Divergent responses of functional gene expression to various nutrient conditions during microcystin-LR biodegradation by Novosphingobium sp. THN1 strain

•Microcystin-LR biodegradation was investigated under various nutrient conditions.•At each condition degradation followed mlr gene expression up-regulation until 42h.•Degradation efficacy corresponded to mlr gene expression with phosphate and nitrate.•Expression of mlrA was coupled with that of mlrD under various nutrient conditions.•mlr expression may not be dominant factor for degradation efficiency with ammonium. To better understand the mechanisms for microcystin-LR (MCLR) biodegradation, the linkage between MCLR-biodegradation kinetics and functional gene expression dynamics was originally investigated with Novosphingobium sp. THN1 as inoculum under various nutrient conditions. Along biodegradation, mlrA gene expression, coupled with mlrD, presented similar trend but was regulated differentially among different conditions. Good positive correlation was observed between MCLR degraded and induction ratios of functional genes until 42h at respective condition. Compared to those under nutrient-free condition, the stimulated or decelerated biodegradation with dipotassium phosphate (DP) or ammonium chloride (AC) (both at 100mg L−1) was related to higher or lower up-regulation in mlr gene expression, suggesting that divergent mlr gene expression was one of the reasons for different effects of DP or AC on degradation. However, stimulated degradation with sodium nitrate (100mg L−1) might involve other mechanisms where mlr expression was not the decisive prerequisite to govern MCLR-biodegradation.