Studies on phosphate solubilizing bacteria from two lakes in central southern Ontario

Abstract

It has been well documented that phosphorus pollution has been one of the most significant factors inhibiting aquatic health on Lake Simcoe. However, reports on the impacts of microbial contribution to phosphorus levels are sparse. Phosphate solubilizing bacteria (PSB), are a group of bacteria that are known to release inorganic phosphate from sediments into a bioavailable form of phosphorus under specific conditions and are the focus of the present study. Sediment samples were collected once monthly from June-September 2017 from three nearshore locations along the northwestern shore of Lake Simcoe and compared to three nearshore locations along Sparrow Lake, ON. The phosphate solubilizing bacteria were isolated from the sediment, and the abundances between each lake were compared to see if anthropogenic influence was a factor on their abundance and distribution. After the bacterial isolates were counted, they were subjected to a series of laboratory tests in order to find out which of the isolates were the most efficient ones at utilizing inorganic phosphate. This test was first completed on Pikovskaya’s agar plates, and then the isolates that had the best results were tested again in Pikovskaya’s broth. The ten isolates that utilized the most inorganic phosphate were further classified on their abilities to grow at various temperatures, pH levels, and inorganic phosphate concentrations. Results indicated that there were significant differences on the abundance of PSBs based on their lake of origin (three-factor ANOVA, p<0.05). However, the higher abundance was observed in Sparrow Lake, which did not agree with the hypothesis that PSBs would be more abundant in areas that had high nutrient concentrations. Results from a laboratory screening test showed that the isolate incubation period had a significant impact on how efficient the isolates were at utilizing inorganic phosphate on the Pikovskaya’s agar plates (repeated measures ANOVA, p<0.05). They also showed that some of the isolates were significantly better at utilizing the inorganic phosphate in the broth than others (1-factor ANOVA, p<0.05), and that of the ten isolates that were characterized, only three were significantly different from each other (discriminant function analysis, p<0.001). The phosphate solubilizing bacteria were found to be most abundant and grew the best when they originated from areas that had water total phosphorus concentrations of less than 2mg/L. Thus, indicating that this group of microorganisms may not be useful as indicators of phosphorus pollution.