CHEMICAL ENGINEERING TRANSACTIONS VOL. 74, 2019 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Sauro Pierucci, Jiří Jaromír Klemeš, Laura Piazza Copyright © 2019, AIDIC Servizi S.r.l. ISBN 978-88-95608-71-6; ISSN 2283-9216 Isolation and Molecular Identification of Arsenic Resistant Microorganisms Coming from Xichu River, Gto. Mexico. Ulises E. Rodríguez a, * , Alma H. Serafín b , Maria C. Cano c , Norma L. Gutiérrez b , Aurelio Álvarez c a University of Guanajuato, Posgrado de Ciencias del Agua, División de Ingenierías, Guanajuato, Mexico. b University of Guanajuato, División de Ingenierías, Guanajuato, Mexico. c University of Guanajuato, División de Ciencias Naturales y Exactas, Guanajuato, Mexico. erodriguezcastrejon@gmail.com The arsenic is a toxic element for the human and other organisms´ health, it may affect the exploitation of water, the agriculture development and the sustainable rational use of soil, the result is reflected within the socioeconomic growth lag in the affected area. Arsenic is mobilized in the environment by a combination of several natural processes, such as weathering reactions, biological activities and volcanic emissions, as well as by a group of anthropogenic activities. Microorganisms interact with the arsenic through a different mechanism such as adsorption, redox, precipitation, etc. On the other hand, the rate of arsenic releasing in geochemical environments is controlled mainly by microorganisms. In the environment, the major arsenic transformations include microbial oxidation, reduction, methylation and demethylation, those reactions have an enormous impact in the arsenic behavior that depends on its redox state that exhibits differences in its mobility and toxicity. Normally, the arsenic resistance comes through the production of genes within operon ars, their location is usually plasmid or chromosomic. In this study, it was achieved the isolation of 11 strains from which 2 have been reported as an arsenic resistant in this work. The samples were collected from water, sediment and biofilm of Xichu River, which has been impacted by mining activity, exhibiting a high arsenic concentration (98 μg/l). All the strains were tested by several methods as arsenic resistance, colorimetric test for arsenate reduction, pDNA extraction as well as ars and aox genes amplification, which are the genes involved in arsenic transformation. It was obtained a great microbial diversity with different skills in arsenic transformation. One of the isolated strains Rodoccoccus gordoniae, did not show the presence of any gen but it was the most likely microorganisms to grow in the presence of arsenic. Almost all the microorganisms showed arsenic resistant until 20 mM of arsenite and arsenate. The main contribution of this study is the development of knowledge to understand much better the arsenic biogeochemistry, as well as the development of new bio-technologies for water treatment in rural communities impacted by mining activity. 1. Introduction Heavy metals in aquatic environments is increasing due to industrialization and unconcerned polluted process. Some metals are classified as toxic to human and living environment. They are of particular concern in the treatment of industrial wastewaters including arsenic (III) and (V), cadmium (III), chromium (III), etc (Srisorrachatr, 2017) Arsenic is a toxic element for humans and other living organisms. By contaminating natural sources of water, it affects their use, the development of sustainable agriculture and the sustainability of the rational use of soils, which is reflected in the lagging socio-economic growth of the affected region (Litter et al., 2009). The toxic effects of As are related to its chemical form and its oxidation state: its organic form is less toxic. On the other hand, in its inorganic form it occurs in two redox states: the reduced form, arsenite (III), and the oxidized form arsenate (V), both of which are toxic to most organisms. Arsenic is commonly found in natural waters in its dissolved form as oxyanions. As (V) is found in its H 3 AsO 4 form and its corresponding dissociation products (H 2 AsO - 4 , HAsO 4 2- and AsO 4 3- ). As (III) appears as H 3 AsO 3 and its corresponding dissociation products (H 4 AsO 3+ , H 2 AsO 3- , HAsO 3 2- and AsO 3 3- ), (Campos and Valenzuela., DOI: 10.3303/CET1974255 Paper Received: 11 June 2018; Revised: 8 September 2018; Accepted: 13 February 2019 Please cite this article as: Rodriguez U., Serafin A., Cano C., Gutierrez N., Alvarez A., 2019, Isolation and Molecular Identification of Arsenic Resistant Microorganisms Coming from Xichu River, Gto. Mexico., Chemical Engineering Transactions, 74, 1525-1530 DOI:10.3303/CET1974255 1525