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Mont-Saint-Aignan, France

Lebrun J.D.,IRSTEA | Lebrun J.D.,AgriTerr Unit | Lebrun J.D.,French National Institute for Agricultural Research | Demont-Caulet N.,French National Institute for Agricultural Research | And 6 more authors.
Environmental Science and Pollution Research | Year: 2016

The present study investigates the effect of metals on the secretion of enzymes from12 fungal strains maintained in liquid cultures. Hydrolases (acid phosphatase, β-glucosidase, β-galactosidase, and N-acetyl-β-glucosaminidase) and ligninolytic oxidoreductases (laccase, Mn, and lignin peroxidases) activities, as well as biomass production, were measured in culture fluids from fungi exposed to Cu or Cd. Our results showed that all fungi secreted most of the selected hydrolases and that about 50 % of them produced a partial oxidative system in the absence of metals. Then, exposure of fungi to metals led to the decrease in biomass production. At the enzymatic level, Cu and Cd modified the secretion profiles of soil fungi. The response of hydrolases to metals was contrasted and complex and depended on metal, enzyme, and fungal strain considered. By contrast, the metals always stimulated the activity of ligninolytic oxidoreductases in fungal strains. In some of them, oxidoreductases were specifically produced following metal exposure. Fungal oxidoreductases provide a more generic response than hydrolases, constituting thus a physiological basis for their use as biomarkers of metal exposure in soils. © 2015, Springer-Verlag Berlin Heidelberg.

Bressan M.,AgriTerr Unit | Trinsoutrot Gattin I.,AgriTerr Unit | Desaire S.,AgriTerr Unit | Castel L.,AgriTerr Unit | And 2 more authors.
Applied Soil Ecology | Year: 2015

Soil microorganisms play key roles in ecosystem functioning. Finding tools to accurately measure, quantify and understand this component of soil is crucial to establish relevant indicators of the state of soil. This study proposes an optimized methodology using flow cytometry (FCM) for the quantification of bacteria in soil. This rapid and reproducible methodology was validated in two steps: (a) the recovery of spiked cells from sterilized soil matrix backgrounds and (b) the determination of the total number of bacteria from silty native soils (grassland and crop field). The ratio of counted SYBR Green-stained cells versus expected values amounted to 0.83 on average by FCM, compared to 0.64 by plate counts. We used this FCM method to compare bacterial abundance measured in four types of crop management systems: organic, integrated with (TRC) or without tillage (RTRC) and conventional. The FCM count ranged from 3.91×108 to 5.69×108cellsg-1 soil for crop field and was 6.69×108cellsg-1 soil for grassland. Similarly, two other frequently used descriptors of the bacterial community (quantification of the 16S rRNA gene by real-time PCR and total culturable heterotrophic bacteria by plate count analysis) were analyzed for all soils and compared with the FCM data. FCM counts were relevant enough to report significant differences between the four crop management systems. Higher bacterial counts were observed in conventional and integrated RTRC systems in comparison with organic and integrated TRC. The same tendency was observed when considering 16S rRNA gene abundance. As expected, a slight but significant correlation was observed between FCM counts and 16S rRNA gene quantification when considering all soil samples. No difference between crop management systems was noticed if we considered only colony forming unit (CFU) count. A calculated ratio between culturable and total bacterial counts (CFU/FCM) suggests some differences in the culturable proportion according to soil management.In the context of evaluating the state of soil, our FCM method offers a quick and simple assessment of total bacterial abundance in numerous samples. Combined with other biological indicators, FCM contributes to understanding soil bacterial biomass and could represent a useful complement in a larger panel of indicators to evaluate and detect changes in the structure of the soil microbial community. © 2015 Elsevier B.V.

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