Functional Diversity of Soil Microbial Communities in Environments Shaped by Anthropogenic Activities

Title: Bacillus strains isolated from agroforestry systems in the ama-zon promote the açaí palm seedlings growth when inoculated as a consortium
Authors: Josinete Torres Garcias; Rosiane do Socorro dos Reis de Sousa; Suania Maria do Nascimento Sousa; Lucimar Di Paula dos Santos Madeira; Allana Laís Alves Lima; Jackeline Rosseti Mateus; Joyce Kelly R. da Silva; Lucy Seldin; Hervé Louis Ghislain Rogez; Joana Montezano Marques
Affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará, Belém, Pará, Brasil
Abstract: The present work tested the hypothesis that açaí palm planted in agroforestry systems can recruit plant growth-promoting rhizobacteria (PGPR) to its rhizosphere. For this purpose, rhizospheric soil samples were collected in an Agroforest System (AFS) area for PGPR screening. CFU counts of the soil samples were 3.5 x 106 CFU/g, with no statistically significant differences between plants (p<0.05). Regarding PGPR characteristics, of 44 isolated strains, 18% produced siderophores, 9% mineralized organic phosphate, 15% solubilized inorganic phosphate, 7% produced IAA and an-timicrobial substances. Strains AP4-03, AP1-33 and AP2-36, were affiliated with the genus Bacillus sp. and produced of indole-3-acetic acid (IAA) at 1.45, 1.35 and 2.02 µg/mL, respectively. Fur-thermore, these strains were able to inhibit the growth of the fungus Pestalotiopsis by 69%, 67% and 71%, respectively. Regarding the antifungal activity of bacterial extracts, inhibition zones of 23mm (AP-03), 20mm (AP-33) and 18mm (AP-36), with 96% and 92% inhibition at 50 mg/mL (AP4 -03 and AP1-33) and 100% inhibition at 45 mg/mL (AP2-36) were observed. Considering seedling ger-mination, açaí palms inoculated with strain AP1-33 statistically differed from the controls in terms of root length and hypocotyl length. Furthermore, treatments inoculated with strain AP2-36 or all strains in consortium differed when only the hypocotyl length was compared to the control. PGPR strains were able to improve the initial development of açaí plants.

Title: Nodules of Medicago spp. host a diverse community of rhizobial species in natural ecosystems
Authors: Andrei Stefan; Jannick Van Cauwenberghe; Craita Maria Rosu; Catalina Stedel; Crystal Chan; Ellen L. Simms; Catalina Iticescu; Daniela Tsikou; Emmanouil Flemetakis; Rodica Catalina Efrose
Affiliation: Department of Biotechnology, Agricultural University of Athens, 75 Iera Odos Str., 11855 Athens, Greece
Abstract: Biological nitrogen fixation of rhizobia-colonized legumes can reduce the dependence on synthetic nitrogen fertilizers in crop fields. The identification and molecular characterization of locally-adapted rhizobia may lead to the discovery of economically important strains with applications in sustainable agriculture. We sampled rhizobia from root nodules of three Medicago species found in diverse ecosystems in Eastern Romania. An initial phenotypic screening ensured that only rhizobial species were retained for molecular characterization, and 16S rDNA sequencing clustered the isolates into four distinct groups corresponding to Sinorhizobium meliloti, Sinorhizobium medicae, Rhizobium leguminosarum and Mesorhizobium sp. The chromosomal genes (atpD, glnII, recA) and nifH phylogenies showed congruent topologies, while the nodA phylogeny grouped the Mesorhizobium sp. isolates into the R. leguminosarum cluster. Medicago sativa was the most sampled plant species and only S. meliloti and R. leguminosarum were found in its nodules, while Medicago falcata nodules hosted only S. meliloti and Mesorhizobium sp. Medicago lupulina was the only plant species that hosted all four identified rhizobial groups and the only one that hosted S. medicae. A comparative analysis of Medicago-associated rhizobia from other studies revealed that differences in 16S rDNA sequence type composition were influenced by Medicago species identity, but not by geographic region.

Title: Engineering Synthetic Microbial Communities: Diversity and Applications in Soil for Plant Resilience
Authors: Arneeb Tariq; Shengzhi Guo; Fozia Farhat; Xihui Shen
Affiliation: State Key Laboratory for Crop Stress Resistance and High-Efficiency Production, Shaanxi Key Laboratory of Agricultural and Environmental Microbiology, College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, P. R. China
Abstract: Plants host a complex but taxonomically assembled set of microbes in their natural environment which confer several benefits to the host plant including stress resilience, nutrient acquisition leading to more yield and productivity. To understand and simplify the intricate interactions among these microbes, an innovative approach Synthetic Microbial Community (SynCom) is practiced, involves intentional co-culturing of multiple microbial taxa under well-defined conditions mimicking the natural microbiomes. SynComs holds promising solutions to the issues confronted by modern agriculture stemming from climate change, limited resources, and land degradation. This review explores the potential of SynComs to enhance plant growth, development, and disease resistance in agricultural settings. We have summarized the role of SynComs in improving soil health by degrading the soil toxins and increasing the availability of essential micro and macro nutrients, biocontrol, and enhancing plant stress resistance. Furthermore, the current methodologies for formulating SynComs and their practical applications in agriculture are discussed. Despite the promising potential, the effectiveness of beneficial microbes in field applications has been inconsistent. There is a huge information gap, and much work remains to be done to understand the engineering involved in the complex ecological and metabolic networks that govern plant-microbe interactions. These efforts are crucial for advancing green technologies in agriculture.