Identification of non-pseudomonad bacteria from fruit bodies of wild agaricales fungi that detoxify tolaasin produced by Pseudomonas tolaasii

Bacterial isolates from wild Agaricales fungi detoxified tolaasin, the inducer of brown blotch disease of cultivated mushrooms produced by Pseudomonas tolaasii. Mycetocola tolaasinivorans and Mycetocola lacteus were associated with fruit bodies of wild Pleurotus ostreatus and wild Lepista nuda, respectively. Tolaasin-detoxifying bacteria belonging to other genera were found in various wild mushrooms. An Acinetobacter sp. was isolated from fruit bodies of Tricholoma matsutake, Bacillus pumilus was isolated from Coprinus disseminatus, and Sphingobacterium multivorum was isolated from Clitocybe clavipes. A Pedobacter sp., which seemed not be identifiable as any known bacterial species, was isolated from a Clitocybe sp. Tolaasin-detoxifying bacteria identified thus far were attached to the surface of mycelia rather than residing within the fungal cells. M. tolaasinivorans, M. lacteus, B. pumilus, the Pedobacter sp., and S. multivorum efficiently detoxified tolaasin and strongly suppressed brown blotch development in cultivated P. ostreatus and Agaricus bisporus in vitro, but the Acinetobacter sp. did so less efficiently. These bacteria may be useful for the elucidation of mechanisms involved in tolaasin-detoxification, and may become biological control agents of mushroom disease.     

Characterization of psychrotolerant heterotrophic bacteria from Finnish Lapland

A total of 331 aerobic heterotrophic bacterial strains were isolated from various ecosystems of Finnish Lapland (68-69 degrees N) including forest soil, arctic alpine-tundra soil, stream water, lake and mire sediments, lichen and snow algae. Whole cell fatty acid and 16S rRNA gene sequence analysis and microscopy indicated that the isolates were dominated by Gram-negative bacteria, while only 20 Gram-positive strains were isolated. Based on 16S rRNA gene sequences the isolates were members of alpha-, beta-, gamma-Proteobacteria, Gram-positives with low G+C content, Actinobacteria and the Cytophaga/Flexibacter/Bacteroides group. More than one-third of the isolates could be tentatively identified as Pseudomonas spp. which were particularly abundant in the alpine-tundra soils where they represented 60% of all isolates. Other frequently isolated Gram-negative taxa were Burkholderia sp., Collimonas sp., Pedobacter sp., Janthinobacter sp., Duganella sp., Dyella sp. and Sphingomonas sp. Growth temperature ranges and hydrolytic enzyme activities of selected ca.100 strains were screened. The strains were psychrotolerant growing generally at temperatures ranging from 0 to 30 degrees C, as 82% of the isolates grew at 0 degrees C while only 7% grew at 35 degrees C. Protease and lipase activities at 5 degrees C were detected in more than half of the strains while approximately 20% of the strains possessed amylase and/or cellulase activities.     

海洋动植物共附生微生物的分离和抗菌活性研究

从海参、海胆、海葵、海兔、石莼、羊栖菜、裙带菜分离得到125种共附生海洋微生物,以6种敏感菌为指示菌,从中获得具有抑菌活性的细菌21株,放线菌8株,真菌2株。21株抑菌海洋细菌中芽孢杆菌属为7株,占33．3％,弧菌属为11种,占52．2％,其余3株为假单孢杆菌属,占14．5％。8株抑菌海洋放线菌中链霉菌属为5株,占62．5％,小单孢菌属为3株,占36．5％。2株抑菌海洋真菌均为青霉属。     

Guar gum: a cheap substitute for agar in microbial culture media

AIMS: To determine the possibility of using guar gum, a colloidal polysaccharide, as a cheap alternative to agar for gelling microbial culture media. METHODS AND RESULTS: As illustrative examples, 12 fungi and 11 bacteria were cultured on media solidified with either guar gum or agar. All fungi and bacteria exhibited normal growth and differentiation on the media gelled with guar gum. Microscopic examination of the fungi and bacteria grown on agar or guar gum gelled media did not reveal any structural differences. However, growth of most of the fungi was better on guar gum media than agar, and correspondingly, sporulation was also more advanced on the former. Bacterial enumeration studies carried out for Serratia sp. and Pseudomonas sp. by serial dilution and pour-plate method yielded similar counts on both agar and guar gum. Likewise, a selective medium, succinate medium used for growth of Pseudomonas sp. did not support growth of Bacillus sp. when inoculated along with Pseudomonas on both agar or guar gum supplemented medium. CONCLUSIONS: Guar gum, a galactomannan, which is 50 times cheaper than Difco-bacto agar, can be used as a gelling agent in place of agar in microbial culture media. SIGNIFICANCE AND IMPACT OF THE STUDY: As the media gelled with guar gum do not melt at temperature as high as 70 degrees C, these can be used for isolation and maintenance of thermophiles.     

葡萄连作对土壤细菌和真菌种群的影响

分别采集种植葡萄30年的连作园和3年的新植园根围土、非根围土及葡萄园周边的空地土壤,采用PCR DGGE技术,研究葡萄连作对土壤细菌和真菌种群结构及多样性的影响,并对分离出的优势种扩增条带进行测序.结果表明：葡萄连作后土壤细菌和真菌的多样性增加,且根围土壤的微生物多样性高于非根围土壤.聚类分析显示：葡萄长期连作后根围与非根围土壤细菌和真菌的种群结构趋于一致,两者不同于空地土壤;而短期种植葡萄的根围土壤细菌和真菌的种群结构不同于非根围土壤和空地土壤.与新植园相比,连作园根围土壤中微生物种群结构发生较大变化,细菌中Flavobacterium sp.（DQ339585）和Bacillus sp.（AY039821）种群数量减少,Pedobacter sp.（AJ871084）种群数量增多;真菌中Omphalina farinolens（EF413029）出现,Pestalotiopsis sp.(DQ657877,DQ657875,DQ657871）、Phacidium lacerum（DQ470976）和Lecythophora decumbens（AF353597）种群数量减少,Pilidium acerinum voucher（AY48709）种群数量增多.其中Bacillus sp.、Flavobacterium sp.和Pestalotiopsis sp.对病原菌具有颉颃作用,连作园根围土中上述微生物种群数量的减少,不利于葡萄对病原菌的颉颃;Pilidium acerinum voucher数量的增加可能与葡萄连作后病害加重有关.     

A simple strategy for investigating the diversity and hydrocarbon degradation abilities of cultivable bacteria from contaminated soil

The use of indigenous bacterial strains is a valuable bioremediation strategy for cleaning the environment from hydrocarbon pollutants. The isolation and selection of hydrocarbon-degrading bacteria is therefore crucial for obtaining the most promising strains for site decontamination. Two different media, a minimal medium supplemented with a mixture of polycyclic aromatic hydrocarbons and a MS medium supplemented with triphenyltetrazolium chloride, were used for the isolation of bacterial strains from two hydrocarbon contaminated soils and from their enrichment phases. The hydrocarbon degradation abilities of these bacterial isolates were easily and rapidly assessed using the 2,6-dichlorophenol indophenol assay. The diversity of the bacterial communities isolated from these two soil samples and from their enrichment phases was evaluated by the combination of a bacterial clustering method, fluorescence ITS-PCR, and bacterial identification by 16S rRNA sequencing. Different PCR-based assays were performed in order to detect the genes responsible for hydrocarbon degradation. The best hydrocarbon-degrading bacteria, including Arthrobacter sp., Enterobacter sp., Sphingomonas sp., Pseudomonas koreensis, Pseudomonas putida and Pseudomonas plecoglossicida, were isolated directly from the soil samples on minimal medium. The nahAc gene was detected only in 13 Gram-negative isolates and the sequences of nahAc-like genes were obtained from Enterobacter, Stenotrophomonas, Pseudomonas brenneri, Pseudomonas entomophila and P. koreensis strains. The combination of isolation on minimal medium with the 2,6-dichlorophenol indophenol assay was effective in selecting different hydrocarbon-degrading strains from 353 isolates.     

Inter-specific Interactions Between Carbon-limited Soil Bacteria Affect Behavior and Gene Expression

Recent publications indicate that inter-specific interactions between soil bacteria may strongly affect the behavior of the strains involved, e.g., by increased production of antibiotics or extracellular enzymes. This may point at an enhanced competitive ability due to inter-specific triggering of gene expression. However, it is not known if such inter-specific interactions also occur during competition for carbon which is the normal situation in soil. Here, we report on competitive interactions between two taxonomically non-related bacterial strains, Pseudomonas sp. A21 and Pedobacter sp. V48, that were isolated from a dune soil. The strains showed strong effects on each other’s behavior and gene expression patterns when growing together under carbon-limited conditions on agar. The most pronounced observed visual changes in mixed cultures as compared to monocultures were (1) strong inhibition of a bioindicator fungus, suggesting the production of a broad-spectrum antibiotic, and (2) the occurrence of gliding-like movement of Pedobacter cells. Two independent techniques, namely random arbitrary primed-PCR (RAP-PCR) and suppressive subtractive hybridization (SSH), identified in total 24 genes that had higher expression in mixed cultures compared to monocultures. Microbial interactions were clearly bidirectional, as differentially expressed genes were detected for both bacteria in mixed cultures. Sequence analysis of the differentially expressed genes indicated that several of them were most related to genes involved in motility and chemotaxis, secondary metabolite production and two-component signal transduction systems. The gene expression patterns suggest an interference competition strategy by the Pseudomonas strain and an escape/explorative strategy by the Pedobacter strain during confrontation with each other. Our results show that the bacterial strains can distinguish between intra- and inter-specific carbon competition.     

松材线虫对其携带的细菌繁殖的影响

1.引言松材线虫病（Bursaphelenchus xylophilus）是松树的一种毁灭性病害,在日本、中国、韩国和北美、尼日利亚和葡萄牙等国家蔓延,造成了巨大经济损失,其中以日本和中国受害最重.一直认为松材线虫是引起该病的唯一病原,但近十几年来的研究发现,细菌在致病过程中可能起着重要作用,相继从病木和松材线虫体上分离到能对黑松苗有致萎活性的细菌.赵博光等首次根据实验提出松材线虫病是线虫和细菌共同侵染引起的复合侵染病害的假说,并在以后的试验中得到了验证.关于松材线虫对其细菌繁殖的影响研究鲜有报道.本试验采用从感病松树上分离并鉴定了的细菌菌株中选取假单胞属7株、其它属的细菌菌株3株,     

贪婪倔海绵中抗菌活性细菌的筛选及初步鉴定

采用平板涂布法从我国南海三亚周边海域贪婪倔海绵（Dysidea avara）中分离海绵共附生细菌,采用金黄色葡萄球菌、大肠埃希氏菌、荧光假单胞菌、枯草芽孢杆菌、白假丝酵母、宛氏拟青霉、黑曲霉7种指标菌进行抑菌试验筛选抗菌活性菌,同时对于得到的活性菌进行生理生化鉴定。共分离获得个149个细菌菌株,发现20株具有抑制真菌和革兰氏阳性细菌的活性,占细菌总数的13．4％。经过细菌形态观察和生理生化试验,发现此20株活性菌属于革兰氏阳性芽孢杆菌属（Bacillus sp．）。     

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.     

Characterization of plant growth promoting rhizobacteria isolated from polluted soils and containing 1-aminocyclopropane-1-carboxylate deaminase

Fifteen bacterial strains containing 1-aminocyclopropane-1-carboxylate (ACC) deaminase were isolated from the rhizoplane of pea (Pisum sativum L.) and Indian mustard (Brassica juncea L.) grown in different soils and a long-standing sewage sludge contaminated with heavy metals. The isolated strains were characterized and assigned to various genera and species, such as Pseudomonas brassicacearum, Pseudomonas marginalis, Pseudomonas oryzihabitans, Pseudomonas putida, Pseudomonas sp., Alcaligenes xylosoxidans, Alcaligenes sp., Variovorax paradoxus, Bacillus pumilus, and Rhodococcus sp. by determination of 16S rRNA gene sequences. The root elongation of Indian mustard and rape (Brassica napus var. oleifera L.) germinating seedlings was stimulated by inoculation with 8 and 13 isolated strains, respectively. The bacteria were tolerant to cadmium toxicity and stimulated root elongation of rape seedlings in the presence of 300 microM CdCl2 in the nutrient solution. The effect of ACC-utilising bacteria on root elongation correlated with the impact of aminoethoxyvinylglycine and silver ions, chemical inhibitors of ethylene biosynthesis. A significant improvement in the growth of rape caused by inoculation with certain selected strains was also observed in pot experiments, when the plants were cultivated in cadmium-supplemented soil. The biomass of pea cv. Sparkle and its ethylene sensitive mutant E2 (sym5), in particular, was increased through inoculation with certain strains of ACC-utilising bacteria in pot experiments in quartz sand culture. The beneficial effect of the bacteria on plant growth varied significantly depending on individual bacterial strains, plant genotype, and growth conditions. The results suggest that plant growth promoting rhizobacteria containing ACC deaminase are present in various soils and offer promise as a bacterial inoculum for improvement of plant growth, particularly under unfavourable environmental conditions.     

Attachment of different soil bacteria to arbuscular mycorrhizal fungal extraradical hyphae is determined by hyphal vitality and fungal species

Attachment of certain bacteria to living arbuscular mycorrhizal fungal extraradical hyphae may be an important prerequisite for interactions between these microorganisms, with implications for nutrient supply and plant health. The attachment of five different strains of gfp-tagged soil bacteria (Paenibacillus brasilensis PB177 (pnf8), Bacillus cereus VA1 (pnf8), Pseudomonas fluorescens SBW25 :: gfp/lux, Arthrobacter chlorophenolicus A6G, and Paenibacillus peoriae BD62 (pnf8)) to vital and nonvital extraradical hyphae of the arbuscular mycorrhizal fungi Glomus sp. MUCL 43205 and Glomus intraradices MUCL 43194 was examined. Arthrobacter chlorophenolicus did not attach to hyphae, whereas the other bacterial strains did to a varying degree. Only P. brasilensis showed greater attachment to vital hyphae than nonvital hyphae of both Glomus species tested. Pseudomonas fluorescens showed a higher attachment to vital compared with nonvital Glomus sp. MUCL 43205 hyphae, whereas this relationship was opposite for attachment to G. intraradices. Both B. cereus and P. peoriae showed higher attachment to nonvital hyphae. This study provides novel evidence that under laboratory conditions soil bacteria differ in their ability to colonize vital and nonvital hyphae and that this can also be influenced by the arbuscular mycorrhizal fungal species involved. The significance of bacterial attachment to mycorrhizal fungal extraradical hyphae is discussed.     

Characteristics of Bacteria from Oilseed Rape in Relation to their Biocontrol Activity against Verticillium dahliae

The potential of bacteria that are adapted to the oilseed rape root environment for use in the biological control of Verticillium dahliae, Kleb was investigated in both controlled and non‐sterile growth conditions. Bacterial strains dominated by the red‐pigmented members of enterobacteriaceae were isolated from thoroughly washed and air‐dried root segments of symptomless young rape plants. Other associated strains found either belonged to Alcaligenes sp., Stenotrophomonas spp. and Pseudomonas spp. (Pseudomonas acidovorans and Pseudomonas putida) or were unidentified according to fatty acid methyl ester profile analysis. A total of 19 strains isolated in this study together with two previously studied strains, Serratia proteamaculans and Pseudomonas chlororaphis, were characterized on the basis of their interactions with V. dahliae and a number of functional characteristics. In line with earlier observations with root‐colonizing fungi also from oilseed rape, all bacterial strains suppressed the pathogen not only directly and but also indirectly in in vitro assays. Mechanisms of suppression were apparently multifold among the strains, but production of hydrogen cyanide does not seem to be involved in indirect inhibition. The majority of the strains possessed the ability to produce cellulases, proteases and phosphatases and some even produced chitinases and induced hypersensitive responses, indicating their potential for nutrient acquisition as well as colonization capacity and active recognition by the plant cells. Investigations in non‐sterile field soil revealed that some strains protected rape plants from V. dahliae partly by delaying symptom development. None of the strains, however, was strongly deleterious to rape growth either in the presence or absence of the pathogen. Light microscopic observations of roots and results based on agar printing techniques revealed the potential of the studied strains to colonize or interfere with the pathogen colonization. This study provides some insight into the evolved relationship of bacterial residents with their host in terms of their potential importance in its fitness.     

Kinetic aspects of inhibition of the phytopathogenic fungi growth by rhizospera bacteria

Kinetics of growth inhibition of fungi Fusarium and Bipolaris caused by bacteria Pseudomonas sp. V-6798 and Azotobacter chroococum V-2272 D on dense nutrient media, both in single-crop system and by coinoculation, was demonstrated. The speed of fungal colonies growth as a function of bacteria concentration in inoculate was shown to be in accordance with the Ierysalimskii modified equation. The degree of antagonistic activity was suggested to be assessed by the constant of inhibition (Ki) and residual rate of fungi growth. Constant of inhibition of fungal growth by bacteria varied within 10-100 cells/ml for observed species. More effective fungistatic influence of bacterial strains in combined culture was observed. Parameters reported in the present study allow comparing the degree of bacteria antifungal activity in vitro. Suggested screening method could be used for selection of bacteria as activity biofungicide and while selecting biomedication for defined plant pathogen disruption.     

Selection of bacteria able to control Fusarium oxysporum f. sp. radicis-lycopersici in stonewool substrate

AIMS: Tomato foot and root rot (TFRR), caused by Fusariumoxysporum f. sp. radicis-lycopersici (Forl), is an economically important disease of tomato. The aim of this study was to develop an efficient protocol for the isolation of bacteria, which controls TFRR based on selection of enhanced competitive root-colonizing bacteria from total rhizosphere soil samples. METHODS AND RESULTS: A total of 216 potentially enhanced bacterial strains were isolated from 17 rhizosphere soil samples after applying a procedure to enrich for enhanced root tip colonizers. Amplified ribosomal DNA restriction analysis, in combination with determination of phenotypic traits, was introduced to evaluate the presence of siblings. One hundred sixteen strains were discarded as siblings. Thirty-eight strains were discarded as potential pathogens based on the sequence of their 16S rDNA. Of the remaining strains, 24 performed equally well or better than the good root colonizer Pseudomonas fluorescens WCS365 in a competitive tomato root tip colonization assay. Finally, these enhanced colonizers were tested for their ability to control TFRR in stonewool, which resulted in seven new biocontrol strains. CONCLUSIONS: The new biocontrol strains, six Gram-negative and one Gram-positive bacteria, were identified as three Pseudomonas putida strains and one strain each of Delftia tsuruhatensis, Pseudomonas chlororaphis, Pseudomonas rhodesiae and Paenibacillus amylolyticus. SIGNIFICANCE AND IMPACT OF THE STUDY: We describe a fast method for the isolation of bacteria able to suppress TFRR in stonewool, an industrial plant growth substrate. The procedure minimizes the laborious screens that are a common feature in the isolation of biocontrol strains.     

毛泡桐内生真菌的分离、拮抗细菌菌株的筛选和鉴定

为寻找新的能产生抗生素的植物内生真菌,采用3种培养基对毛泡桐进行内生真菌的分离,以大肠埃希菌、枯草芽胞杆菌、金黄色葡萄球菌、青枯假单胞菌为指示菌,利用琼脂块法和滤纸片扩散法筛选能抑制细菌的菌株;通过形态特征和ITS序列分析鉴定高活性菌株。结果从毛泡桐的根、茎、叶中共分离得到46株内生真菌,至少能抑制一种指示菌的有9株,其中菌株KLBMP-Pt630、KLBMP-Pt675和KLBMP-Pt686活性较强,鉴定结果显示:KLBMP-Pt630为三线镰刀菌、KLBMP-Pt675为棒曲霉、KLBMP-Pt686属于肉座菌目真菌。     

Removal of phenanthrene from soil by co-cultures of bacteria and fungi pregrown on sugarcane bagasse pith

Sixteen co-cultures composed of four bacteria and four fungi grown on sugarcane bagasse pith were tested for phenanthrene degradation in soil. The four bacteria were identified as Pseudomonas aeruginose, Ralstonia pickettii, Pseudomonas sp. and Pseudomonas cepacea. The four fungi were identified as: Penicillium sp., Trichoderma viride, Alternaria tenuis and Aspergillus terrus that were previously isolated from different hydrocarbon-contaminated soils. Fungi had a statistically significant positive (0.0001相似文献   

柑橘黄龙病赣南脐橙内生菌种群结构分析

【目的】分析赣南脐橙黄龙病植株和健康植株叶片内生菌,对比不同培养条件下培养出的内生菌,为筛选出对柑橘黄龙病原菌有影响的伴生菌奠定理论基础。【方法】通过PCR方法对脐橙中黄龙病菌进行验证,并基于16S r RNA基因高通量测序技术对患病与健康赣南脐橙叶片内生菌以及不同培养基富集培养后的内生菌进行多样性分析。【结果】所采集样品中有5株患病株,5株健康株。5株病株中共同含有的细菌属有13个,其中7个在5株健株中也共同存在。Defluviicoccus属和Granulicella属在病健株植物中都是优势菌属,且在健株中的平均含量高于病株。病株与健株的样品相似度存在明显界线。富集培养后不同样本和不同培养基中菌属分布不同。肠杆菌属(Enterobacter)、短小杆菌属(Curtobacterium)、假单胞菌属(Pseudomonas)和泛菌属(Pantoea)得到了大量富集,不动杆菌属和沙雷氏菌属等9个菌属富集量较少。另外,培养和未培养各样本间未分类菌(Unclassified)含量差异也较大。【结论】赣南脐橙患病植株和健康植株叶片内生菌有着明显差异,黄龙病菌的存在改变了脐橙叶片原有内生细菌的菌群结构。从活体植物组织内直接检测才能得到真正的植物内生菌群落分布情况。通过分析菌群的差异,有望找到与柑橘黄龙病菌生长相关的伴生菌。     

Use of Tn5 Mutants To Assess the Role of the Dissimilatory Nitrite Reductase in the Competitive Abilities of Two Pseudomonas Strains in Soil

We examined the influence of soil aeration state and plant root presence on the comparative survival of wild-type bacteria and isogenic Tn5 (Nir(sup-)) mutants lacking the ability to synthesize nitrite reductase. Two denitrifying Pseudomonas strains with different nitrite reductase types were used. Enumeration of bacteria in sterile and nonsterile soils was based on differential antibiotic resistance. The validity of the bacterial models studied (i.e., equal growth of wild-type and mutant bacteria under aerobic conditions and significantly better growth of wild-type bacteria under denitrifying conditions) was verified in pure-culture studies. In sterile soil, both strains survived better under aerobic than under anaerobic conditions. The lower efficiency of denitrification than O(inf2) respiration in supporting bacterial growth explained this result, and the physical heterogeneity of soil did not strongly modify the results obtained in pure-culture studies. In nonsterile soil, one of the Pseudomonas strains survived better under anaerobic conditions while the other competed equally with the indigenous soil microflora under aerobic and anaerobic conditions. However, when the Nir(sup-)-to-total inoculant ratios (wild type plus Nir(sup-) mutant) were analyzed, it appeared that the presence of nitrite reductase conferred on both Pseudomonas strains a competitive advantage for anaerobic environment or rhizosphere colonization. This is the first attempt to demonstrate with isogenic nondenitrifying mutants that denitrification can contribute to the persistence and distribution of bacteria in fluctuating soil environments.     

Pseudomonas-Saccharomyces interactions: influence of fungal metabolism on bacterial physiology and survival

Fungal-bacterial interactions are ubiquitous, yet their molecular basis is only poorly understood. In this study, a novel beneficial interaction between a strain of Pseudomonas putida and the fungus Saccharomyces cerevisiae was identified. When the bacteria were incubated alone in grape juice or in synthetic medium containing various concentrations of glucose, they lost viability rapidly during stationary phase. However, when the bacteria were incubated in these media in the presence of the fungus, their stationary phase survival improved dramatically. On agar plates containing glucose, the beneficial effects of the fungus were manifested in robust bacterial growth and exopolysaccharide production that led to visible mucoidy. In contrast, bacteria grew poorly and were nonmucoid in such media in the absence of the fungus. By using the available S. cerevisiae deletion library, yeast mutants that were unable to mediate this beneficial interaction were identified. These mutants revealed that the beneficial effect on bacterial physiology and survival was mediated by the ability of the fungus to metabolize the available glucose and consequent effects on the medium's pH. In natural environments where the concentration of glucose is high, it is likely that the presence of fungi has had profound beneficial effects on the physiology and survival of certain P. putida strains throughout their natural history.