Abstract
Environmental contamination by heavy metals (HMs) poses several indirect risks to human health, including the co-spreading of genetic traits conferring resistance to both HMs and antibiotics among micro-organisms. Microbial antibiotic resistance (AR) acquisition is enhanced at sites anthropogenically polluted by HMs, as well as in remote systems naturally enriched in HMs, such as hydrothermal vents in the deep sea. However, to date, the possible role of hydrothermal vents at shallower water depths as hot spots of microbial AR gain and spreading has not been tested, despite the higher potential risks associated with the closer vicinity of such ecosystems to coasts and human activities. In this work, we collected waters and sediments at the Panarea shallow-water hydrothermal vents, testing the presence of culturable marine bacteria and their sensitivity to antibiotics and HMs. All of the bacterial isolates showed resistance to at least one antibiotic and one HM and, most notably, 80% of them displayed multi-AR on average to 12 (min 8, max 15) different antibiotics, as well as multi-HM tolerance. We show that our isolates displayed high similarity (≥99%) to common marine bacteria, affiliating with Actinobacteria, Gammaproteobacteria, Alphaproteobacteria and Firmicutes, and all displayed wide growth ranges for temperature and salinity during in vitro physiological tests. Notably, the analysis of the genomes available in public databases for their closest relatives highlighted the lack of genes for AR, posing new questions on the origin of multi-AR acquisition in this peculiar HM-rich environment. Overall, our results point out that shallow-water hydrothermal vents may contribute to enhance AR acquisition and spreading among common marine bacteria in coastal areas, highlighting this as a focus for future research.
Highlights
Microbial antibiotic resistance (AR) is spreading critically worldwide, threatening human and animal health [1,2]
The environmental settings found during our sampling period (September 2019) at the different sites of the Panarea hydrothermal system investigated in this study are reported in
In this study, we obtained five bacterial strains isolated from the Bottaro
Summary
Microbial antibiotic resistance (AR) is spreading critically worldwide, threatening human and animal health [1,2]. No information is available to date on the occurrence and patterns of microbial AR in shallow-water hydrothermal vents, high concentrations of HMs were found in these ecosystems [25,27] and occur worldwide near coastal areas, being more closely linked to human health and activities than deep-sea hydrothermal vents [28,29,30] To start filling this gap, for the present work, we collected waters and sediments at the Panarea shallow-water hydrothermal vents in the Mediterranean Sea [27,31,32], assessing the diversity and testing the sensitivity of culturable marine bacteria to different classes of antibiotics. As a proof of concept, we completed this study by investigating HM concentrations in the collected sediments and concurrent HMR of the identified antibiotic-resistant strains
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