title: Molecular basis and phylogenetic implications of deoxycylindrospermopsin biosynthesis in the cyanobacterium Raphidiopsis curvata.
abstract: New insights into the distribution and biochemistry of the cyanotoxin cylindrospermopsin (CYN) have been provided by the recent determination of its biosynthesis gene cluster (cyr) in several cyanobacterial species. Raphidiopsis curvata CHAB1150 isolated from China was analyzed for CYN analogues. Only 7-deoxy-CYN was detected in the cell extracts. The cyr gene cluster of R. curvata CHAB1150 was sequenced, and the cyr genes of this strain were found to have extremely high similarities (96% to 100%) to those from other nostocalean species. These species include Cylindrospermopsis raciborskii AWT205, Aphanizomenon sp. strain 10E6, and Aphanizomenon ovalisporum ILC-146. Insertion mutation was identified within the cyrI gene, and transcripts of cyrI and another functional gene cyrJ were detected in R. curvata CHAB1150. General congruence between the phylogenetic trees based on both cyr and 16S rrn was displayed. Neutral evolution was found on the whole sequences of the cyr genes, and 0 to 89 negative selected codons were detected in each gene. Therefore, the function of CyrI is to catalyze the oxygenation of 7-deoxy-CYN in CYN biosynthesis. The transcripts of the mutated cyrI gene may result from polycistronic transcription. The high conservation of the cyr genes may be ascribed to purifying selection and horizontal gene transfer.
authors.affiliation: Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, People’s Republic of China.
authors.forename: Yongguang
authors.initials: Y
authors.lastname: Jiang
authors.forename: Peng
authors.initials: P
authors.lastname: Xiao
authors.forename: Gongliang
authors.initials: G
authors.lastname: Yu
authors.forename: Tomoharu
authors.initials: T
authors.lastname: Sano
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Pan
authors.forename: Renhui
authors.initials: R
authors.lastname: Li
mesh_terms: D000470:Alkaloids / Q000096:biosynthesis*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002681:China; D000458:Cyanobacteria / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D000087522:Cyanobacteria Toxins; D004269:DNA, Bacterial / Q000032:analysis / Q000302:isolation & purification; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D000470:Alkaloids; D001426:Bacterial Proteins; D000087522:Cyanobacteria Toxins; D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; C430287:deoxy-cylindrospermopsin