Tree Species Shape Soil Bacterial Community Structure and Function in Temperate Deciduous Forests.

Amplicon-based analysis of 16S rRNA genes and transcripts was used to assess the effect of tree species composition on soil bacterial community structure and function in a temperate deciduous forest. Samples were collected from mono and mixed stands of Fagus sylvatica (beech), Carpinus betulus (hornbeam), Tilia sp. (lime), and Quercus sp. (oak) in spring, summer, and autumn. Soil bacterial community exhibited similar taxonomic composition at total (DNA-based) and potentially active community (RNA-based) level, with fewer taxa present at active community level. Members of Rhizobiales dominated at both total and active bacterial community level, followed by members of Acidobacteriales, Solibacterales, Rhodospirillales, and Xanthomonadales. Bacterial communities at total and active community level showed a significant positive correlation with tree species identity (mono stands) and to a lesser extent with tree species richness (mixed stands). Approximately 58 and 64% of indicator operational taxonomic units (OTUs) showed significant association with only one mono stand at total and active community level, respectively, indicating a strong impact of tree species on soil bacterial community composition. Soil C/N ratio, pH, and P content similarly exhibited a significant positive correlation with soil bacterial communities, which was attributed to direct and indirect effects of forest stands. Seasonality was the strongest driver of predicted metabolic functions related to C fixation and degradation, and N metabolism. Carbon and nitrogen metabolic processes were significantly abundant in spring, while C degradation gene abundances increased from summer to autumn, corresponding to increased litterfall and decomposition. The results revealed that in a spatially homogenous forest soil, tree species diversity and richness are dominant drivers of structure and composition in soil bacterial communities.

Biochemical profiles of two thermostable and organic solvent-tolerant esterases derived from a compost metagenome.

Owing to the functional versatility and potential applications in industry, interest in lipolytic enzymes tolerant to organic solvents is increasing. In this study, functional screening of a compost soil metagenome resulted in identification of two lipolytic genes, est1 and est2, encoding 270 and 389 amino acids, respectively. The two genes were heterologously expressed and characterized. Est1 and Est2 are thermostable enzymes with optimal enzyme activities at 80 and 70 °C, respectively. A second-order rotatable design, which allows establishing the relationship between multiple variables with the obtained responses, was used to explore the combined effects of temperature and pH on esterase stability. The response curve indicated that Est1, and particularly Est2, retained high stability within a broad range of temperature and pH values. Furthermore, the effects of organic solvents on Est1 and Est2 activities and stabilities were assessed. Notably, Est2 activity was significantly enhanced (two- to tenfold) in the presence of ethanol, methanol, isopropanol, and 1-propanol over a concentration range between 6 and 30% (v/v). For the short-term stability (2 h of incubation), Est2 exhibited high tolerance against 60% (v/v) of ethanol, methanol, isopropanol, DMSO, and acetone, while Est1 activity resisted these solvents only at lower concentrations (below 30%, v/v). Est2 also displayed high stability towards some water-immiscible organic solvents, such as ethyl acetate, diethyl ether, and toluene. With respect to long-term stability, Est2 retained most of its activity after 26 days of incubation in the presence of 30% (v/v) ethanol, methanol, isopropanol, DMSO, or acetone. All of these features indicate that Est1 and Est2 possess application potential.

A novel, versatile family IV carboxylesterase exhibits high stability and activity in a broad pH spectrum.

OBJECTIVES: To investigate the properties of a novel metagenome-derived member of the hormone-sensitive lipase family of lipolytic enzymes. RESULTS: A forest soil metagenome-derived gene encoding an esterase (Est06) belonging to the hormone-sensitive lipase family of lipolytic enzymes was subcloned, heterologously expressed and characterized. Est06 is a polypeptide of 295 amino acids with a molecular mass of 31 kDa. The deduced protein sequence shares 61% similarity with a hypothetical protein from the marine symbiont Candidatus Entotheonella sp. TSY1. Purified Est06 exhibited high affinity for acyl esters with short-chain fatty acids, and showed optimum activity with p-nitrophenyl valerate (C5). Maximum enzymatic activity was at 50 °C and pH 7. Est06 exhibited high stability at moderate temperatures by retaining all of its catalytic activity below 30 °C over 13 days. Additionally, Est06 displayed high stability between pH 5 and 9. Esterase activity was not inhibited by metal ions or detergents, although organic solvents decreased activity. CONCLUSIONS: The combination of Est06 properties place it among novel biocatalysts that have potential for industrial use including low temperature applications.