Abstract
Bacterial extracellular polymeric substances (EPSs) present diverse properties of biotechnological interest, such as surface modification, metal adsorption and hydrophobic substances solubilization through surface tension reduction. Thus, there is a growing demand for new producing strains and structurally variable biomolecules with different properties. One approach for scanning this biodiversity consists of exploring environments under selective pressures. The aim of this study was to evaluate the composition of culturable heterotrophic bacterial communities from five different sites from a copper mine in the Amazon biome by an enrichment technique to obtain metal resistant bacteria (lead, arsenic, cadmium, copper and zinc) capable of producing EPSs. The bacterial densities at the sites varied from 2.42 × 103 to 1.34 × 108 NMP mL−1 and the 77 bacterial isolates obtained were classified in four divisions, β-Proteobacteria (16.88%), γ-Proteobacteria (7.29%), Firmicutes (61%) and Actinobacteria (12.98%). Bacillus, Alcaligenes, and Lysinibacillus were the most dominant among the 16 observed genera, but the relative frequency of each varied according to the sample and the metal used in the enrichment culture. 58% of the bacterial strains (45) could produce EPSs. From these, 33 strains showed emulsifying activity (E24), and 9 of them reached values higher than 49%. Only Actinomyces viscosus E3.Pb5 and Bacillus subtilis group E3.As2 reduced the medium surface tension to values lower than 35 mN m−1. It was possible to confirm the high presence of bacteria capable of producing EPSs with tensoactive properties in Amazon copper mines and the evolutionary pressure exerted by the heavy metals during enrichment. These molecules can be tested as an alternative for use in processes that involve the removal of metals, such as the bioremediation of contaminated environments.
Highlights
Metal mining has been crucial for human society since the Iron and Bronze Ages[3]
They can modify surfaces mediating the adhesion and de-adhesion interactions between the microbial cells and interfaces[11,12]. Considering these properties, extracellular polymeric substances (EPSs) have the potential to be employed as heavy metal removers and hydrophobic compound emulsifiers in remediation procedures, depending on their functional groups and on their tensoactives properties, whose effectivity can be measured by their surfactant and emulsifying activities (E24 index)
Total heterotrophic bacteria (THB) densities varied according to the mining site (Fig. 1)
Summary
Metal mining has been crucial for human society since the Iron and Bronze Ages[3]. But nowadays, mining faces challenges to efficiently recover metals from the low-grading ores, treat all the waste generated, and remediate the affected areas. The remediation of mining contaminated areas is a huge concern worldwide and remediating technologies based on microorganisms appear as a promising alternative for achieving treatment goals[4] Within this context, the aim of this study was to compare the bacterial diversity of five different sites in a copper mine located in the Amazon biome and to reveal differences in the communities regarding the density of cultivable heterotrophic metal-resistant and EPS producing bacteria. The aim of this study was to compare the bacterial diversity of five different sites in a copper mine located in the Amazon biome and to reveal differences in the communities regarding the density of cultivable heterotrophic metal-resistant and EPS producing bacteria This characterization is a step towards the discovery of substances with possible applications in biotechnological and bioremediation processes and an attempt to overcome the limitations that hinder the use of these molecules on a larger scale
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