Interaction between Thermotolerant Coliforms and Rhizobacteria in Soil Fertilized with Treated Domestic Wastewater

Abstract

ABSTRACT Studies on the survival of pathogenic microorganisms in the soil after use of wastewater for fertilization of agricultural crops report the effects of moisture, pH, organic matter, and soil temperature on microorganisms. There are few studies that assess the survival of these microorganisms in the rhizosphere of plants fertilized with wastewater. Thus, the aim of this study was to quantify the number of fecal coliforms and rhizobacteria (fluorescent Pseudomonas spp., Bacillus spp,) in the rhizosphere of winter and summer crops fertilized with wastewater. In the experiment, we used 20 plots, and each plot occupied an area of 200 m2. The treatments used in the winter crop consisted of uncultivated plots and single crops of wheat, triticale, black bean, and intercropped black bean/wheat. In the summer season, we used uncultivated plots and single crops of corn, sunflower, bean, and intercropped bean/corn. The experiment was conducted in a randomized block design with five treatments and four replications. Soil samples from the rhizosphere for microbiological analyses were collected at the flowering stage of the crops at a depth of 0.00-0.20 m. Plants stimulated fluorescent Pseudomonas spp. and Bacillus spp. in the rhizosphere, with average scores of 7.9 and 6.9 log CFU g-1 of dry soil, respectively, whereas in bare soil, these scores were 6.7 and 5.8 log CFU g-1 of dry soil for these rhizobacteria groups. However, this stimulating effect was not seen for fecal coliforms, which had an average score of 31.7 × 103 MPN g-1 of dry soil in the uncultivated area and 20.0 × 103 MPN g-1 of dry soil in crop areas. Overall, the numbers of rhizobacteria colonies in the rhizosphere soil under intercropping were higher than those observed in the rhizosphere soils of single winter and summer crops. Therefore, the presence of plants enhances the development of rhizobacteria and changes the balance among the species of microorganisms in the soil microbial community fertilized with wastewater.