Production of exopolysaccharides by Bacillus spp. from hydrocarbon-contaminated soils in the Ecuadorian Amazonia

Abstract

The high degree of compaction of Ecuadorian Amazonian clay soils represents a serious limitation for bioremediation due to reduced oxygen availability. Microbial exopolysaccharides (EPS) improve soil particle aggregation and soil structure. In this context, this research evaluated the EPS-producing capacity of four native Bacillus isolates, by culturing them in a liquid basal medium modified with sucrose and sugarcane molasses as carbon sources and tryptone and yeast extract as nitrogen sources. EPS production was strongly influenced by both the isolate and the culture conditions. Sugarcane molasses significantly enhanced EPS synthesis compared to controls, with concentrations rising from 85–326 µg/mL to 243–662 µg/mL, the highest value being 661.9 µg/mL in one isolate. Yeast extract as a nitrogen source also promoted higher EPS production than controls, ranging from 69–501 µg/mL, with peak production of 501.2 µg/mL. Stress conditions further affected EPS output: across pH treatments, EPS ranged from 136–367 µg/mL, with optimal production near neutral pH, while moderate salinity stimulated EPS synthesis, increasing concentrations from 171–221 µg/mL in NaCl-free controls to 262–376 µg/mL at 0.7–1.1% NaCl. The most productive isolates were identified as Bacillus altitudinis, Bacillus licheniformis and Paenibacillus glycanilyticus; all of them have a potential biotechnological use in the improvement of the structure of hydrocarbon-contaminated soils that are bioremediated in the Ecuadorian Amazonia.