Metal contamination causes metabolic stress in environmental bacteria, study shows

Metal contamination causes metabolic stress in environmental bacteria

Left: the subsurface at Drumna Darach Reserve has high levels of multiple metals, affecting the growth and metabolism of native bacteria. Right: proteomic response to metal exposure. Lines connect exposure conditions (white circles) to individual proteins. Credit: Modified from Goff, JL, et al., Mixed heavy metal stress triggers a global response to iron starvation, ISME Magazine (2022). The original image is licensed under a Creative Commons Attribution 4.0 International License

Contamination of soil and water with multiple heavy metals is a common problem. However, most studies on the effects of heavy metals on bacteria living in these environments have only focused on one metal at a time. In a recent study, researchers found that bacteria exposed to a mixture of metals caused their metabolism to change. The researchers did not observe this change when bacteria were grown with only metal. Experiments indicate that some metals occurred due to the presence of cells “thinking” they were hungry for iron. This is likely to change the way bacteria behave in the environment, as many bacterial enzymes require iron.

The results are published in ISME Magazine.

The researchers explored how heavy metal exposure changes the behavior of bacteria living in a polluted environment. Understanding such behavior helps us understand nutrient cycling and pollutant removal or clearance. ​​​​The study found that exposure to a metal mixture interferes with iron-dependent bacterial processes. This is important because many bacterial enzymes involved in nutrient cycling and pollutant cleaning require iron to function properly.

Urbanization, agricultural practices, and industrial activities have left many global environments contaminated with elevated levels of multiple heavy metals. Elevated metal concentrations can disrupt microbially driven biogeochemical cycling. However, few studies have explored the effects of multiple metals on microbial physiology. This study focused on the subsurface of the Department of Energy’s Oak Ridge Reservation (ORR) in Oak Ridge, Tennessee. The site has elevated concentrations of multiple metals and nitrates.

Metal contamination causes metabolic stress in environmental bacteria

Map and geochemical parameters of the Oak Ridge Reservation (ORR) contamination study site. Map showing the location of the ORR in the United States (USA). The SAM map was generated with the get_stamenmap function in the ggmap R package implemented in RStudio [88]. The inset map shows the study site: the subsurface regions immediately adjacent to the former S-3 ponds (indicated by the yellow, dashed box). Field 3 is marked with a red, colored box. The site of CPTF isolation is described in Goff et al. (2022) also marked. Distribution of (b) nitrate (mM) and (c) uranium (µM) in Area 3 groundwater and in groundwater samples taken from two locations close to Area 3 and the former S-3 ponds. All satellite maps were generated in Google My Maps. Images: 2022 Maxar Technologies. Map data: 2022 US Geological Survey. Credit: ISME Magazine (2022). DOI: 10.1038/s41396-022-01351-3

Using a native bacterial isolate that represents a highly abundant species at this site, researchers from the University of Georgia, Lawrence Berkeley National Laboratory, and the Scripps Center for Metabolomics examined the effects of combined metal exposure (eight metals at concentrations relevant to the site) through. a multi-omics approach. Parallel experiments investigated the effects of individual metal constituents.

Exposure to a combination of metals affected cell physiology in a way that was greater than the cumulative effect of the individual metal exposures. Specifically, multiple metal-exposed iron homeostasis is deregulated, which initiates the canonical iron starvation response. This disruption of iron homeostasis by the metal mixture inhibited the activity of two critical enzymes that use iron cofactors to remove nitrate in the ORR subsurface: the nitrate and nitrite reductases. These results highlight the need to move from single to multi-metal studies to better assess the impact of these stressors on indigenous microbial systems.

More information:
Jennifer L. Goff et al, Mixed heavy metal stress triggers a global response to iron starvation, ISME Magazine (2022). DOI: 10.1038/s41396-022-01351-3

Available from US Department of Energy

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