Occurrence and Distribution of Bacteria in Non-Rhizospheric Soils of Rice Fields across Four Regions of Bangladesh

Non-rhizospheric soil refers to the bulk soil that lies outside the immediate influence of plant roots and their exudates, typically exhibiting lower microbial activity and reduced nutrient availability compared to the rhizosphere. This study investigates the diversity and characterization of bacterial communities in non-rhizospheric soils from rice fields across four districts of Bangladesh, including Dinajpur, Mymensingh, Netrokona, and Savar. Non-rhizospheric soil samples were collected, and bacteria were isolated using nutrient agar, enumerated as colony-forming units (CFU/g), and differentiated based on colony morphology. Bacterial loads varied significantly, with the highest count (1.04 × 10¹⁰ CFU/g) in Mymensingh and the lowest (1.64 × 10⁹ CFU/g) in Savar. Cultural, morphological, and biochemical analyses were performed on 18 distinct bacterial isolates, which were identified as Staphylococcus sp., Pseudomonas sp., Micrococcus sp. Bacillus sp., Alcaligenes sp. and Vibrio sp., among which Staphylococcus sp. was found to be the predominant isolate across the sites. Furthermore, molecular identification of the bacterial isolates was performed using 16S rRNA gene sequencing, which confirmed the species of the isolated bacteria. Biocontrol assays demonstrated the ability of Pseudomonas sp. to inhibit foodborne Staphylococcus sp. Antibiotic susceptibility test revealed multidrug resistance, with all isolates resistant to most antibiotics but uniformly sensitive to amikacin. This study highlights the non-rhizospheric soil of rice fields as a reservoir of diverse bacterial communities, with Staphylococcus sp. showing dominance and regional variation in bacterial abundance, underscoring the ecological importance of these microbial populations.