Análises de transcrição gênica em cianobactérias, como ferramenta para estudar suas relações com o ambiente

Abstract

Cyanobacteria represent an important group among phytoplanktonic organisms. They are very diverse and can be mainly found in highly eutrophic environments. One of the main problems related to cyanobacteria is the production of toxins that can be harmful for both of humans beings and aquatic animals. Additionally, they are capable of producing a variety of secondary metabolites with function is still unknown. Microcystins are hepatoxins produced by many species of cyanobacteria and they are the main toxins found in toxic blooms. They can cause liver hemorrhages and, in the long run, it seems that they can induce tumors appearance. However not all cyanobacteria species are toxic and this characteristic is found in the genome of toxics strains by the presence of the mcy genes. Very little is known about the real function of the cyanotoxins and about whether their production is controlled by environmental factors. Some researches indicated pH, light, nutrients and temperature as possible reasons for the variation of toxin production observed in the environment. The purpose of this work was to evaluate in laboratory experiments and in the environment, the effect of environmental factors in the expression of the mcyD gene and others cyanopeptides. Furthermore, measures of others genes, linked to nitrogen metabolism (ntcA), phosphorous uptake (pstS), iron metabolism (furN) and oxidative stress (perM), were performed in the field in an attempt to verify factors that could affect cyanopeptides’ production in cyanobacteria. We also investigated the toxic and non-toxic fractions of natural cyanobacteria populations and the presence of some cyanopeptides, by mean of molecular methods. In the laboratory experiments, two cyanobacteria strains were submitted to different levels of phosphorus and nitrogen limitation. In the environmental studies, eigth samples from an eutrophic reservoir, Pampulha, and twelve samples of the an oligotrophic reservoir, Volta Grande, were collected. We observed that environmental factors had an effect on the gene expression of several genes tested and on microcystin production. Under stress conditions, we observed higher production of two cyanopeptides, microcystin in the lab and cyanopeptolin in the field. The results obtained in this study seem to indicate that the stress caused by changes in environmental parameters can induce the production of certain cyanopeptides and this could somehow help in the process of acclimatization and survival of cyanobacteria to factors triggered by stress. It is possible that this study will contribute to a better understanding about which factors are associated with the regulation of microcystin production and the potential function of the cyanopeptides for the cell. Moreover, this research may give support to futures studies and procedures dealing with the control of cyanobacteria populations in water bodies.