Characteristics of a Microcystin-Degrading Bacterium under Alkaline Environmental Conditions

Kunihiro Okano,Motoo Utsumi,Zhenya Zhang,Brett A Neilan,Norio Sugiura,Hideaki Maseda,Kazuya Shimizu,Yukio Kawauchi

doi:10.1155/2009/954291

Abstract

The pH of the water associated with toxic blooms of cyanobacteria is typically in the alkaline range; however, previously only microcystin-degrading bacteria growing in neutral pH conditions have been isolated. Therefore, we sought to isolate and characterize an alkali-tolerant microcystin-degrading bacterium from a water bloom using microcystin-LR. Analysis of the 16S rRNA gene sequence revealed that the isolated bacterium belonged to the genus Sphingopyxis, and the strain was named C-1. Sphingopyxis sp. C-1 can grow; at pH 11.0; however, the optimum pH for growth was pH 7.0. The microcystin degradation activity of the bacterium was the greatest between pH 6.52 and pH 8.45 but was also detected at pH 10.0. The mlrA homolog encoding the microcystin-degrading enzyme in the C-1 strain was conserved. We concluded that alkali-tolerant microcystin-degrading bacterium played a key role in triggering the rapid degradation of microcystin, leading to the disappearance of toxic water blooms in aquatic environments.

Highlights

Toxic blooms of cyanobacteria frequently occur in eutrophic lakes, ponds, and reservoirs throughout the world [1,2,3,4,5,6,7]
Analysis of its 16S rRNA gene sequence revealed that the bacterium belonged to the genus Sphingopyxis, order Sphingomonadales of the α-proteobacteria (Figure 1)
A dynamic change in the pH of aquatic environments from neutral to alkaline is associated with the occurrence of the blooms of cyanobacteria in water bodies [3, 5,6,7]

Summary

Introduction

Toxic blooms of cyanobacteria frequently occur in eutrophic lakes, ponds, and reservoirs throughout the world [1,2,3,4,5,6,7]. It has been reported that up to 70% of these blooms are potentially toxic [8]. Cyanobacteria, such as Microcystis, Anabaena, Planktothrix (Oscillatoria), Nostoc, and Hapalosiphon species, produce a family of cyclic heptapeptide hepatotoxins called microcystins (MCs) [9, 10]. MCs inhibit protein serine/threonine phosphatases 1 and 2A and promote tumour growth [10,11,12,13]. An important concern is that chronic exposure to low concentrations of MCs in drinking water may promote tumour growth in the human liver [11, 14]. Drinking water supplies all over the world are regularly contaminated with MCs, posing a threat to public health. In 1996, more than 50 haemodialysis patients in Caruaru, Brazil, died because the water used for dialysis was contaminated with MCs [15, 16]

Methods

Results

Conclusion