Efeitos fisiológicos, morfológicos, ultraestruturais e potencial biorremediador de cianobactérias cultivadas com o fornecimento supra-ótimo de manganês

Abstract

Although manganese (Mn) is an essential micronutrient, it is toxic at high concentrations. This element is also a pollutant from waste from industrial and mining activities. The toxic effects of Mn are well known in terrestrial plants, but poorly understood in aquatic communities, especially in cyanobacteria. The objectives of this work were to analyze the toxic effects of this element and to analyze the potential of removal of Mn from the culture medium by cyanobacteria, aiming its application in the bioremediation of the Mn of contaminated aquatic environments. Two strains were selected, due to the morphological distinction of the groups, being a unicellular, colonial strain (Microcystis novacekii - BA005); and a heterocyte filamentous (Nostoc paludosum - BA033). Here, the effects of exposure to Mn in the two strains of cyanobacteria (BA005 and BA033) were evaluated through physiological, morphological and ultrastructural analyzes. The concentrations of Mn of 7.0, 10.5, 15.7, 23.6 and 35.4 mg · L-1 for BA005 and 15.0, 22.5, 33.7, 50.6 and 76.0 mg · L-1 for BA033 were used for analysis. The effects of Mn were evaluated by the growth inhibition test (EC50), chlorophyll a content and quantification of Mn accumulation in cyanobacteria biomass after 96 h of exposure. BA005 was more sensitive to Mn than BA033, with EC50 from 16 mg · L-1 to BA005 and 39 mg · L-1 to BA033. In addition, 56% and 54% reduction in chlorophyll a content associated with ultrastructural changes were observed at concentrations of Mn greater than 23.6 mg · L-1 and 33.7 mg · L-1 for BA005 and BA033, respectively. Damage to the cell envelope layers (increase of the periplasmic space), appearance of intrathylakoidal spaces and polyphosphate granules, as well as increase in the number of carboxy-enzymes were observed at high concentrations of Mn. Although the BA033 strain showed to be more resistant to the metal, surviving in higher concentrations, BA005 showed to be more efficient in the removal of the metal, achieving a removal of approximately 100% in the concentration 10.5 mg · L-1 Mn. Together, our results demonstrate the importance of toxicological studies for a better understanding of the effects of Mn on cyanobacteria strains, as well as on the bioreactor potential of Mn by cyanobacteria.