Mixing regimes shape microbial community composition, nutrient regimes, and plant growth attributes in Jeevamrit:...

Jeevamrit, a microbial inoculant widely used in zero-budget natural farming (ZBNF) that relies on local farm-based resources to enhance overall biological health of soil, is reported for inconsistent crop yield enhancements. This is mainly due to variability in its preparation methods, e.g., mixing intensity, incubation regimes, and quality of ingredients used. Hence, the current study aimed to decipher the effect of mixing intensity (extent of oxygenation) on microbial community composition, nutrient transformation, and plant growth attributes of Jeevamrit, using a combined metagenomics-culturomics approach. Frequent mixing (Constant/Intermediate) enhanced nutrient solubilization (Fe, Zn, Cu, Mn) with higher total N and dissolved organic carbon, while less mixing (Anoxic/No-mix) led to accumulation of soluble Fe and NH₄⁺-N with higher microbial diversity. Mixing-driven differential enrichment of taxa were noted, i.e., constant mixing (CM) dominated by Acinetobacter (~ 40%), Comamonas, Pseudomonas, and Lysinibacillus, linked to oxidative C/N cycling and metal dissolution. Whereas, anoxic (AO) favored Clostridium sensu stricto, Lactobacillales, Enterococcus, and Enterobacterales (> 60%), correlating to fermentative metabolism-driven reductive elemental cycling. Co-occurrence network analysis identified Acinetobacter, Pseudomonas, Comamonas, Trichococcus, and Stenotrophomonas as hubs, indicating keystone functions in structuring metabolic interactions. The metagenome-recovered MAGs belonged to Acinetobacter sp., Clostridium saccharobutylicum, Trichococcus flocculiformis, and Enterococcus gallinarum with potential to participate in multiple nutrient cycling. Cultivable members of Shigella, Rhodococcus, and Bacillus spp. showed high IAA production (135-145 µg mL⁻¹), NH₃ release (~ 0.12 µg mL⁻¹), and K and P solubilization (~ 55.2 µg mL⁻¹). We hypothesize that oxygenation drives the Jeevamrit's microbial guild assembly, where mixing intensity modulates oxido-reductive metabolism and nutrient mobilization efficiency, indicating the requirement for standardization of formulation aligned to soil-specific conditions.