IDENTIFICATION AND CHARACTERIZATION OF 2-MIB-PRODUCING CYANOBACTERIA IN FACHB

Odor problems in freshwater caused by 2-methylisoborneol (2-MIB) have received much attention in China recently. The odorous 2-MIB in freshwater is known to be mainly produced by a group of filamentous cyanobacteria which cause offensive taste and odor in drinking water and fish catch. From the detection of MIB synthase gene and GC/MS analyses, 24 strains of 2-MIB-producing cyanobacteria were detected in Freshwater Algae Culture Collection at the Institute of Hydrobiology (FACHB-collection), National Aquatic Biological Resource Center, the largest microalgal culture collection in China. These strains were re-identified as Planktothricoides raciborskii (Wołoszyńska) Suda & Watanabe, Aerosakkonema funiforme Thu & Watanabe, Pseudanabaena cinerea Tuji & Niiyama, Oscillatoria lutea var. contorta Baker et Bold, Microcoleus sp., Desertifilum tharense Dadheech & Krienitz and Sodalinema sp. by morphological descriptions and molecular characteristics based on the 16S rRNA gene, respectively. Most 2-MIB-producing strains of Planktothrix in FACHB-collection should be re-identified as P. raciborskii or A. funiforme. This was the first report of 2-MIB-producing filamentous cyanobacteria of Aerosakkonema, Desertifilum and Sodalinema in the world, and was also the first report of 2-MIB-producing Microcoleus in China. The phylogenetic analyses base on 16S rRNA gene indicated that 2-MIB-producing strains in FACHB-collection were placed on seven separated clades, which reflected true taxonomic relationships. The genera Planktothricoides, Aerosakkonema, Pseudanabaena, Microcoleus, Desertifilum and Sodalinema formed six monophyletic clades in 16S rDNA tree; however, O. lutea var. contorta was closely related to some strains of Oscillatoria, Phormidium and Kamptonema. The phylogenetic analyses based on mic gene indicated that 2-MIB-producing cyanobacteria strains formed five clades with high support values. 2-MIB-producing P. raciborskii and A. funiforme were clustered into Clade I in mic tree. Two 2-MIB-producing Microcoleus strains were placed on Clade Ⅱ and Ⅲ, respectively. All 2-MIB-producing Pseudanabaena strains were clustered into Clade Ⅳ. Phylogenetic topology of some 2-MIB-producing strains in mic tree were incongruent with the topology in 16S rDNA tree. Cell quota of 2-MIB produced by these strains may vary in a wide range, varying from 6—2549 fg/cell. Cell quota of 2-MIB varied considerably among species, such as P. raciborskii > A. funiforme > P. cinerea. The results provide important experimental materials and basic data on morphological, molecular, ecological and 2-MIB-producing characteristics of filamentous cyanobacteria, and contribute to understanding ecophysiological characteristics 2-MIB-producing cyanobacteria.