Insights into the diversity of grassland soil bacterial communities associated with four contrasting Köppen climatic zones of India

Aims@#This study investigates the community structure and diversity of terrestrial soil bacterial communities thriving in four contrasting Köppen climatic zones of India using high-throughput sequencing.@*Methodology and results@#Soil samples were collected for metagenomic DNA isolation and PCR amplification using primers targeting the 16S rRNA gene region. Amplicons were subjected to Oxford nanopore sequencing and data analysis. Bacterial species diversity, evenness and richness were highest in a humid sub-tropical climatic zone (HSCZ). Firmicutes were the most abundant phylum in the tropical wet climatic zone (TWCZ), arid climatic zone (ACZ) and humid sub-tropical climatic zone (HSCZ), while Proteobacteria in the mountain climatic zone (MCZ). The predominance of class Alphaproteobacteria, Actinobacteria with genera Bradyrhizobium, Chthoniobacter and Mycobacterium, was observed in MCZ in contrast to class Bacilli with genera Bacillus and Paenibacillus in the rest of the zones. OTU abundance was positively correlated with moisture, TOC (total organic carbon), K, MAP (mean annual precipitation) and negatively correlated with pH, Ca, N, B, Fe, P, Mg and MAT (mean annual temperature). A significant correlation was only observed with Fe against Shannon diversity (H’) in multiple regression analysis. @*Conclusion, significance and impact of study@#The multidirectional relationship between soil, its microbiota and climate is crucial in modulating bacterial community diversity and its survival in terrestrial ecosystems that significantly contribute to ecosystem function. This work mapped the occurrence and distribution of terrestrial soil bacterial communities in contrasting climatic zones for the first time, enabling us to assess the effect of climate in the mentioned Köppen climatic zones.

Diversidad microbiana en estudios de fertilización mineral de larga duración en caña de azúcar / Microbial diversity in studies of long-term mineral fertilization studies in sugarcane

RESUMEN Las comunidades microbianas son esenciales para la productividad de los agroecosistemas. En caña de azúcar, el uso de fertilizantes nitrogenados, como práctica de manejo común, mantiene los niveles de la productividad del cultivo e influye en la diversificación del microbioma, ocasionando cambios en la diversidad de los microorganismos involucrados en el ciclo del nitrógeno (N). El objetivo de este estudio consistió en analizar la influencia de diferentes regímenes de fertilización nitrogenada sobre la estructura y la composición de la comunidad microbiana rizosférica, en un experimento de larga duración. Esta investigación permitirá establecer un régimen de fertilización más preciso. Se demostró que no existen diferencias significativas en la composición y en la estructura de la comunidad bacteriana, al usar diferentes niveles de fertilización nitrogenada en caña de azúcar. Los Phylum Acidobacteria, Firmicutes y Mortierellomycota fueron los más relacionados con las dosis de nitrógeno recomendadas, para obtener altos rendimientos agrícolas, bajo las condiciones de Cuba; sin embargo, existieron variaciones en cuanto a composición y abundancias relativas de los Phylum de la micobiota respecto a las dosis de nitrógeno aplicadas, con predominio de los Phylum Ascomycota y Basidiomycota. Fueron detectadas diferencias significativas, a nivel de género y familia, debido a la presencia de organismos probióticos en las parcelas no tratadas.

ABSTRACT Microbial communities are essential for the productivity of agroecosystems. In sugarcane, using nitrogen fertilizers as a common management practice to keep crop productivity influences the diversification of the microbiome, causing changes in the diversity of microorganisms involved in the nitrogen (N) cycle. In a long-term experiment, this study aimed to analyze the influence of different nitrogen fertilization levels on the structure and composition of the rhizospheric microbial community. This research will help to establish a more precise fertilization regime. There were no significant differences in the composition and structure of the bacterial community when using different levels of nitrogen fertilization in sugarcane. Significant differences were detected at the genus and family level due to the presence of probiotic organisms in the untreated plots. The Phylum Acidobacteria, Firmicutes, and Mortierellomycota were the most related to the recommended nitrogen doses to obtain high agricultural yields under the conditions of Cuba. However, there were variations in composition and relative abundances of the Phylum of the mycobiota concerning the doses of nitrogen applied with a predominance of the Phylum Ascomycota and Basidiomycota. Significant differences were detected at the genus and family level due to the presence of probiotic organisms in the untreated plots.

Selection of biosurfactan/bioemulsifier-producing bacteria from hydrocarbon-contaminated soil

Petroleum-derived hydrocarbons are among the most persistent soil contaminants, and some hydrocarbon-degrading microorganisms can produce biosurfactants to increase bioavailability and degradation. The aim of this work was to identify biosurfactant-producing bacterial strains isolated from hydrocarbon-contaminated sites, and to evaluate their biosurfactant properties. The drop-collapse method and minimal agar added with a layer of combustoleo were used for screening, and positive strains were grown in liquid medium, and surface tension and emulsification index were determined in cell-free supernantant and cell suspension. A total of 324 bacterial strains were tested, and 17 were positive for the drop-collapse and hydrocarbon-layer agar methods. Most of the strains were Pseudomonas, except for three strains (Acinetobacter, Bacillus, Rhodococcus). Surface tension was similar in cell-free and cell suspension measurements, with values in the range of 58 to 26 (mN/m), and all formed stable emulsions with motor oil (76-93 percent E24). Considering the variety of molecular structures among microbial biosurfactants, they have different chemical properties that can be exploited commercially, for applications as diverse as bioremediation or degradable detergents.