University of São Paulo, Center for Nuclear Energy in Agriculture, Avenida Centenário 303, 13400-970 Piracicaba, SP, Brazil.
Toxicon. 2010 Apr 1;55(4):846-54. doi: 10.1016/j.toxicon.2009.12.001. Epub 2009 Dec 7.
A nostocalean nitrogen-fixing cyanobacterium isolated from an eutrophic freshwater reservoir located in Piracicaba, São Paulo, Brazil, was evaluated for the production of hepatotoxic cyclic heptapeptides, microcystins. Morphologically this new cyanobacterium strain appears closest to Nostoc, however, in the phylogenetic analysis of 16S rRNA gene it falls into a highly stable cluster distantly only related to the typical Nostoc cluster. Extracts of Nostoc sp. CENA88 cultured cells, investigated using ELISA assay, gave positive results and the microcystin profile revealed by ESI-Q-TOF/MS/MS analysis confirmed the production of [Dha(7)]MCYST-YR. Further, Nostoc sp. CENA88 genomic DNA was analyzed by PCR for sequences of mcyD, mcyE and mcyG genes of microcystin synthetase (mcy) cluster. The result revealed the presence of mcyD, mcyE and mcyG genes with similarities to those from mcy of Nostoc sp. strains 152 and IO-102-I and other cyanobacterial genera. The phylogenetic tree based on concatenated McyG, McyD and McyE amino acids clustered the sequences according to cyanobacterial genera, with exception of the Nostoc sp. CENA88 sequence, which was placed in a clade distantly related from other Nostoc strains, as previously observed also in the 16S rRNA phylogenetic analysis. The present study describes for the first time a Brazilian Nostoc microcystin producer and also the occurrence of demethyl MCYST-YR variant in this genus. The sequenced Nostoc genes involved in the microcystin synthesis can contribute to a better understanding of the toxigenicity and evolution of this cyanotoxin.
从巴西皮拉西卡巴的一个富营养化淡水水库中分离到一株固氮蓝藻，对其产生肝毒性环七肽微囊藻毒素的能力进行了评估。从形态上看，这种新的蓝藻菌株与念珠藻最为相似，但在 16S rRNA 基因的系统发育分析中，它属于一个与典型念珠藻关系较远的高度稳定聚类。使用 ELISA 检测培养细胞的 Nostoc sp. CENA88 提取物，结果呈阳性，ESI-Q-TOF/MS/MS 分析显示的微囊藻毒素图谱证实了[Dha(7)]MCYST-YR 的产生。此外，还通过 PCR 对 Nostoc sp. CENA88 基因组 DNA 进行了微囊藻毒素合成酶(mcy)基因簇的 mcyD、mcyE 和 mcyG 基因序列分析。结果表明，存在 mcyD、mcyE 和 mcyG 基因，与 Nostoc sp. 152 和 IO-102-I 等蓝藻属菌株以及其他蓝藻属的 mcy 基因具有相似性。基于串联的 McyG、McyD 和 McyE 氨基酸构建的系统发育树根据蓝藻属对序列进行聚类，除 Nostoc sp. CENA88 序列外，该序列与其他 Nostoc 菌株的亲缘关系较远，这与 16S rRNA 系统发育分析结果一致。本研究首次描述了巴西念珠藻产生微囊藻毒素的情况，也首次在该属中发现了去甲基 MCYST-YR 变体。参与微囊藻毒素合成的已测序 Nostoc 基因有助于更好地理解这种蓝藻毒素的毒性和进化。
