Growth and Cellular Responses of Toxigenic Microcystis to Chloramphenicol-Stress at Various Environmentally-Relevant Nitrogen Levels.

This study explored nitrogen (N)-dependent interaction between Microcystis and chloramphenicol (CAP) along 20 day-test. Results showed that 5 mg/L N largely alleviated inhibitory effects of CAP on Microcystis growth, while 50 and 0.5 mg/L N exacerbated growth-inhibition by CAP especially in early (before day 8) and mid–late stage, respectively. At each N level, CAP-induced antioxidant defense and cell damage extents were negatively correlated to growth state in each stage, and CAP-biodegradation coincided with Microcystis growth and glutathione synthesis dynamics, implying that antioxidant defense, cell damage and CAP-removal closely linked to N-dependent Microcystis growth under CAP-stress. Microcystin (MC)-production and -release under CAP-stress were also N-dependent. Although Microcystis growth was greatly-inhibited by prolonged CAP-stress at 0.5 mg/L N, delayed CAP-loss and high MC-release at 0.5 mg/L N should be emphasized during Microcystis-dominated cyanobacterial blooms (MCBs) and CAP co-occurrence. This study had great implication in risk assessment for MCBs–CAP co-occurrence in different waters. [ABSTRACT FROM AUTHOR]