Advanced

Do heavy metals select for bacterial tolerance to antibiotics in soils?

Rabow, Sandra (2018) BION02 20181
Degree Projects in Biology
Abstract
Due to the public health threat that antibiotic resistance poses to humanity, there is increasing interest for understanding the mechanisms behind the development and transfer of antibiotic resistance genes (ARGs) in different environments. Soil is one of the largest and most diverse microbial habitats on earth and represents a vast terrestrial reservoir of organisms with tolerance to antibiotics. In addition to antibiotics, non-antibiotic compounds, such as heavy metals, have also been shown to co-select for antibiotic resistance in soils. This is of particular concern since unlike antibiotics, heavy metals persist in soils, more likely to accumulate and exert toxic effects on soil bacteria. In this study, samples with a wide range of... (More)
Due to the public health threat that antibiotic resistance poses to humanity, there is increasing interest for understanding the mechanisms behind the development and transfer of antibiotic resistance genes (ARGs) in different environments. Soil is one of the largest and most diverse microbial habitats on earth and represents a vast terrestrial reservoir of organisms with tolerance to antibiotics. In addition to antibiotics, non-antibiotic compounds, such as heavy metals, have also been shown to co-select for antibiotic resistance in soils. This is of particular concern since unlike antibiotics, heavy metals persist in soils, more likely to accumulate and exert toxic effects on soil bacteria. In this study, samples with a wide range of heavy metal concentrations were collected from coniferous forest soils surrounding the smelter Rönnskär in northern Sweden. First, using PLFA analysis and different methods for measuring process rates (thymidine incorporation, acetate-in-ergosterol, and CO2 production), it was shown that heavy metals from the smelter Rönnskär had a significant impact on microbial community composition, bacterial growth rates and overall microbial activity. Using a pollution induced community tolerance (PICT) approach, this study then provided strong, direct evidence that heavy metal pollution selected for bacterial tolerance to copper (Cu) at soil concentrations exceeding c. 200 mg kg-1 and co-selected for tolerance to the antibiotic tetracycline. In a short term microcosm experiment, Cu exposure induced Cu-tolerance. This, however, did not translate into an induced co-tolerance to tetracycline. The difference between co-tolerance in the microcosm experiments and that found along the environmental gradient were discussed. The results of this study provided strong evidence for the ability of heavy metals to co-select for antibiotic resistance and is the only study that has assessed co-selection of antibiotics and heavy metals in boreal forest soils. (Less)
Popular Abstract
Heavy metal pollution in the environment and antibiotic resistance

Antibiotic resistance is one of the biggest problems humans are facing today. Antibiotics resistance occurs naturally but human activities, such as the use and misuse of antibiotics on humans and animals, has been linked to a proliferation of antibiotic resistance in different environments. Soil is one of the largest and most diverse microbial habitats on earth and represents a vast terrestrial reservoir of antibiotic resistance. Over the past decade there has been increasing interest in the ability of non-antibiotic compounds, such as heavy metals, to co-select for antibiotic resistance in soils. This is of particular concern since unlike antibiotics, metals persist in... (More)
Heavy metal pollution in the environment and antibiotic resistance

Antibiotic resistance is one of the biggest problems humans are facing today. Antibiotics resistance occurs naturally but human activities, such as the use and misuse of antibiotics on humans and animals, has been linked to a proliferation of antibiotic resistance in different environments. Soil is one of the largest and most diverse microbial habitats on earth and represents a vast terrestrial reservoir of antibiotic resistance. Over the past decade there has been increasing interest in the ability of non-antibiotic compounds, such as heavy metals, to co-select for antibiotic resistance in soils. This is of particular concern since unlike antibiotics, metals persist in soils, and are more likely to accumulate and exert toxic effects on soil bacteria.

One of the strongest single point sources of heavy metal pollution in Sweden is the smelter Rönnskär, which is located in Skellefteå, in northern Sweden. It was established in the 1930s and has been emitting a range of heavy metals to the environment ever since. The aim of this study was to determine whether heavy metal pollution from the smelter co-selected for antibiotic resistance in soil bacterial communities. To test this, soil samples with varying metal concentrations were collected between c. 1 and 45 km from the smelter. First, soil microbial composition and process rates were determined for each of the soil samples. Then, a method called pollution induced community tolerance was used to test the ability of metals to co-select for antibiotic resistance. The expectation was that communities more tolerant to copper, would also be more tolerant to the antibiotics tetracycline and vancomycin. Copper was chosen because we knew from previous studies that there were high concentrations of copper in the soils. Tetracycline and vancomycin were chosen because one is very common in the environment (tetracycline) and one is more rare (vancomycin).

The results showed that microbial community composition was significantly affected by heavy metal pollution. It also found a suppression of bacteria and their ecological functions (decomposition) at higher metal concentrations. Bacterial tolerance to copper increased with increasing total copper concentrations and bacterial communities more tolerant to copper were also more tolerant to tetracycline (see figure) but not to vancomycin. These findings provided strong evidence for the ability of environmentally relevant concentrations of metals to co-select for antibiotic resistance and is the only study that has specifically looked at boreal forest soils. This is significant since boreal forests make up a large proportion of the landscape in northern Sweden, where smelting and mining are important industries. We suggest that future research focus on the dominating mechanisms behind co-selection as well as the potential clinical implications, for example what is the risk of resistance genes spreading from soil environments to medically harmful bacteria?

Master’s Degree Project in Biology, 45 credits, 2018
Department of Biology, Lund University

Advisors: Johannes Rousk and Margarida Soares
Microbial Ecology (Less)
Please use this url to cite or link to this publication:
author
Rabow, Sandra
supervisor
organization
course
BION02 20181
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8965390
date added to LUP
2019-01-08 13:58:05
date last changed
2019-01-08 13:58:05
@misc{8965390,
  abstract     = {Due to the public health threat that antibiotic resistance poses to humanity, there is increasing interest for understanding the mechanisms behind the development and transfer of antibiotic resistance genes (ARGs) in different environments. Soil is one of the largest and most diverse microbial habitats on earth and represents a vast terrestrial reservoir of organisms with tolerance to antibiotics. In addition to antibiotics, non-antibiotic compounds, such as heavy metals, have also been shown to co-select for antibiotic resistance in soils. This is of particular concern since unlike antibiotics, heavy metals persist in soils, more likely to accumulate and exert toxic effects on soil bacteria. In this study, samples with a wide range of heavy metal concentrations were collected from coniferous forest soils surrounding the smelter Rönnskär in northern Sweden. First, using PLFA analysis and different methods for measuring process rates (thymidine incorporation, acetate-in-ergosterol, and CO2 production), it was shown that heavy metals from the smelter Rönnskär had a significant impact on microbial community composition, bacterial growth rates and overall microbial activity. Using a pollution induced community tolerance (PICT) approach, this study then provided strong, direct evidence that heavy metal pollution selected for bacterial tolerance to copper (Cu) at soil concentrations exceeding c. 200 mg kg-1 and co-selected for tolerance to the antibiotic tetracycline. In a short term microcosm experiment, Cu exposure induced Cu-tolerance. This, however, did not translate into an induced co-tolerance to tetracycline. The difference between co-tolerance in the microcosm experiments and that found along the environmental gradient were discussed. The results of this study provided strong evidence for the ability of heavy metals to co-select for antibiotic resistance and is the only study that has assessed co-selection of antibiotics and heavy metals in boreal forest soils.},
  author       = {Rabow, Sandra},
  language     = {eng},
  note         = {Student Paper},
  title        = {Do heavy metals select for bacterial tolerance to antibiotics in soils?},
  year         = {2018},
}