Biodiversity of Nitrate-Reducing Microbes in Grassland Soils by Massive Cultivation and Genomics (acronym: BE-Cult)

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The project BE-Cult adresses the biodiversity of nitrate ammonifying (syn. dissimilatory nitrate reducing to ammonium, DNRA) bacteria in soils of less and intensively managed grasslands of the Biodiversity Exploratories (BEs) at all grassland VIPs (very intensively studied plots). The relevance for keeping nitrogen (N) through DNRA bacteria in the soil has been long-time not much appreciated and their quantitive contribution to relase of nitrous oxide from soils has not been investigated. Thus, a lot information is available about biodiversity and eco-physiology of denitrifiers, which use also nitrate as electron acceptor in soil. The consequence of this history is that but not very much is known about the ecophysiology and significance of DNRA bacteria in terrestrial N cycling. In contrast to DNRA bacteria, dentrifiers produce N gases from nitrate and thus facilitate N loss in soils, whereas DNRA bacteria form ammonium that remains in soil and is a major plant nutrient. Both bacterial groups form the greenhouse gas nitrous oxide and thus contribute to global warming. The main aim of BE-Cult is to assess the impact of land use intensities on this important group N cycling soil microbes. By a high throughput cultivation approach (including MALDI TOF MS for rapid strain identification, and various physiological tests to group isolates) over 10,000 nitrate reducing isolates will be charcterized and clustered according to phylogeny and nitrate physiology. From this strain collection, 100 isolates will be selected and draft genomes will be gained. Based on genome information, new primers for functional gene markers will be developed to quantify these isolates in soil DNA extracts from VIPs and together with partners their relevance (i.e their activity compared to dentrifiers) will be assesed by targeted analyses of meta-transcriptomes. Finally, the revealed data will be used in multivariate analyses of functional gene abundances, physiological traits, and as well abiotic and biotic site parameters to explain the distribution patterns of DNRA bacteria in soils and to define their ecological niches.