Potencial de biorremediação ao cromo por Exiguobacterium acetylicum isolada da macrófita Hydrocotyle ranunculoides

Abstract

Chromium (Cr) is one of the most common contaminants in aquatic systems due to its frequent use in metallurgical, electroplating and tanning industries. For human health, exposure to this metal can trigger genetic changes and diseases such as cancer. Bioremediation is an environmentally and economically viable process in which living organisms are used to reduce or remove contaminants from environment. Rhizoremediation is a bioremediation technique that becomes one of the most ecological and efficient methods for decontaminating soils and aquatic environments. However, success of this technique depends on the microorganisms being resistant and tolerant to metals and showing effectiveness in different environmental conditions. Rhizosphere microbial community can also vary according to plant species, nutritional status, age, stress, among others. Thus, it was sought to identify bioremediator bacteria existing in rhizosphere of macrophyte plants of the species Hydrocotyle ranunculoides present at Santa Bárbara stream, in the city of Pelotas-RS, capable of biosorbing chromium as well as knowing the optimal environmental conditions for remediation. The isolate called HR7 identified as Exiguobacterium acetylicum showed better viability and bioremoval among those selected, being analyzed under different conditions for Cr (III) removal such as: different pHs, chromium concentrations, temperatures and growth. The species was also tested for its ability to grow and remove Cr (VI) from medium. Thus, the isolate showed adaptability to the environmental variables under study, demonstrating optimal growth and removal at a concentration of 50 mg.L-1 of Cr (III), at pH from neutral to alkaline (between 7 and 8), at temperatures range between 35ºC and 40ºC and with ideal contact time with the metal in the range of 12 to 24 h. In the Cr (VI), the isolate showed excellent viability and metal removal rates of almost 100% at concentrations of 10, 25 and 50 mg.L-1. Thus, rhizoremediation constitutes an efficient technique for remediation of contaminated aquatic environments, and the bacterial species studied demonstrates to be a microorganism with great potential for further studies, aiming its application in bioremediation processes.