Responses of microbial communities to dosing with the algicide thiazolidinedione derivative TD49 in a mesocosm experiment

Abstract

To clarify the effects of the algicide thiazolidinedione derivative 49 (TD49) on a microbial community, including the targeted harmful alga Heterocapsa circularisquama, we conducted exposure experiments (control, blank, 0.2, 0.4, 0.6, and 1.0 &micro M) with TD49 in mesocosm enclosures (1300 L). The algicidal effects on the target alga depended on the concentration of TD49. The algicide TD49 concentration also decreased significantly with the increase of exposure time (R2= 0.99, P<0.001), suggesting that the toxic effect of algicide may have not occurred or may be lower because it was rapidly reduced in the natural water. Following the addition of TD49, heterotrophic bacteria (HB) and heterotrophic nano-flagellates (HNFs) grew well in all treatments. In particular, the abundance of HNFs lagged behind the increase in HB, which is occurred the 24 h time lag in 0.2-0.4 &micro M TD49 (r= 0.53, F= 7.03 p<0.05) and 48 h time lag in 0.6-1.0 &micro M TD49(r= 0.55, F= 5.99, p<0.05). This implies a primary cue for strong top-down effects on microbial communities within TD dose-dependent, suggesting that the degradation of planktonic organisms, including target algae, led to high HB concentrations, and the predator HNF had accelerated within the time lag. Total ciliates remained relatively low in abundance in TD49 treatments compared to control and blank groups, whereas aloricate ciliate abundance gradually increased at the end .0 &micro M) with TD49 in mesocosm enclosures (1300 L). The algicidal effects on the target alga depended on the concentration of TD49. The algicide TD49 concentration also decreased significantly with the increase of exposure time (R2= 0.99, P<0.001), suggesting that the toxic effect of algicide may have not occurred or may be lower because it was rapidly reduced in the natural water. Following the addition of TD49, heterotrophic bacteria (HB) and heterotrophic nano-flagellates (HNFs) grew well in all treatments. In particular, the abundance of HNFs lagged behind the increase in HB, which is occurred the 24 h time lag in 0.2-0.4 &micro M TD49 (r= 0.53, F= 7.03 p<0.05) and 48 h time lag in 0.6-1.0 &micro M TD49(r= 0.55, F= 5.99, p<0.05). This implies a primary cue for strong top-down effects on microbial communities within TD dose-dependent, suggesting that the degradation of planktonic organisms, including target algae, led to high HB concentrations, and the predator HNF had accelerated within the time lag. Total ciliates remained relatively low in abundance in TD49 treatments compared to control and blank groups, whereas aloricate ciliate abundance gradually increased at the end