For the first time a microcystin-degrading bacterium (NV-3 isolate) has been isolated and characterized from a NZ lake. Cyanobacterial blooms in New Zealand (NZ) waters contain microcystin (MC) hepatotoxins at concentrations which are a risk to animal and human health. Degradation of MCs by naturally occurring bacteria is an attractive bioremediation option for removing MCs from drinking and recreational water sources. The NV-3 isolate was identified by 16S rRNA sequence analysis and found to have 100% nucleotide sequence homology with the Sphingomonas MC-degrading bacterial strain MD-1 from Japan. The NV-3 isolate (concentration of ？CFU/mL) at 30°C degraded a mixture of [Dha7]MC-LR and MC-LR (concentration 25？μg/mL) at a maximum rate of 8.33？μg/mL/day. The intermediate by-products of [Dha7]MC-LR degradation were detected and similar to MC-LR degradation by-products. The presence of three genes (mlrA, mlrB, and mlrC), that encode three enzymes involved in the degradation of MC-LR, were identified in the NV-3 isolate. This study confirmed that degradation of [Dha7]MC-LR by the Sphingomonas isolate NV-3 occurred by a similar mechanism previously described for MC-LR by Sphingomonas strain MJ-PV (ACM-3962). This has important implications for potential bioremediation of toxic blooms containing a variety of MCs in NZ waters. 1. Introduction Toxic cyanobacterial blooms in eutrophic lakes, ponds, and reservoirs are a common occurrence around the world [1–3]. Cyanobacteria of the genera Microcystis, Anabaena, Nostoc, and Planktothrix produces a wide range of potent toxins, including a family of heptapeptide hepatotoxins, referred to as microcystins (MCs). Microcystins are the most frequently detected cyanobacterial toxins, which cause hepatotoxicity and tumor promotion in wild animals, livestock, and humans [2, 4, 5]. Epidemiological studies of primary liver cancer in China and the death of 56 patients during a dialysis treatment in Caruaru, Brazil triggered worldwide concern about toxicity of MCs [4, 5]. Approximately 75 variants of MCs have been identified and MC-L (leucine) R (arginine) is the most common variant of MC worldwide [1, 6–9]. Limited studies in New Zealand (NZ) have reported the occurrence of the [Dha7]MC-LR variant occurring with high frequency in NZ waters [3, 10, 11]. Microcystins are chemically stable over a wide range of temperature and pH, possibly as a result of their cyclic structure [12]. The toxins are also resistant to enzymatic hydrolysis by some general proteases, such as pepsin, trypsin, collagenase and chymotrypsin [13]. However,
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