to soil fungistasis.     

Gas chromatographic detection of anaerobic bacteria from environment.

A rapid method of detection of anaerobic bacteria in environment using gas chromatograph is described. Metabolically produced volatile and non-volatile fatty acid by the anaerobic bacteria are detected gas-chromatographically. Using this technique anaerobic bacteria are detected from soil, air, laboratory and operation theatre environments and drinking water samples. In the polluted drinking water apart from drug resistant E. coli, Clostridium difficile is isolated indicating faecal pollution of drinking water from cases of antibiotic associated pseudomembraneous colitis. The method has great significance in detection of anaerobic bacteria in environment especially in the management of war wounds.     

海洋细菌活性物质的研究进展

由于海洋细菌有产生多种新颖独特的生物活性物质的巨大潜力,使其成为新药筛选的重要资源,在药品开发研究中具有良好的发展前景。综述了海洋细菌中具有药物开发前景的活性物质的研究和应用现状及其存在的问题。     

Fungistatic Intensity of Agricultural Soil Against Fungal Agents and Phylogenetic Analysis on the Actinobacteria Involved

A total of 287 agricultural soil samples collected from 26 provinces or autonomous regions of China were tested on their ability to suppress the conidial germination of nine biocontrol fungal agents. These soil samples showed great differences in the degree to inhibit the germination of conidia (22.8% < mean inhibition rate < 97.5%), but all exhibited fungistatic activities above the moderate levels (mean inhibition rate > 50%) to most of tested fungi. Ten soil samples that have stronger fungistatic intensity (germination inhibition rate > 68.3%) to the target fungi, Trichoderma viride and Paecilomyces lilacinus, were selected to evaluate their soil actinobacteria involved fungistasis in soil. Of the 1,000 isolates from those soil samples, 345 actinobacteria exhibited fungistatic activity to conidial germination of T. viride and P. lilacinus with germination inhibition rates higher than 10%. Sequences encoding 16S rRNA gene of the 345 actinobacteria were analyzed by ARDRA and resulted 44 different ARDRA types. Fifty-six isolates, at least one from each unique ARDRA type, were selected for 16S rDNA sequencing and phylogenetic analysis. Results indicated that the actinobacteria involved in the soil fungistasis had close phylogenetic relationship with the members of Sterptomycetaceae, Microbacteriaceae, Micrococcaceae, and Nocardiacea.     

Interaction of bacteria with mercuric compounds

We investigated the interaction of mercuric compounds with the bacteria Corynebacterium ammoniagenes, Micrococcus luteus, and Mycobacterium smegmatus capable of producing hydroxylamines (R-NOH) and 2-C-methyl-D-erythritol-2,4-cyclopyrophosphate (MECP), which are prone to form free radicals. The interaction of these substances with Hg2+ ions and their dynamics during the mercuric poisoning of bacteria was studied by EPR and NMR. Under stress conditions induced by lowering pH or generation of active oxygen species, the bacteria and, especially, their mutants with enhanced sensitivity to oxidative stress, were found to respond to exposure to 1-3 micrograms/ml HgCl2 and p-chloromercuribenzoate by a several-fold increase in their viability. The data obtained were interpreted in terms of the involvement of the sulfhydryl groups of bacterial surface proteins in this phenomenon. The interaction of bacteria with mercuric compounds may affect the pathogenesis of tuberculosis and other diseases.     

Microbial populations and activities in the rhizoplane of rock-weathering desert plants. I. Root colonization and weathering of igneous rocks

Dense layers of bacteria and fungi in the rhizoplane of three species of cactus (Pachycereus pringlei, Stenocereus thurberi, Opuntia cholla) and a wild fig tree (Ficus palmeri) growing in rocks devoid of soil were revealed by bright-field and fluorescence microscopy and field emission scanning electron microscopy. These desert plants are responsible for rock weathering in an ancient lava flow at La Purisima-San Isidro and in sedimentary rock in the Sierra de La Paz, both in Baja California Sur, Mexico. The dominant bacterial groups colonizing the rhizoplane were fluorescent pseudomonads and bacilli. Seven of these bacterial species were identified by the 16S rRNA molecular method. Unidentified fungal and actimomycete species were also present. Some of the root-colonizing microorganisms fixed in vitro N(2), produced volatile and non-volatile organic acids that subsequently reduced the pH of the rock medium in which the bacteria grew, and significantly dissolved insoluble phosphates, extrusive igneous rock, marble, and limestone. The bacteria were able to release significant amounts of useful minerals, such as P, K, Mg, Mn, Fe, Cu, and Zn from the rocks and were thermo-tolerant, halo-tolerant, and drought-tolerant. The microbial community survived in the rhizoplane of cacti during the annual 10-month dry season. This study indicates that rhizoplane bacteria on cacti roots in rock may be involved in chemical weathering in hot, subtropical deserts.     

Antimicrobial and antibiofilm potential of injectable platelet rich fibrin—a second-generation platelet concentrate—against biofilm producing oral staphylococcus isolates

Injectable Platelet rich fibrin (i-PRF) is a platelet concentrate that has been extensively used for multiple medical purposes and is a valuable adjunct for the regeneration of damaged tissues in surgical procedures. The enriched bioactive substances in i-PRF are responsible for speeding the wound healing process. Infection of biofilm producing bacteria in surgical wounds is becoming a serious threat. Research in this field is focused on new strategies to fight infections and to reduce the healing time. The present study was aimed to evaluate the in vitro antimicrobial and antibiofilm effects of i-PRF against oral pathogenic biofilm producing staphylococcus bacteria isolated from patient with dental and oral abscess. The antibacterial activity of i-PRF, was determined through broth microdilution as minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). i-PRF exhibited bactericidal activity against both non biofilm and biofilm producing bacteria. i-PRF could be potential antimicrobial peptide used to combat postoperative infections caused by biofilm producing staphylococcus.     

Influence of gaseous metabolites of soil bacteria on the multiplication of Listeria monocytogenes and Yersinia pseudotuberculosis

The influence of gaseous metabolites of saprophytic soil bacteria on the growth and multiplication of L. monocytogenes and Y. pseudotuberculosis was studied. The study revealed that all cultures under study exhibited selectively both inhibiting and stimulating action on the multiplication of test cultures. Bacteria of the genera Pseudomonas and Acinetobacter showed the highest inhibiting activitywith respect to the test cultures. Volatile metabolites of bacteria of the genus Aeromonas showed the highest stimulating activity. Methanol, according to the data of chromatographic analysis, supposedly played the main role in this process and was contained in the volatile substances of Aeromonas bacteria in greater amounts than in the volatile substances of Pseudomonas bacteria.     

Monitoring of accelerated naphthalene-biodegradation in a bioaugmented soil slurry

The effect of microbial inoculation on the mineralization of naphthalene in a bioslurry treatment was evaluated in soil slurry microcosms. Inoculation by Pseudomonas putida G7 carrying the naphthalene dioxygenase (nahA) gene resulted in rapid mineralization of naphthalene, whereas indigenous microorganisms in the PAH-contaminated soil required a 28 h adaptation period before significant mineralization occurred. The number of nahA-like gene copies increased in both the inoculated and non-inoculated soil as mineralization proceeded, indicating selection towards naphthalene dioxygenase producing bacteria in the microbial community. In addition, 16S rRNA analysis by denaturing gradient gel electrophoresis (DGGE) analysis showed that significant selection occurred in the microbial community as a result of biodegradation. However, the indigenous soil bacteria were not able to compete with the P. putida G7 inoculum adapted to naphthalene biodegradation, even though the soil microbial community slightly suppressed naphthalene mineralization by P. putida G7.     

Various methodological approaches in controlled screening of antibiotic producers among the group of Coryneform bacteria]

A methodical system for directed screening of cultures producing broad-spectrum antibiotics among soil saprophytic coryneform bacteria was developed. To isolate such cultures, it was recommended to use the glucose-yeast medium supplemented with malt extract (No. 18/3) and soybean-glucose medium with sodium sulfate and cobalt chloride (No. 20/3). The preliminary alkaline treatment of the soil substrates and the use of acidic soil samples were found to favour isolation of the Mycobacterium type cultures. It was recommended to use gram-negative tests microbes with relatively low antibiotic resistance for screening cultures producing broad spectrum antibiotics. Various agarized and liquid fermentation media were compared in regard to detection of antibiotic activity in the soil coryneform bacteria. The corn medium supplemented with protein-vitamin concentrate, glucose, lactose and starch (No. 116) proved to be the most efficient.     

Arbuscular mycorrhizal fungi: a specialised niche for rhizospheric and endocellular bacteria

Arbuscular mycorrhizal (AM) fungi produce an extensive hyphal network which develops in the soil, producing a specialised niche for bacteria. The aim of this paper is to review briefly the interactions shown by these symbiotic fungi with two bacterial groups: (i) the plant-growth promoting rhizobacteria (PGPRs) which are usually associated with fungal surfaces in the rhizosphere, and (ii) a group of endocellular bacteria, previously identified as being related to Burkholderia on the basis of their ribosomal sequence strains. The endobacteria have been found in the cytoplasm of some isolates of AM fungi belonging to Gigasporaceae and offer a rare example of bacteria living in symbiosis with fungi. This revised version was published online in August 2006 with corrections to the Cover Date.     

Distribution of microorganisms lysing Pseudomonas aeruginosa and Staphylococcus aureus in the system of sewage waters

The regularities of lytic microorganisms distribution in domestic sewage have been studied. A reproduction of mesophilic gram-negative bacteria producing lytic substances against Pseudomonas aeruginosa and Staphylococcus aureus has been shown to take place at mechanical cleaning stages. In the primary sediment trap the number and the relative content of microorganisms lysing P. aeruginosa at mean temperature and the number of microorganisms lysing S. aureus are maximum. The number of gram-positive sporogenous bacteria lysing P. aeruginosa under conditions close to thermophilic does not change considerably till the secondary sediment trap and remains comparatively high. Certain stages of purification can be regarded as a source of microorganisms producing lytic substances.