EPS-Producing Bacteria Promote Aggregation in Soil Preventing the Leaching Loss of Nutrient

Leaching loss of nutrients from the agricultural field is a major concern in areas receiving excessive rainfall. The water-soluble nutrients are therefore lost due to leaching and runoff water. This leads to excessive dependence on chemical fertilizers. In this regard, the role of indigenous exopolysaccharide (EPS) producing bacteria in stabilizing the nutrient-holding capacity is far greater than conceived. The sub-Himalayan terai region, located at Cwa zone (monsoon type with dry winter, Köppen's classification) in India, which receives heavy rainfall (> 3000 mm), is a suitable location to study the role of such bacteria. A culture-dependent analysis of EPS-producing bacteria showed their comparatively lower abundance throughout the year. The EPS-associated bacterial microenvironment on vermiculite particles under aerobic and anaerobic conditions was visualized using a Confocal Laser Scanning Microscope (CLSM). The cells of EPS producers were found distributed within the EPS matrix, pushing each other away, showing a higher organic matter secretion (EPS) per unit of the bacterial cells. Since EPS has adhesive properties, the indigenous EPS-producing bacteria were amended to the soil, and the formation of macroaggregates was analyzed. Two in-house EPS-producing bacteria were used to monitor if they can reduce the leaching loss of nutrients. In vitro, assays on nutrient-holding capacity by soil-column-flow-through revealed that these bacteria-treated soil retained more nutrients. Till now, there were no reports on the role of the genus Serratia in improving the nutrient-holding capacity. For the first time, we have shown that using such soil-dwelling genera can improve the formation of stable aggregates and prevent nutrient loss.