Acta Scientiarum http://periodicos.uem.br/ojs ISSN on-line: 1807-8664 Doi: 10.4025/actascitechnol.v43i1.49854 BIOTECHNOLOGY Acta Scientiarum. Technology, v. 43, e49854, 2021 Enterococci and Bacilli from surface water: assessment of their resistance to copper and antibiotics Luciana Furlaneto Maia * , Gabriela Batista Gomes Bravo, Alex Kiyomassa Watanabe, Nayara de Oliveira Batista and Márcia Cristina Furlaneto Universidade Tecnológica Federal do Paraná, Av. Sete de Setembro, 3165, 80240-001, Curitiba, Paraná, Brazil. *Author for correspondence. E-mail: lumaia_2007@hotmail.com ABSTRACT. Heavy metal-resistant bacteria can be efficient bioremediators of metals and might provide an alternative method for metal removal in contaminated environments. The present study aims to isolate bacteria from the aquatic environment and evaluate their potential tolerance to copper metal, aiming at bioremediation processes. Also, compare co-resistance to heavy metal and antibiotics. The morphology of isolates was observed, and sequence analysis (16S ribosomal DNA) revealed that isolated strains were closely related to species belonging to the genera Enterococcus and Bacillus. Bacterial isolates were resistant to CuSO4, with a minimum inhibitory concentration of 0.78 mg ml -1 . Enterococcus lactis was resistant to a combination of copper and tetracycline. The other tested isolates were sensitive to the tested antimicrobials. The metal removal ability of these isolates was assayed using atomic absorption spectroscopy, and the strains 27, 23, and E. lactis were best at removing heavy metals, at 87.7%. Enterococcus casseliflavus EC55 was 62%, followed by Bacillus aerius (18.4%), E. casseliflavus EC70 (10%) and Bacillus licheniformis (10%). Based on our findings, Enterococcus sp and Bacillus sp. have potential applications in enhanced remediation of contaminated environments. Keywords: heavy metal-resistant; Enterococcus sp; Bacillus sp; CuSO4. Received on September 4, 2019. Accepted on March 24, 2019. Introduction It is known that the increased use of metals and chemicals in the process industries has resulted in the generation of large amounts of effluents containing toxic heavy metals and these effluents can accumulate in the environment, due to their non-degradable nature (Gautam, Gautam, Banerjee, Chattopadhyaya, & Pandey, 2016). Toxic metals can accumulate along the food chain, causing chronic toxicity to the aquatic environment and in humans (Pugazhendhi, Ranganathan, & Kaliannan, 2018). Several microorganisms that live in these environments adopt different mechanisms to adapt to these heavy metal and antibiotics stresses. This occurs because some mechanisms for heavy metal resistance function in a similar way of those for resistance to antibiotics. It is very important to elucidate the bacterial resistance to both in detail for further understanding the bacterial cross-resistance and its ecological risk (Zhou et al., 2015). On the other hand, this co-resistance can facilitate the bioremediation of heavy metal by the microorganism (Selvi et al., 2012). Many living bacteria have been reported to transform toxic contaminants into their less toxic forms (Karthik et al., 2017). Bioremediation processes have attracted much attention as part of the search for new, economically viable technologies for the removal of toxic metals from the environment. Bioremediation is advantageous because conventional methods (e.g., chemical precipitation, membrane separation, ion exchange, reverse osmosis, chemical oxidation, electrochemical treatment, and adsorption) are relatively costly and eco-friendly (Peng et al., 2010; Weng et al., 2014; Gautam et al., 2016; Karthik et al., 2017). However, the first step for a bioremediation process project, it is suggested to determine the microorganisms existing in contaminated areas, since these native microorganisms, in addition to tolerating metals, are also adapted to the environmental conditions of temperature, humidity and pH (Muñoz-Silva, Olivera-Gonzales, Torres, & Tamariz-Angeles, 2019).