RESUMO
NtcA is a transcription factor that has been found in a diverse range of cyanobacteria. This nitrogen-controlled factor was focused on as a key component in the yet-to-be-deciphered regulatory network controlling microcystin production. Adaptor-mediated PCR was utilized to isolate the ntcA gene from Microcystis aeruginosa PCC 7806. This gene was cloned, and the recombinant (His-tagged) protein was overexpressed and purified for use in mobility shift assays to analyze NtcA binding to putative sites identified in the microcystin mcyA/D promoter region. Autoregulation of NtcA in M. aeruginosa was shown via NtcA binding in the upstream ntcA promoter region. The observation of binding of NtcA to the mcyA/D promoter region has direct relevance for the regulation of microcystin biosynthesis, as transcription of the mcyABCDEFGHIJ gene cluster appears to be under direct control of nitrogen.
Assuntos
Proteínas de Bactérias , Proteínas de Ligação a DNA , Regulação Bacteriana da Expressão Gênica , Microcistinas/biossíntese , Microcystis/metabolismo , Regiões Promotoras Genéticas/fisiologia , Fatores de Transcrição , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Sítios de Ligação , Clonagem Molecular , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Ensaio de Desvio de Mobilidade Eletroforética , Microcystis/genética , Nitrogênio/metabolismo , Reação em Cadeia da Polimerase , Regiões Promotoras Genéticas/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Over the last 10 years, we have witnessed major advances in our understanding of natural product biosynthesis, including the genetic basis for toxin production by numerous groups of cyanobacteria. Cyanobacteria produce an unparalleled array of bioactive secondary metabolites, including alkaloids, polyketides and non-ribosomal peptides, some of which are potent toxins. This review addresses the molecular genetics underlying the production of hepatotoxins, microcystin and nodularin in fresh and brackish water. These toxins pose a serious threat to human health and their occurrence in water supplies is increasing, because of the prevalence of toxic algal blooms worldwide. Toxin biosynthesis gene-cluster-associated transposition and the natural transformability of certain species suggest a broader distribution of toxic cyanobacterial taxa. The information gained from the discovery of these toxin biosynthetic pathways has enabled the genetic screening of various environments for drinking-water quality management. Understanding the role of cyanotoxins in the producing microorganisms and the environmental regulation of their biosynthesis genes may also suggest the means of controlling toxic-bloom events.
