[Effects of different iron concentrations on the growths of a unicellular strain and a colonial strain of Microcystis aeruginosa].

We investigated the growth, photosynthetic efficiency, siderophore production and iron accumulation of two strains of M. aeruginosa, a unicellular strain M. aeruginosa PCC7806 and a colonial strain M. aeruginosa XW01, under iron-limited and iron-replete conditions. The identities of ITS and fur gene sequences of two strains were 95% and 98% respectively.That implied the two strains should be close relatives. Results showed the growths of two strains were severely inhibited under an iron-limited condition. The unicellular strain died in 6 days,whereas the colonial strain could maintain a weak growth in 10 days under the iron-limited condition. PSII maximum light energy transformation (Fv/Fm) of the colonial strain and the unicellular strain were 0.182 +/- 0.014 and 0.160 +/- 0.017, respectively. The colonial strain displayed a higher photosynthetic oxygen evolution than the unicellular strain. Two strains could produce siderophores, which were hydroxamate type. The colonial strain produced more siderophores than unicellular strain under the iron-limited condition.Iron contents of two strains were less than 1/3 cultured in the iron-limited condition than in iron-replete condition, but no obvious difference appeared between the two strains. Our result demonstrated that the colonial strain have a stronger endurance than unicellular strain under the iron-limited condition. As two strains had almost same abilities of iron accumulation, the other physiological mechanisms in the unicellular strain should be more sensitive to lower iron level.

[Composition of Microcystis species of the cyanobacterial bloom in Xuanwu Lake of Nanjing].

The aim of the present study was to clarify the community composition of cyanobacterial bloom in Xuanwu Lake of Nanjing city. The Microcystis colonies in cyanobacterial blooms sampled from Xuanwu Lake during August 2005 and September 2006 were identified by morphological characteristics and internal transcribed spacer sequence (ITS). The results indicated that the bloom was composed mainly by Microcystis aeruginosa, M. novacekii and M. wesenbergii. The biomass percentage of them was 30%-45%, 35%-40% and 10%-15%, respectively. ITS of two dominant Microcystis strains were amplified by PCR and sequenced to identify their species. The analysis of ITS sequences and the ITS phylogenetic tree demonstrated that the two dominant species should be M. aeruginosa and M. novacekii. A microcystin-producing gene mcyB was detected to test toxic strain. A unique product of approximately 780 bp was amplified in two dominant strains. It indicated that both of them were of microcystin-producing genotype. High performance liquid chromatography (HPLC) analysis showed that the toxins in the native bloom biomass were mainly MC-LR and MC-RR.