Search

Brettanomyces (Dekkera) bruxellensis is an ascomycetous yeast of major importance in the food, beverage and biofuel industry. It has been isolated from various man-made ecological niches that are typically characterized by harsh environmental conditions such as wine, beer, soft drink, etc. Recent comparative genomics studies revealed an immense intraspecific diversity, but it is still unclear whether this genetic diversity also leads to systematic differences in fermentation performance and (off-)flavor production, and to what extent strains have evolved to match their ecological niche. Here, we present an evaluation of the fermentation properties of eight genetically diverse B. bruxellensis strains originating from beer, wine and soft drinks. We show that sugar consumption and aroma production during fermentation are determined by both the yeast strain and composition of the medium. Furthermore, our results indicate a strong niche adaptation of B. bruxellensis, most clearly for wine strains. For example, only strains originally isolated from wine were able to thrive well and produce the typical Brettanomyces-related phenolic off-flavors 4-ethylguaiacol and 4-ethylphenol when inoculated in red wine. Sulfite tolerance was found as a key factor explaining the observed differences in fermentation performance and off-flavor production. Sequence analysis of genes related to phenolic off-flavor production, however, revealed only marginal differences between the isolates tested, especially at the amino acid level. Altogether, our study provides novel insights in the Brettanomyces metabolism of flavor production, and is highly relevant for both the wine and beer industry. [ABSTRACT FROM AUTHOR]

To meet their carbohydrate requirements, adult parasitoids exploit a broad range of sugar resources, including floral and extrafloral nectar and honeydew. Although honeydew might be the predominant sugar source, especially in agricultural systems, it often is nutritionally inferior to sugar sources like nectar. Given its broad availability, it may be expected that sugar-feeding insects have evolved specialized adaptations to deal with this typically inferior sugar source. This would apply especially to organisms that have a close association with honeydew producers. Here, we hypothesized that parasitoids of honeydew-producing insects should show a pronounced response to sugars, such as fructose, sucrose, melezitose, and trehalose, and to a lesser extent glucose. To test this hypothesis, we investigated sugar consumption, feeding behavior and survival of the aphid parasitoid Aphidius ervi on several sugars (equiweight solutions). Our results show that A. ervi adults consumed typical honeydew sugars (sucrose, fructose, trehalose, and melezitose) the most, while consuming considerably less glucose or melibiose. Rhamnose, which does not occur in aphid honeydew, was not, or was only marginally, consumed. When different sugars were provided at the same time, A. ervi adults preferred sucrose or fructose over glucose or melezitose. Furthermore, pre-exposure to sucrose or fructose significantly reduced subsequent intake of glucose, suggesting an acquired distaste for glucose after being previously exposed to highly preferred sugars such as sucrose and fructose. Altogether, this study shows that A. ervi adults prefer sugars (fructose, melezitose, trehalose, and sucrose) that are overrepresented in aphid honeydew and show a lower preference to one (glucose) that is underrepresented in honeydew. [ABSTRACT FROM AUTHOR]

• Background and Aims In orchid species that have populations occurring in strongly contrasting habitats, mycorrhizal divergence and other habitat-specific adaptations may lead to the formation of reproductively isolated taxa and ultimately to species formation. However, little is known about the mycorrhizal communities associated with recently diverged sister taxa that occupy different habitats. • Methods In this study, 454 amplicon pyrosequencing was used to investigate mycorrhizal communities associating with Epipactis helleborine in its typical forest habitat and with its presumed sister species E. neerlandica that almost exclusively occurs in coastal dune habitats. Samples of the phylogenetically more distant E. palustris, which co-occurred with E. neerlandica, were also included to investigate the role of habitat-specific conditions on mycorrhizal communities. • Results A total of 105 operational taxonomic units (OTUs) of putative orchid mycorrhizal fungi were observed in the three studied species. The majority of these fungi were endophytic fungi of Helotiales and ectomycorrhizal fungi belonging to Thelephoraceae, Sebacinaceae and Inocybaceae. In addition, a large number of other ectomycorrhizal taxa were detected, including Cortinarius, Cenococcum, Tuber, Geopora, Wilcoxina, Meliniomyces, Hebeloma, Tricholoma, Russula and Peziza. Mycorrhizal communities differed significantly between the three species, but differences were most pronounced between the forest species (E. helleborine) and the two dune slack species (E. neerlandica and E. palustris). • Conclusion The results clearly showed that recently diverged orchid species that occupy different habitats were characterized by significantly different mycorrhizal communities and call for more detailed experiments that aim at elucidating the contribution of habitat-specific adaptations in general and mycorrhizal divergence in particular to the process of speciation in orchids. [ABSTRACT FROM AUTHOR]

Comparative analyses of bacterial and archaeal community structures and dynamics in three biogas digesters during start-up and subsequent operation using microwaved, ultrasonicated or untreated waste activated sludge were performed based on 454 pyrosequencing datasets of part of 16S ribosomal RNA sequences and quantitative PCR. The pre-treatment increased the solubility, and thus the availability of the substrate for microbial degradation and significantly affected the succession of the anaerobic community structure over the course of the digestion. Bacteroidetes, Proteobacteria and Firmicutes were the dominant phyla in all digesters throughout operation. Proteobacteria decreased in relative abundance from 23-26 % to 11-13 % in association with enhanced substrate availability. Negative correlations between relative abundance of Alpha-, Beta- and Gammaproteobacteria and the substrate availability and/or biogas production were disclosed in statistical analyses. Clostridiales was the dominant order in Firmicutes, and Clostridiales, Clostridia and Firmicutes relative abundance and richness were shown to positively correlate with substrate availability and biogas generation. Methanogenic communities had a fairly restricted structure, highly dominated by Methanosaeta and Methanobrevibacter phylotypes. A gradual decline in Methanobrevibacter and increased representation of Methanosaeta concilii over time were particularly apparent in the digester receiving untreated waste activated sludge, whereas more diversified archaeal communities were maintained in the pre-treatment digesters. The quantitative PCR analyses revealed a methanogenic community distribution that coincided with the 454 pyrosequencing data. [ABSTRACT FROM AUTHOR]

Identifying the ecological processes that underlie the distribution and abundance of species in microbial communities is a central issue in microbial ecology and evolution. Classical trade-off based niche theories of resource competition predict that co-occurrence in microbial communities is more likely when the residing species show trait divergence and complementary resource use. We tested the prediction that niche differentiation explained the co-occurrence of two yeast species ( M etschnikowia reukaufii and M . gruessii) in floral nectar. Assessment of the phenotypic landscape showed that both species displayed a significantly different physiological profile. Comparison of utilization profiles in single versus mixed cultures indicated that these two species did not compete for most carbon and nitrogen sources. In mixed cultures, M . reukaufii grew better in sucrose solutions and in the presence of the antimicrobial compound digitonin than when grown as pure culture. M . gruessii, on the other hand, grew better in mixed cultures in glucose and fructose solutions. Overall, these results provide clear evidence that M . reukaufii and M . gruessii frequently co-occur in nectar and that they differ in their phenotypic response to variation in environmental conditions, suggesting that niche differentiation and resource partitioning are important mechanisms contributing to species co-occurrence in nectar yeast communities. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi are root symbionts that play a key role in crop growth. A systematic quantitative analysis of the response of crops to arbuscular mycorrhizal inoculation, however, remains to be done. Additionally, little is known regarding the role of mycorrhizal specificity and the diversity of the inoculum on crop growth. Therefore, we collected data from 115 inoculation studies, including 435 experiments. We then used meta-analysis to examine the effect of crop identity, arbuscular mycorrhizal fungus identity, and mycorrhizal diversity on crop biomass increase, following inoculation. Our results show that total crop biomass was on average 34.9 % higher in inoculated versus non-inoculated plants. We found that specific combinations of arbuscular mycorrhizal fungus genera and host plant families were more beneficial for growth promotion as compared to other combinations. Moreover, a single-species inoculum increased crop growth response on average by 41.2 % compared to a multi-species inoculum. Overall, our findings show that a broad range of crops highly benefit from the inoculation with arbuscular mycorrhizal fungi. They also strongly suggest that selecting specific arbuscular mycorrhizal taxa for specific crops is the most promising approach to enhance crop growth. There is no 'one-size-fits-all' arbuscular mycorrhizal fungus. Finally, and at least in stable and controlled environments, inoculation with a single arbuscular mycorrhizal species is more effective, compared to inoculation with a mixture of different arbuscular mycorrhizal taxa. This may be explained by fungi superior in extraradical growth, but less beneficial to the host, that outcompete the more mutualistic fungi. Therefore, it may be beneficial to maintain a high dominance of one beneficial arbuscular mycorrhizal taxon in simplified agricultural systems. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal fungi (AMF) play a key role in the functioning of agricultural ecosystems. Therefore, understanding how the application of fertilizers, a common management practice, affects AMF communities is of major importance. Here we aimed to: (i) experimentally test whether different amounts and forms of phosphorus (P) fertilizer affect AMF diversity and community composition associated with the roots of apple trees ( Malus domestica); (ii) identify differences in tolerance to P fertilization between AMF taxa. Methods: We used 454-pyrosequencing of the small subunit rRNA gene amplicons to quantify AMF diversity and community composition in root samples obtained from a three year field experiment, with two inorganic, three slow-release P fertilization and one control treatment. Results: The slow-release fertilizer treatments showed significantly higher AMF richness and differed in community composition compared to the inorganic fertilizer treatments. The distribution of AMF OTUs showed a significantly nested pattern. Additionally, AMF communities in the inorganic fertilizer treatments were a subset of the communities in the slow-release fertilizer treatments. Conclusions: We demonstrate that application of slow-release fertilizers promoted AMF diversity in the roots of cultivated apple trees in comparison to the other treatments. The application of inorganic fertilizers elevated levels of plant-available P in the soil and selected only a small subset of abundant AMF, resulting in a lower AMF diversity. This may result in AMF communities dominated by inferior AMF mutualists. [ABSTRACT FROM AUTHOR]

The widespread use of azole antifungals in medicine and agriculture and the resulting long-persistent residues could potentially affect beneficial fungi. However, there is very little information on the tolerance of non-target environmental fungi to azoles. In this study, we assessed the susceptibility of diverse plant- and insect-associated yeasts from the Metschnikowia clade, including several ecologically important species, to widely used medical and agricultural azoles (epoxiconazole, imazalil, ketoconazole and voriconazole). A total of 120 strains from six species were tested. Minimum inhibitory concentrations (MICs) were determined by the EUCAST broth microdilution procedure after some necessary modifications were made. The majority of species tested were highly susceptible to epoxiconazole, ketoconazole and voriconazole (>95% of strains showed MICs = 0.125 mg l-1). Most strains were also very susceptible to imazalil, although MIC values were generally higher than for the other azoles. Furthermore, certain Metschnikowia reukaufii strains displayed a 'trailing' phenotype (i.e. showed reduced but persistent growth at antifungal concentrations above the MIC), but this characteristic was dependent on test conditions. It was concluded that exposure to azoles may pose a risk for ecologically relevant yeasts from the Metschnikowia clade, and thus could potentially impinge on the tripartite interaction linking these fungi with plants and their insect pollinators. [ABSTRACT FROM AUTHOR]