Environmental metabarcoding reveals contrasting belowground and aboveground fungal communities from poplar at a Hg phytomanagement site

Characterization of microbial communities in stressful conditions at a field level is rather scarce, especially when considering fungal communities from aboveground habitats. We aimed at characterizing fungal communities from different poplar habitats at a Hg-contaminated phytomanagement site by using Illumina-based sequencing, network analysis approach, and direct isolation of Hg-resistant fungal strains. The highest diversity estimated by the Shannon index was found for soil communities, which was negatively affected by soil Hg concentration. Among the significant correlations between soil operational taxonomic units (OTUs) in the co-occurrence network, 80% were negatively correlated revealing dominance of a pattern of mutual exclusion. The fungal communities associated with Populus roots mostly consisted of OTUs from the symbiotic guild, such as members of the Thelephoraceae, thus explaining the lowest diversity found for root communities. Additionally, root communities showed the highest network connectivity index, while rarely detected OTUs from the Glomeromycetes may have a central role in the root network. Unexpectedly high richness and diversity were found for aboveground habitats, compared to the root habitat. The aboveground habitats were dominated by yeasts from the Lalaria, Davidiella, and Bensingtonia genera, not detected in belowground habitats. Leaf and stem habitats were characterized by few dominant OTUs such as those from the Dothideomycete class producing mutual exclusion with other OTUs. Aureobasidium pullulans, one of the dominating OTUs, was further isolated from the leaf habitat, in addition to Nakazawaea populi species, which were found to be Hg resistant. Altogether, these findings will provide an improved point of reference for microbial research on inoculation-based programs of tailings dumps

Yeast Methylotrophy and Autophagy in a Methanol-Oscillating Environment on Growing Arabidopsis thaliana Leaves

The yeast Candida boidinii capable of growth on methanol proliferates and survives on the leaves of Arabidopsis thaliana. The local methanol concentration at the phyllosphere of growing A. thaliana exhibited daily periodicity, and yeast cells responded by altering both the expression of methanol-inducible genes and peroxisome proliferation. Even under these dynamically changing environmental conditions, yeast cells proliferated 3 to 4 times in 11 days. Among the C1-metabolic enzymes, enzymes in the methanol assimilation pathway, but not formaldehyde dissimilation or anti-oxidizing enzymes, were necessary for yeast proliferation at the phyllosphere. Furthermore, both peroxisome assembly and pexophagy, a selective autophagy pathway that degrades peroxisomes, were necessary for phyllospheric proliferation. Thus, the present study sheds light on the life cycle and physiology of yeast in the natural environment at both the molecular and cellular levels

Multiple timescale variations and controls of soil respiration in a tropical dry dipterocarp forest, western Thailand

This study aims to improve our understanding of temporal variations and controlling factors of soil respiration (R-s) and its components (microbial respiration or R-m and root respiration or R-b) in an Asian tropical seasonal forest at diurnal, seasonal and annual timescales in relation to biotic and abiotic controls. R-s was studied by the trenching method in a seasonal dry diptercarp forest, western Thailand. An automated soil chamber system was used to produce hourly data of R-s during 2008-2011. Analysis of R-s in relation to both biotic and abiotic factors was carried out to understand its temporal variations at different timescales. R-m was the main contributor to overall magnitude and variability of R-s. Soil temperature alone was the main driver of diurnal variation, while the combination of soil moisture and soil temperature determined the seasonal variations. The amount of R-s was also related to the fine root (< 2 mm) and microbial biomass at seasonal timescales. Due to the small inter-annual variations in soil temperature and moisture, total soil respiration among the 4 years was not significantly different (p < 0.05). The annual totals for R-s during 2008-2011 were 3.20, 3.89, 3.52, 4.14 kgCO(2) m(-2) years(-1), respectively. The 4-year average ratio of R-m (trenched) to R-s (untrenched) was 66 +/- 4 %. R-m plays a crucial role in determining the magnitude (large ratio between R-m and R-s) and temporal variations of R-s. In this forest ecosystem, high seasonal variations in R-s were observed and were mainly attributed to the response of R-m to moisture

Xylitol production by Candida parapsilosis under fed-batch culture

Xylitol production by Candida parapsilosis was investigated under fed-batch cultivation, using single (xylose) or mixed (xylose and glucose) sugars as substrates. The presence of glucose in the medium induced the production of ethanol as secondary metabolite and improved specific rates of growth, xylitol formation and substrate consumption. Fractionated supply of the feed medium at constant sugar concentration did not promote any increase on the productivity compared to the single batch cultivation.<br>A produção de xylitol por Candida parapsilosis foi investigada em regime de batelada alimentada, usando substratos açucarados de composição simples (xilose) ou composta (xilose e glicose). A presença de glicose no meio induziu a formação de etanol como metabólito secundário. A suplementação fracionada do meio de alimentação numa concentração fixa de açúcar não resultou em aumento da produtividade em relação àquela alcançada em batelada simples