Rhizosheath drought responsiveness is variety-specific and a key component of belowground plant adaptation.

Biophysicochemical rhizosheath properties play a vital role in plant drought adaptation. However, their integration into the framework of plant drought response is hampered by incomplete mechanistic understanding of their drought responsiveness and unknown linkage to intraspecific plant-soil drought reactions. Thirty-eight Zea mays varieties were grown under well-watered and drought conditions to assess the drought responsiveness of rhizosheath properties, such as soil aggregation, rhizosheath mass, net-rhizodeposition, and soil organic carbon distribution. Additionally, explanatory traits, including functional plant trait adaptations and changes in soil enzyme activities, were measured. Drought restricted soil structure formation in the rhizosheath and shifted plant-carbon from litter-derived organic matter in macroaggregates to microbially processed compounds in microaggregates. Variety-specific functional trait modifications determined variations in rhizosheath drought responsiveness. Drought responses of the plant-soil system ranged among varieties from maintaining plant-microbial interactions in the rhizosheath through accumulation of rhizodeposits, to preserving rhizosheath soil structure while increasing soil exploration through enhanced root elongation. Drought-induced alterations at the root-soil interface may hold crucial implications for ecosystem resilience in a changing climate. Our findings highlight that rhizosheath soil properties are an intrinsic component of plant drought response, emphasizing the need for a holistic concept of plant-soil systems in future research on plant drought adaptation.

Unique architecture of microbial snottites from a methane driven biofilm revealed by confocal microscopy.

Microbial biofilms occur in many shapes and different dimensions. In natural and semi-artificial caves they are forming pendulous structures of 10 cm and more. In this study a methane driven microbial community of a former medicinal spring was investigated. The habitat was completely covered by massive biofilms and snottites with a wobbly, gelatinous appearance. By using fluorescence techniques in combination with confocal laser scanning microscopy the architecture of these so far unknown snottites was examined. The imaging approaches applied comprised reflection of geogenic and cellular origin, possible autofluorescence, nucleic acid staining for bacterial cells, protein staining for bacteria and extracellular fine structures, calcofluor white for ß 1 → 3, ß 1 → 4 polysaccharide staining for possible fungi as well as lectin staining for the extracellular biofilm matrix glycoconjugates. The results showed a highly complex, intricate structure with voluminous, globular, and tube-like glycoconjugates of different dimensions and densities. In addition, filamentous bacteria seem to provide additional strength to the snottites. After screening with all commercially available lectins, by means of fluorescence lectin barcoding and subsequent fluorescence lectin binding analysis, the AAL, PNA, LEA, and Ban lectins identified α-Fuc, ß-Gal, ß-GlcNAc, and α-Man with α-Fuc as a major component. Examination of the outer boundary with fluorescent beads revealed a potential outer layer which could not be stained by any of the fluorescent probes applied. Finally, suggestions are made to further elucidate the characteristics of these unusual microbial biofilms in form of snottites. RESEARCH HIGHLIGHTS: The gelatinous snottites revealed at the microscale a highly complex structure not seen before. The extracellular matrix of the snottite biofilm was identified as clusters of different shape and density. The matrix of snottites was examined by taking advantage of 78 fluorescently-labeled lectins. The extracellular matrix glycoconjugates of snottites identified comprised: α-Fuc, ß-Gal, ß-GlcNAc, and α-Man. Probing the snottite outer surface indicated an additional unknown stratum.

Microbial methane formation in deep aquifers of a coal-bearing sedimentary basin, Germany.

Coal-bearing sediments are major reservoirs of organic matter potentially available for methanogenic subsurface microbial communities. In this study the specific microbial community inside lignite-bearing sedimentary basin in Germany and its contribution to methanogenic hydrocarbon degradation processes was investigated. The stable isotope signature of methane measured in groundwater and coal-rich sediment samples indicated methanogenic activity. Analysis of 16S rRNA gene sequences showed the presence of methanogenic Archaea, predominantly belonging to the orders Methanosarcinales and Methanomicrobiales, capable of acetoclastic or hydrogenotrophic methanogenesis. Furthermore, we identified fermenting, sulfate-, nitrate-, and metal-reducing, or acetogenic Bacteria clustering within the phyla Proteobacteria, complemented by members of the classes Actinobacteria, and Clostridia. The indigenous microbial communities found in the groundwater as well as in the coal-rich sediments are able to degrade coal-derived organic components and to produce methane as the final product. Lignite-bearing sediments may be an important nutrient and energy source influencing larger compartments via groundwater transport.

Phylogenetic and functional diversity within toluene-degrading, sulphate-reducing consortia enriched from a contaminated aquifer.

Three toluene-degrading microbial consortia were enriched under sulphate-reducing conditions from different zones of a benzene, toluene, ethylbenzene and xylenes (BTEX) plume of two connected contaminated aquifers. Two cultures were obtained from a weakly contaminated zone of the lower aquifer, while one culture originated from the highly contaminated upper aquifer. We hypothesised that the different habitat characteristics are reflected by distinct degrader populations. Degradation of toluene with concomitant production of sulphide was demonstrated in laboratory microcosms and the enrichment cultures were phylogenetically characterised. The benzylsuccinate synthase alpha-subunit (bssA) marker gene, encoding the enzyme initiating anaerobic toluene degradation, was targeted to characterise the catabolic diversity within the enrichment cultures. It was shown that the hydrogeochemical parameters in the different zones of the plume determined the microbial composition of the enrichment cultures. Both enrichment cultures from the weakly contaminated zone were of a very similar composition, dominated by Deltaproteobacteria with the Desulfobulbaceae (a Desulfopila-related phylotype) as key players. Two different bssA sequence types were found, which were both affiliated to genes from sulphate-reducing Deltaproteobacteria. In contrast, the enrichment culture from the highly contaminated zone was dominated by Clostridia with a Desulfosporosinus-related phylotype as presumed key player. A distinct bssA sequence type with high similarity to other recently detected sequences from clostridial toluene degraders was dominant in this culture. This work contributes to our understanding of the niche partitioning between degrader populations in distinct compartments of BTEX-contaminated aquifers.