In this paper the ecophysiological effects of microcystins on bacteria and its possible mechanism were studied. The main results are as follows:
1.The growth and biochemical response of E.coli and B. subtilis to MC-RR were studied. The results showed that the growth and cell viability of bacteria were inhibited for a short period compared with that of the control when exposed to MC-RR. E.coli and B. subtilis only showed growth inhibition at the initial growth phase when cells were treated with MC-RR. Indeed the normal rate of growth was gradually re-established and the growth curves of the toxin-treated and untreated bacteria became parallel. The contents of protein and soluble sugar in cells increased compared with that of the control at the beginning of MC-RR exposure and then gradually decreased. The permeabilising ability of MC-RR under different concentrations to the cell outer membrane of E. coli and B. subtilis was demonstrated by a rapid and sustained reduction in the OD675 values of lysozyme-treated cells. The extravasations of protein and soluble sugar increased with the increment of the treated-concentration of MC-RR and the prolonged of the treated-time.
2.E.coli and B. subtilis was undertaken to determine the effect of MC-RR on microbes. With high concentrations MC-RR exposure, the results showed that the ROS level and TBARS contents of E.coli were obviously increased after 1 h exposure to MC-RR. At the same time, the activities of antioxidant enzymes including SOD and CAT as well as GR activity and GSH contents in bacterial cells were also increased when exposed to microcystin –RR for 1 h, subsequently decreased. For B. subtilis, the activity of antioxidant enzymes including SOD and CAT was significantly increased than that of the control when exposed to 5 or 10 mg/L MC-RR for 1 h. The contents of TBARS and GSH as well as GR activity were obviously increased only when exposed to 10 mg/L MC-RR. For the time-effect of MC-RR on B. subtilis, the activities of antioxidant enzymes including SOD and CAT as well as GR activity and TBARS, GSH content in B. subtilis were first significantly increased and than subsequently decreased.
3.Two strains denitrifying bacteria and Organic phosphorus bacteria were isolated to further study the effect of MC-RR on the population of functional bacteria. From the morphological characteristics and results of 16S rDNA sequence analysis, the denitrifying bacteria were identified as Bacillus gibsonii and Oceanobacillus iheyensis, the organic phosphorus bacteria were identified as Serratia marcescens. The growth and denitrification function of denitrifying bacteria were prolonged by MC-RR. It showed a time- and dose-effect. The decrease of Nitrate and the increase of nitrite were both inhibited as a result of the growth and NR activity inhibition. Indeed with the toxin-treated time increased, the normal rate of growth was gradually re-established. The effect of MC-RR on organic phosphorus bacteria was similar to that on denitrifying bacteria. The enzyme activity of ACP and ALP were lower than that of the control and finally the content of phosphate in liquid medium decreased with the exposure of MC-RR.