Bacteria from the endosphere and rhizosphere of Quercus spp. use mainly cell wall-associated enzymes to decompose organic matter

Abstract

Due to the ability of soil bacteria to solubilize minerals, fix N2 and mobilize nutrients entrapped in the organic matter, their role in nutrient turnover and plant fitness is of high relevance in forest ecosystems. Although several authors have already studied the organic matter decomposing enzymes produced by soil and plant root-interacting bacteria, most of the works did not account for the activity of cell wall-attached enzymes. Therefore, the enzyme deployment strategy of three bacterial collections (genera Luteibacter, Pseudomonas and Arthrobacter) associated with Quercus spp. roots was investigated by exploring both cell-bound and freely-released hydrolytic enzymes. We also studied the potential of these bacterial collections to produce enzymes involved in the transformation of plant and fungal biomass. Remarkably, the cell-associated enzymes accounted for the vast majority of the total activity detected among Luteibacter strains, suggesting that they could have developed a strategy to maintain the decomposition products in their vicinity, and therefore to reduce the diffusional losses of the products. The spectrum of the enzymes synthesized and the titres of activity were diverse among the three bacterial genera. While cellulolytic and hemicellulolytic enzymes were rather common among Luteibacter and Pseudomonas strains and less detected in Arthrobacter collection, the activity of lipase was widespread among all the tested strains. Our results indicate that a large fraction of the extracellular enzymatic activity is due to cell wall-attached enzymes for some bacteria, and that Quercus spp. root bacteria could contribute at different levels to carbon (C), phosphorus (P) and nitrogen (N) cycles.

Molecular diversity and hydrolytic enzymes production abilities of soil bacteria

“…Of 72 isolates, strain ALA1, ALA3, ALA4, and ALA5 exhibited maximum production of extracellular amylase, cellulase, and inulinase. In accordance with the previous reports ( Singh and Kumari, 2016 , Hussain et al, 2017 , Guttikonda et al, 2017 , Dida, 2018 , Manzum and Al Mamun, 2018 , Ramapriya et al, 2018 , Lasa et al, 2019 ) who demonstrated soil bacteria as ideal producers of enzymes, our findings revealed comparatively higher production of amylase, cellulase, and inulinase from Bacillus spp. and Glutamicibacter sp.…”

Characterization of the belowground microbial community in a poplar-assisted bioremediation strategy for restoring a multi-contaminated soil

“…This means that the planting layout of the poplars (0.5 × 2m) was effective in ensuring that their root development positively stimulated the overall microbial community in each planted plot. The positive "rhizosphere effect" has been reported by other authors [26,27] and was presumably due to the root surface releasing several organic compounds into the adjacent soil. Roots release low-molecular-weight exudates (e.g.…”

Characterization of the Belowground Microbial Community in a Poplar-Phytoremediation Strategy of a Multi-Contaminated Soil

“…This means that the planting layout of the poplars (0.5 × 2 m) was effective in ensuring that their root development positively stimulated the overall microbial community in each planted plot. The positive "rhizosphere effect" has been reported by several authors (Thomas and Cébron, 2016;Lasa et al, 2019b;Schneijderberg et al, 2020) and was presumably due to the root surface releasing several organic compounds into the adjacent soil. Roots release low-molecular-weight exudates (e.g., sugars, polysaccharides, amino acids, aromatic acids, aliphatic acids, fatty acids, sterols, phenolic compounds, enzymes, proteins, plant growth regulators, and secondary metabolites) which attract soil microorganisms into the rhizosphere, where they multiply by several orders of magnitude (Badri et al, 2009).…”

“…Extraction of environmental RNA and DNA (eDNA) from each soil sample (Rhizo, Bulk and Control) was carried out using the RNA Power Soil Total RNA Isolation Kit and the DNA Elution Accessory kit (Qiagen), following the manufacturer’s recommendations. In order to evaluate the putative active bacteria in Rhizosphere and Bulk Soil, the same soil samples were used for RNA extraction; the latter was extracted as reported above and ds-cDNA synthesized in accordance with ( Lasa et al, 2019b ). Both eDNA and ds-cDNA were used as templates for MiSeq Illumina sequencing of the hypervariable V4–V5 region of the 16S rRNA gene, using the U519F and U926R primers ( Baker et al, 2003 ).…”