ORIGINAL ARTICLE Bioremediation of hexavalent chromium-contaminated wastewater by Bacillus thuringiensis and Staphylococcus capitis isolated from tannery sediment Gopal Suresh 1,2 & Balamuralikrishnan Balasubramanian 3 & Nagaiya Ravichandran 1 & Balasubramanian Ramesh 4 & Hesam Kamyab 5 & Palanivel Velmurugan 6 & Ganesan Vijaiyan Siva 1 & Arumugam Veera Ravi 6 Received: 31 August 2020 /Revised: 14 December 2020 /Accepted: 29 December 2020 # The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2021 Abstract The widespread use of hexavalent chromium Cr(VI) in the leather industry causes substantial environmental problems when effluents are left untreated. Therefore, the present work attempts to assess the ability of Bacillus thuringiensis (V45) and Staphylococcus capitis (S21), isolated from tannery industry sediment, to detoxify Cr(VI) by reducing the oxidation state. Initially, the minimum tolerance of chromium by both bacteria was found up to 1000 μg/mL. V45 could tolerate Cr(VI) (520 μg/mL), and S21 could also tolerate hexavalent Cr(VI) (340 μg/mL). Similarly, both bacteria were able to tolerate other metals such as Hg 2+ (40 μg/mL), Cu 2+ (30 μg/mL), Ni 2+ (60 μg/mL), Zn 2+ (40 μg/mL), and Pb 2+ (30 μg/mL). V45 and S21 could decrease Cr(VI) at a primary concentration of 50 μg/mL up to 86.42% and 97.34%, respectively. In optimization exper- iments, the best temperature to decrease Cr(VI) was shown to be 35 °C with pH 7 for 96 h. The occurrence of Cu 2+ and Na + slightly increased during the decrease of hexavalent Cr(VI) by V45, while the isolate S21 exhibited the same effects with Cu 2+ , Mn 2+ , and Na + . The carboxylate and amino conjugates in the biomass are intricate in the bioreduction of Cr(VI), as confirmed by FTIR spectroscopy. In addition, SEM imagery revealed the accumulation of Cr(VI) around both types of bacterial cells. The occurrence of other elements was evident from SEM-EDS spectroscopy. This study demonstrated the ability of native bacterial populations (V45 and S21) in tannery sediment to reduce Cr(VI) compounds. Keywords Bioremediation . Chromium (VI) . Tannery . Sediment bacteria 1 Introduction Chromium contamination in soil and groundwater generally results from the expulsion of wastes containing chromium (VI) via wastewater from tanneries, which is due to its wide use in the leather industry for the stabilization of the leather. Similarly, chromium is used in the manufacture of alloys, wood preservation, metal plating, steel, and pigmentation [1]. Chromium is present in the ecosystem as Cr(VI) and Cr(III) in oxidation states with dissimilar toxicity and mobility Balamuralikrishnan Balasubramanian is equal contributor as first author * Gopal Suresh sureshmicrobes@gmail.com * Palanivel Velmurugan palanivelmurugan2008@gmail.com 1 Department of Biotechnology, University of Madras, Guindy Campus, Chennai 600025, India 2 Department of Microbiology, Sri Sankara Arts and Science College (Autonomous), Enathur, Kanchipuram, Tamil Nadu 631561, India 3 Department of Food Science and Biotechnology, College of Life Science, Sejong University, Seoul 05006, South Korea 4 Department of Biotechnology, Sri Sankara Arts and Science College (Autonomous), Enathur, Kanchipuram, Tamil Nadu 631561, India 5 Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jln sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia 6 Department of Biotechnology, Alagappa University, Science Campus, Karaikudi, Tamil Nadu 630002, India https://doi.org/10.1007/s13399-020-01259-y Biomass Conversion and Biorefinery (2021) 11:383–391 Published online: 8 January 2021 /