Efficacy of burning, tillage, and biocides in controlling bacteria released at field sites and effects on indigenous bacteria and fungi.

Decontamination treatments of burning and biocide application, alone and in combination with tillage, were evaluated for their ability to reduce populations of bacteria applied to the leaves of plants in field plots. In addition, the effects of these control methods on indigenous leaf and soil bacteria and fungi were assessed. Field plots of bush beans (Phaseolus vulgaris), sprayed with the bacterium Pseudomonas syringae, Pseudomonas fluorescens, or Erwinia herbicola, received the following treatments: (i) control, (ii) tillage, (iii) burning, (iv) burning plus tillage (burn-tillage), (v) Kocide (cupric hydroxide), (vi) Kocide plus tillage, (vii) Agri-Strep (streptomycin sulfate), and (viii) Agri-Strep plus tillage. Leaves and soil from the plots were sampled at 1 day before and at 1, 3, 7, 10, 14, 21, and 30 days after application of the decontamination treatments. The burn and burn-tillage treatments produced the most significant reductions in bacterial populations. The Agri-Strep treatment was more effective than the Kocide treatment in eliminating applied bacteria, but neither biocide produced consistent or persistent control. In contrast, the tillage treatment, alone or in combination with the Agri-Strep or Kocide treatments, had a short-term stimulatory effect and increased populations of applied bacteria and also levels of indigenous fungi and bacteria. Agri-Strep and Kocide treatments caused significant reductions in indigenous bacterial populations up to 14 days after application and in indigenous fungal populations on day 7 after application. Our results suggest that conventional plant disease control methods may not provide satisfactory control of genetically engineered microorganisms and indicate a need for further development of effective and selective methods to control release microorganisms at field sites.     

Physical and chemical control of released microorganisms at field sites

An important consideration in the environmental release of a genetically engineered microorganism is the capability for reduction or elimination of microorganism populations once their function is completed or if adverse environmental effects are observed. In this study the decontamination treatments of burning and biocide application, alone and in combination with tilling, were evaluated for their ability to reduce populations of bacteria released on the phylloplane. Field plots of bush beans (Phaseolus vulgaris), sprayed with the bacterium Erwinia herbicola, received the following treatments: control; control + till; burn; burn + till; Kocide (cupric hydroxide); Kocide + till; Agri-Strep (streptomycin sulfate); and Agri-Strep + till. Leaves and soil from the plots were sampled -1, 1, 5, 8, 12, 15, 19, and 27 days after application of the decontamination treatments. Burning produced a significant reduction in the number of E. herbicola, whereas tilling, alone or in combination with the biocide treatments, stimulated a significant increase in E. herbicola populations, which persisted for several weeks. The individual treatments of the biocides, Kocide and Agri-Strep, produced a rate of decline in E. herbicola populations that did not significantly differ from that of the control treatment.     

Long-term effect of mineral fertilizers and amendments on microbial dynamics in an alfisol of Western Himalayas

The microbial dynamics expressed in terms of culturable microbial populations i.e. bacteria, fungi, actinomycetes and Azotobacter were measured after 33 years of continuous application of mineral fertilizers and amendments to an acid alfisol. The bacterial, fungal and Azotobacter populations were maximum in plots treated with mineral fertilizers and FYM (100%NPK+FYM) while actinomycetes population was maximum in mineral fertilizes and lime treated plots (100%NPK+Lime). The bacterial population decreased and fungal population increased with increasing levels of NPK i.e. from 50% to 150%NPK. Bacillus species of bacteria and Gliocladium, Aspergillus and Rhizopus species of fungi were the main dominating culturable microorganisms in all the treatments. The FYM and lime amended plots sustained crop productivity and microbial populations at higher levels than rest of the mineral fertilizer treatments. The nitrogenous fertilizers alone had the most deleterious effect on crop productivity and the biological soil environment.     

Effects of streptomycin,cycloheximide, Fungizone,captan, carbofuran,cygon, and PCNB on soil microorganisms

Eight biocides were chosen to determine whether they had any effects on nontarget organisms in soil and to what extent they would reduce their target populations under laboratory experimental conditions. A simplified microcosm system was utilized in which reduced species arrays that included field populations of either only bacteria and fungi, or bacteria, fungi, and protozoa (no nematodes, arthropods, or plants) were inoculated into sterilized soil. In a second set of experiments, plants were grown in sterilized soil. A bactericide-streptomycin-four fungicides-cycloheximide, Fungizone (amphotericin B), captan, and PCNB (quintozene)-an acaricide-cygon-an insecticide-nematicide-carbofuran-and an insecticide-diazinon-were used. Each biocide had effects on nontarget organisms although the increases or decreases, with respect to the control, were of only limited duration. Reductions in target groups were typically of longer duration. Streptomycin, applied at 1 mg·g^–1 soil, did not decrease bacterial populations during the experimental incubation. At 3 mg·g^–1 soil, streptomycin decreased the numbers of bacteria that grew on tryptone agar, but also reduced active hyphae. Fungizone was the most effective of the 4 fungicides tested in reducing active hyphae. Increased bacterial populations were usually observed following fungal reductions. Carbofuran had the fewest effects on the test organisms (bacteria, fungi, and protozoa). Only an initial stimulation of bacterial and fungal populations was observed with cygon although it also increased NH₄ ⁺-N concentrations in soil during most of the incubation, as did streptomycin and cycloheximide. A transitory increase in fungal populations following a decrease in ciliate numbers was observed in the cygon with grazers treatments. Diazinon reduced all microbial populations and inorganic nitrogen concentrations measured. Cygon and PCNB decreased growth of blue grama plants, while streptomycin reduced shoot weights of blue grama. These results should be useful in assessing the effects of these biocides when applied to more complex systems.     

Microbial Dynamics during Bioremediation of a Crude Oil-Contaminated Coastal Wetland

In 1996, a controlled crude oil application was conducted at a Texas intertidal, coastal wetland to determine the effectiveness of two biostimulation treatments in these sensitive areas. An inorganic nutrient treatment and inorganic nutrient plus a potential electron acceptor (nitrate) treatment were examined. As part of this research, polycyclic aromatic hydrocarbon (PAH)-degrading, aliphatic-degrading, and total heterotrophic microbial numbers were monitored. Using a randomized, complete block design consisting of 21 plots, microbial data from biostimulation treatment plots were statistically compared to oiled control plots to assess treatment differences. Sediment samples from all plots receiving oil showed exponential increases in the numbers of aliphatic (n-alkane) and PAH-degrading microorganisms. This increase was observed at both 0 to 5 cm and 5 to 10 cm sample depths. Statistical analysis, however, revealed no significant differences in the numbers of aliphatic-degrading or PAH-degrading microorganisms between treatment plots and oiled control plots or between treatments on any sample day. The numbers of PAH- and aliphatic-degrading microorganisms returned to near pre-application levels by the end of the monitoring period. Ratios of hydrocarbon-degrading microbes to total heterotrophs also increased as a result of the oil application and returned to pre-application levels by the end of the monitoring period. Overall, the populations of hydrocarbon-degrading microorganisms illustrated a well-documented response to crude oil. However, the addition of the biostimulation treatments did not significantly increase the numbers of aliphatic-degrading, PAH-degrading, or total heterotrophic microorganisms over populations on control plots.     

Effect of bacterial antagonists on lettuce: active biocontrol of Rhizoctonia solani and negligible, short-term effects on nontarget microorganisms

The aim of this study was to assess the biocontrol efficacy against Rhizoctonia solani of three bacterial antagonists introduced into naturally Rhizoctonia-infested lettuce fields and to analyse their impact on the indigenous plant-associated bacteria and fungi. Lettuce seedlings were inoculated with bacterial suspensions of two endophytic strains, Serratia plymuthica 3Re4-18 and Pseudomonas trivialis 3Re2-7, and with the rhizobacterium Pseudomonas fluorescens L13-6-12 7 days before and 5 days after planting in the field. Similar statistically significant biocontrol effects were observed for all applied bacterial antagonists compared with the uninoculated control. Single-strand conformation polymorphism analysis of 16S rRNA gene or ITS1 fragments revealed a highly diverse rhizosphere and a less diverse endophytic microbial community for lettuce. Representatives of several bacterial (Alpha-, Beta- and Gammaproteobacteria, Firmicutes, Bacteriodetes), fungal (Ascomycetes, Basidiomycetes) and protist (Oomycetes) groups were present inside or on lettuce plants. Surprisingly, given that lettuce is a vegetable that is eaten raw, species of genera such as Flavobacterium, Burkholderia, Staphylococcus, Cladosporium and Aspergillus, which contain potentially human pathogenic strains, were identified. Analysis of the indigenous bacterial and endophytic fungal populations revealed only negligible, short-term effects resulting from the bacterial treatments, and that they were more influenced by field site, plant growth stage and microenvironment.     

Population dynamics and gene transfer in genetically modified bacteria in a model microcosm

The horizontal transfer and effects on host fitness of a neutral gene cassette inserted into three different genomic loci of a plant-colonizing pseudomonad was assessed in a model ecosystem. The KX reporter cassette (kanamycin resistance, aph, and catechol 2, 3, dioxygenase, xylE) was introduced on the disarmed transposon mini-Tn5 into: (I) the chromosome of a spontaneous rifampicin resistant mutant Pseudomonas fluorescens SBW25R; (II) the chromosome of SBW25R in the presence of a naturally occurring lysogenic-phage (phage Phi101); and (III) a naturally occurring plasmid pQBR11 (330 kbp, tra+, Hgr) introduced into SBW25R. These bacteria were applied to Stellaria media (chickweed) plants as seed dressings [c. 5 x 104 colony-forming units (cfu)/seed] and the seedlings planted in 16 microcosm chambers containing model plant and animal communities. Gene transfer to pseudomonads in the phyllosphere and rhizosphere was found only in the plasmid treatment (III). Bacteria in the phage treatment (II) initially declined in density and free phage was detected, but populations partly recovered as the plants matured. Surprisingly, bacteria in the chromosome insertion treatment (I) consistently achieved higher population densities than the unmanipulated control and other treatments. Plasmids were acquired from indigenous bacterial populations in the control and chromosome insertion treatments. Plasmid acquisition, plasmid transfer from inocula and selection for plasmid carrying inocula coincided with plant maturation.     

Microbial Population Changes during Bioremediation of an Experimental Oil Spill

Three crude oil bioremediation techniques were applied in a randomized block field experiment simulating a coastal oil spill. Four treatments (no oil control, oil alone, oil plus nutrients, and oil plus nutrients plus an indigenous inoculum) were applied. In situ microbial community structures were monitored by phospholipid fatty acid (PLFA) analysis and 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) to (i) identify the bacterial community members responsible for the decontamination of the site and (ii) define an end point for the removal of the hydrocarbon substrate. The results of PLFA analysis demonstrated a community shift in all plots from primarily eukaryotic biomass to gram-negative bacterial biomass with time. PLFA profiles from the oiled plots suggested increased gram-negative biomass and adaptation to metabolic stress compared to unoiled controls. DGGE analysis of untreated control plots revealed a simple, dynamic dominant population structure throughout the experiment. This banding pattern disappeared in all oiled plots, indicating that the structure and diversity of the dominant bacterial community changed substantially. No consistent differences were detected between nutrient-amended and indigenous inoculum-treated plots, but both differed from the oil-only plots. Prominent bands were excised for sequence analysis and indicated that oil treatment encouraged the growth of gram-negative microorganisms within the α-proteobacteria and Flexibacter-Cytophaga-Bacteroides phylum. α-Proteobacteria were never detected in unoiled controls. PLFA analysis indicated that by week 14 the microbial community structures of the oiled plots were becoming similar to those of the unoiled controls from the same time point, but DGGE analysis suggested that major differences in the bacterial communities remained.     

Microbial population changes during bioremediation of an experimental oil spill.

Three crude oil bioremediation techniques were applied in a randomized block field experiment simulating a coastal oil spill. Four treatments (no oil control, oil alone, oil plus nutrients, and oil plus nutrients plus an indigenous inoculum) were applied. In situ microbial community structures were monitored by phospholipid fatty acid (PLFA) analysis and 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) to (i) identify the bacterial community members responsible for the decontamination of the site and (ii) define an end point for the removal of the hydrocarbon substrate. The results of PLFA analysis demonstrated a community shift in all plots from primarily eukaryotic biomass to gram-negative bacterial biomass with time. PLFA profiles from the oiled plots suggested increased gram-negative biomass and adaptation to metabolic stress compared to unoiled controls. DGGE analysis of untreated control plots revealed a simple, dynamic dominant population structure throughout the experiment. This banding pattern disappeared in all oiled plots, indicating that the structure and diversity of the dominant bacterial community changed substantially. No consistent differences were detected between nutrient-amended and indigenous inoculum-treated plots, but both differed from the oil-only plots. Prominent bands were excised for sequence analysis and indicated that oil treatment encouraged the growth of gram-negative microorganisms within the alpha-proteobacteria and Flexibacter-Cytophaga-Bacteroides phylum. alpha-Proteobacteria were never detected in unoiled controls. PLFA analysis indicated that by week 14 the microbial community structures of the oiled plots were becoming similar to those of the unoiled controls from the same time point, but DGGE analysis suggested that major differences in the bacterial communities remained.     

The effects of pesticides on the diversity of culturable soil bacteria

The numbers of culturable soil bacteria in plots that had received either no pesticides or the full combination (aldicarb, chlorfenvinphos, benomyl, glyphosate, plus chlorotoluron or triadimefon) over a 20 year period were compared. Differences were very small although there were consistently higher numbers on the treated plot, possibly reflecting the greater crop yields which had been reported previously. There was no significant difference in numbers of bacterial colonies with homology to a nif gene probe in soils from the two plots. Genetic fingerprinting of Pseudomonas fluorescens isolates from the plots, using ERIC-PCR, showed that the dominant strains in the two populations were not the same although there was no obvious difference in the degree of diversity. Substrate utilization by microbial populations from the two plots was compared using Biolog plates. The population from the pesticide-treated plot showed a higher rate of substrate utilization which could reflect a slightly higher inoculum of heterotrophic bacteria, but could also indicate greater metabolic diversity in the population.     

稻田实行保护性耕作对水稻产量、土壤理化及生物学性状的影响

在江西双季稻田进行长期田间定位试验,分析了多年保护性耕作对水稻产量、土壤理化性状及生物学性状的影响。连续8a稻田保护性耕作处理的平均产量高于传统耕作4.46%—8.79%,各处理的有效穗数、每穗粒数和结实率均高于对照,而各处理间穗长和千粒重差异不显著。实行稻田保护性耕作处理的土壤容重低于传统耕作3.6%—5.6%,而总孔隙度和毛管孔隙度分别高出传统耕作1.6%—17.4%、2.4%—16.7%。与传统耕作相比,连续8a保护性耕作显著提高了土壤有机质(2.9%—10.0%)、有效磷(4.8%—31.6%)、速效钾(9.7%—25.7%)。在2005年免耕+插秧的土壤真菌数量最多,显著高于对照处理51.6%,免耕+抛秧在2008年达到最大,显著高于对照处理54.1%。2012年免耕+抛秧、免耕+插秧显著高于对照126.1%、121.1%;另外,各处理间过氧化氢酶、脲酶活性均差异不显著。8a间土壤转化酶活性变化范围在0.292—0.451 mg/g之间,其中2005—2007、2012年均是免耕+抛秧达到最大,与对照相比,增加范围为72.7%—137.7%,且差异显著(P0.05)。因此,实行稻田保护性耕作是适合江南丘陵区双季稻区农业可持续发展的有效模式之一,其中免耕+抛秧和免耕+插秧两种方式效果最为显著。     

INDIGENOUS POULTRY FEED MICROFLORA RESPONSE TO ETHYL ALCOHOL AND BUFFERED PROPIONIC ACID ADDITION

The present study was designed to compare ethyl alcohol with buffered propionic acid feed treatment on the survival of indigenous poultry feed bacteria and fungi. The aerobic bacterial poultry feed populations were not substantially reduced by either ethyl alcohol or buffered propionic acid treatments. Likewise, indigenous poultry feed fungal populations also were not markedly reduced by buffered propionic acid treatment of the feed but fungal poultry feed populations exposed to ethyl alcohol treatments were significantly lower (P<0.05) than fungal populations recovered from either control and buffered propionic acid treated feeds. Ethyl alcohol treatment may have potential for reducing fungal contamination in poultry feed.     

Changes in the populations of microorganisms associated with the application of soil amendments to control Sclerotium rolfsii Sacc.

Populations of microorganisms from soil treated with guanidine thiocyanate, guanylurea sulfate, thiourea, or furfural were compared with those of untreated soil. The materials effected quantitative and/or qualitative changes in composition of the soil microflora depending on the compound used. Guanidine thiocyanate (Gt) significantly (p0.05) increased total fungal populations relative to populations of other treatments. Populations of Penicillium purpurogenum were markedly higher in Gt-treated soil. Gt also increased total bacterial populations, and was the only compound that increased actinomycete populations. The relative percentage of Trichoderma harzianum was significantly higher in soil treated with thiourea than in the other treatments. Furfural increased the percentage of P. purpurogenum with respect to total fungi, and was as effective as guanylurea sulfate in increasing chitinolytic bacteria and those in the Pseudomonas cepacia-group. Thiourea most effectively promoted proliferation of coryneform bacteria. Chitinolytic fungi increased synergistically when Gt and guanylurea sulfate were applied in combination.     

Effect of 2,4-Diacetylphloroglucinol Producing,Overproducing, and Nonproducing Pseudomonas fluorescens F113 in the Rhizosphere of Pea

Pseudomonas fluorescens F113lacZY and modified strains carrying different function modifications were assessed for their impact in the rhizosphere of pea. Strain F113lacZY naturally produces the anti-fungal metabolite 2,4-diacetylphloroglucinol (Phl) useful in plant disease control. The first modified strain of F113 was repressed in production of Phl, creating the Phl negative strain F113G22. The second was a plasmid based overproducer of Phl (F113Rif (pCUGP)). Both the F113lacZY and the F113Rif (pCUGP) strains increased the rhizoplane fungal populations, whereas the same strains reduced the rhizosphere soil fungal populations with respect to the control. Similar results were found with the rhizoplane and rhizosphere soil bacterial populations. The F113G22 treatment resulted in a significantly greater indigenous fluorescent Pseudomonas population than the F113lacZY and F113Rif (pCUGP) treatments and a greater total Pseudomonas population than the control, F113lacZY, and F113Rif (pCUGP) treatments. Overproduction of Phl did not affect the establishment of the introduced Pseudomonas population. None of the inocula displaced the indigenous populations, but the F113G22 inocula had an additive effect on the total Pseudomonas population. P (phosphatase), S (sulphatase), and N (urease) cycle enzyme activities were increased while C (glucosidase, NAGase) cycle activities were decreased by the F113lacZY and F113Rif (pCUGP) treatments, suggesting C leakage from the roots. Overall, most effects of inoculation compared to the wild type were found with the non-Phl-producing strain. Overproduction of Phl had little environmental effect in relation to wild-type inocula.     

Cropping practices modulate the impact of glyphosate on arbuscular mycorrhizal fungi and rhizosphere bacteria in agroecosystems of the semiarid prairie

A growing body of evidence obtained from studies performed under controlled conditions suggests that glyphosate use can modify microbial community assemblages. However, few studies have examined the influence of glyphosate in agroecosystems. We examined 4 wheat-based production systems typical of the Canadian prairie over 2 years to answer the following question: Does preseeding of glyphosate impact soil rhizosphere microorganisms? If so, do cropping practices influence this impact? Glyphosate caused a shift in the species dominating the arbuscular mycorrhizal fungal community in the rhizosphere, possibly through the modification of host plant physiology. Glyphosate stimulated rhizobacterial growth while having no influence on saprotrophic fungi, suggesting a greater abundance of glyphosate-tolerant 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in bacteria than in fungi. Glyphosate stimulated rhizosphere bacteria in pea but not in urea-fertilized durum wheat, which is consistent with inhibition of EPSPS tolerance to residual glyphosate through high ammonium levels. Mitigation of the effects of glyphosate on rhizosphere bacteria through tillage suggests a reduction in residual glyphosate activity through increased adsorption to soil binding sites upon soil mixing. The influence of glyphosate on Gram-negative bacteria was mitigated under drought conditions in 2007. Our experiment suggests that interactions between soil fertility, tillage, and cropping practices shape the influence of glyphosate use on rhizosphere microorganisms.     

Microbial decomposition of post-harvest sugarcane residue

A laboratory in situ composting study was conducted as a possible alternative method for the current practice of open air burning of post-harvest sugarcane residue by sugarcane farmers. In situ composting of the sugarcane residue by the indigenous bacteria and fungi was accelerated using molasses as an initial substrate. A one-time application of molasses boosted the soil microbial population. which started to decompose the ligno-cellulosic fractions of the residue. The study showed significant differences in several parameters among the control and molasses applied treatments, namely, visual decomposition of residue, bacterial and fungal population, soil pH, cellulose content, cellulase activity. and soil organic matter. Further study is needed to refine the process for the future application of this technology as a possible alternative to the current practice of open air burning of sugarcane residue by farmers.     

Repeated introduction of genetically modified Pseudomonas putida WCS358r without intensified effects on the indigenous microflora of field-grown wheat

To investigate the impact of genetically modified, antibiotic-producing rhizobacteria on the indigenous microbial community, Pseudomonas putida WCS358r and two transgenic derivatives were introduced as a seed coating into the rhizosphere of wheat in two consecutive years (1999 and 2000) in the same field plots. The two genetically modified microorganisms (GMMs), WCS358r::phz and WCS358r::phl, constitutively produced phenazine-1-carboxylic acid (PCA) and 2,4-diacetylphloroglucinol (DAPG), respectively. The level of introduced bacteria in all treatments decreased from 10(7) CFU per g of roots soon after sowing to less than 10(2) CFU per g after harvest 132 days after sowing. The phz and phl genes remained stable in the chromosome of WCS358r. The amount of PCA produced in the wheat rhizosphere by WCS358r::phz was about 40 ng/g of roots after the first application in 1999. The DAPG-producing GMMs caused a transient shift in the indigenous bacterial and fungal microflora in 1999, as determined by amplified ribosomal DNA restriction analysis. However, after the second application of the GMMs in 2000, no shifts in the bacterial or fungal microflora were detected. To evaluate the importance of the effects induced by the GMMs, these effects were compared with those induced by crop rotation by planting wheat in 1999 followed by potatoes in 2000. No effect of rotation on the microbial community structure was detected. In 2000 all bacteria had a positive effect on plant growth, supposedly due to suppression of deleterious microorganisms. Our research suggests that the natural variability of microbial communities can surpass the effects of GMMs.     

Crop rotation and tillage systems as a proactive strategy in the control of peanut fungal soilborne diseases

Soil management practices can affect the population dynamics of soil microbial communities. Cultural practices can be adequately combined to benefit natural populations of microorganisms that may have a role in biological control (actinomycetes, Trichoderma spp., and Gliocladium spp.), thus contributing to the management of peanut fungal soilborne diseases in a sustainable manner within ecological boundaries. During six agricultural cycles, rhizosphere soil samples were taken from a field subjected to crop rotation (soybean, peanut, and maize), peanut being under two tillage systems (no till, reduced tillage) with the aim of quantifying populations of soil microorganisms. The incidence of diseases caused by soilborne fungi in peanut was determined at harvest. The highest amount of actinomycetes, Trichoderma spp., and Gliocladium spp. were recorded when maize was the preceding crop. Regarding tillage systems, the populations of the three groups of microorganisms were higher in peanut under no tillage than under reduced tillage. Under these conditions, the lowest incidence of peanut blight (Sclerotinia minor) and root rot (strains of Fusarium solani) was observed, suggesting a possible natural control of peanut soilborne pathogens. The quantification of actinomycetes, Trichoderma spp., and Gliocladium spp. was used as a tool to explore the impacts of different management systems on microbial groups that may be involved in the biological control of soilborne diseases, with the aim of combining those practices that improve native populations of possible beneficial microorganisms. This manipulation can provide sustainable management strategies in the control of soilborne diseases, avoiding the use of artificial inoculations of microorganisms, and reducing agrochemical application.     

Growing edible mushrooms: a conversation between bacteria and fungi

Mushroom cropping consists of the development and fructification of different fungal species in soil or selective substrates that provide nutrients and support for the crop. The microorganisms present in these environments strongly influence, and in some cases are required for the growth and fructification of cultivated mushrooms. Some fungi such as truffles and morels form ectomycorrhizal associations with host plants. For these fungi, helper bacteria play an important role in the establishment of plant-fungal symbioses. Selective processes acting on the microbiota present in substrates and soils determine the composition of the microbiota inhabiting the fruit bodies or interacting with fungal hyphae, and both configure the mushroom holobiont, understood as the fungus plus associated microorganisms. Here, we review current knowledge regarding the cross-talk between bacteria and fungi during mushroom cultivation. We highlight the potential use of bioinoculants as agronomical amendments to increase mushroom productivity through growth promotion or as biocontrol agents to control pests and diseases.     

Dynamics of Foliage and Thatch Populations of Introduced Pseudomonas fluorescens and Streptomyces sp. on a Fairway Turf

Populations of bacteria (Pseudomonas fluorescens A506 and Streptomyces sp. strain 93) applied to a creeping bentgrass/annual bluegrass fairway turf were followed over time on leaves and thatch. While introduced populations remained at detectable levels over a period of 11–25 days, they usually declined gradually and did not increase after their application to turf. Streptomyces rapidly disappeared from leaves while P. fluorescens was able to maintain similar population sizes on both thatch and leaves, after an initial decline of about 1-log unit, showing that it was actively colonizing the foliage despite loss of biomass from lawn mowing. Throughout these experiments, populations of indigenous microbes on foliage and thatch remained stable, about 10⁶ and 10⁸ cfu g⁻¹ for fungi and bacteria, respectively, and were not affected by the application of bacterial antagonists. Niche-clearing with hydrogen peroxide, which temporarily reduced the population size of indigenous microorganisms two-fold, caused population size of P. fluorescens to increase approximately ten-fold within 24 h, while it declined by about one log unit on untreated turf. It is concluded that the indigenous microflora competes with introduced bacterial antagonists and interferes with their establishment and persistence on turf. Additional studies with P. fluorescens revealed that its population size was inoculum dose-dependent and that solid top dressing was slightly more efficient than spraying liquid suspension in establishing the antagonist. It was possible to maintain P. fluorescens populations above 10⁵ cfu/g of thatch and leaves for 2 weeks or more with both top-dressing or spraying with about 1 to 3 × 10¹⁰ cfu m⁻².