Molecular potential for the biosynthesis of protease inhibitors in cyanobacteria of the genus Microcystis and toxicity evaluation

Abstract

Secondary metabolites produced by cyanobacteria (e.g., cyanotoxins) are ranked among the most dangerous substances found in the surface water, and used by humans. However, many cyanopeptides present promising function and biological activities for pharmaceutical purposes, including enzyme inhibitors, antimicrobial agents, appetite suppressants, antimalarials, immunosuppressives and anti-tumor, but they are still underexploited. The production of protease inhibitors by cyanobacteria have been widely reported to strains of the genus Microcystis. Proteases are involved in a variety of physiological processes in the human body, such as cell cycle progression, food digestion, angiogenesis, blood clotting, blood pressure regulation, antigen presentation, apoptosis, and inflammation. Although a growing number of studies on cyanopeptides are available, information on their respective biosynthetic pathways, molecular structures, physiological and ecological functions is still scarce. The Brazilian tropical climate contributes to the cyanobacterial growth and the diversity of the cyanobacteria in these conditions is remarkable. Thus, novel cyanopeptides as well as new structural variants may be found along with their respective biosynthetic pathways. The general aims of this study are: 1) to investigate the potential for the production of the protease inhibitors aeruginosins and cianopeptolins in Microcystis strains, which were isolated from different Brazilian water bodies, including the semiarid region, 2) to evaluate their potential for microcystin production, the most common cyanotoxin in aquatic environments. Genomic DNA will be extracted and used for PCR amplification of the aerA-aerB and mcnC-mcnE regions of aeruginosin and cyanopeptolin synthetases. The mcyE gene will be used for the molecular detection of the potential for microcystin production in these isolates. Amplicons will be sequenced and the sequences generated will be used to determine the evolutionary distances based on phylogenetic trees. The mcyE gene sequences may be used for the future construction of biochips for detecting the toxicological potential of cyanobacteria in specific aquatic environments, as well as the detection of aeruginosin and cyanopeptolin sequences may nominate candidate strains for further studies on cyanobacterial bioprospection.