With compound-specific isotope fractionation analysis (CSIA) of chemical trace contaminants (“micropollutants”) the ERC project MicroDegrade could break ground in revealing bottlenecks of degradation at low, relevant (mg/L) concentrations. When enzyme-associated isotope effects were observable, this provided evidence that molecules could diffuse freely into and out of bacterial cells demonstrating that mass transfer was not limiting. In contrast, if isotope fractionation was pronounced at high concentrations, but isotope effects were masked at trace levels, this provided evidence that mass transfer into and out of the cell became limiting for biodegradation specifically at low concentrations (Ehrl et al., Environ. Sci. Technol. 2019, Marozava et al. Environ. Sci. Technol. 2019).
Sun et al. 2021 b


With the ability to directly observe mass transfer limitation, and to characterize associated physiological adaptation MicroDegrade has introduced a novel analytical approach to the investigation of microbial activity at low concentrations. It also brings forward a mechanistic explanation for the “persistence by dilution” hypothesis: that low-level water constituents such as NOM may not persistent because of inherent recalcitrance, but because of low concentrations. For Isotope Biogeochemistry the project’s findings have pronounced implications for the interpretation of isotope profiles at low concentrations: they imply that, based on isotopic evidence, turnover of substances at low concentrations may have been underestimated so far.
For bioremediation approaches of low-level concentrations, the direct observation of limitations offers an enabling tool to identify the relevant bottlenecks. Pillaring on this, we found that fluctuations in concentrations are generally faster than build-up and decay of degrader biomass, yet can profoundly influence bacterial adaptation and diversification (Kundu et al., Environ. Microbiol. 2020). Hence, variations in substrate concentrations and flow conditions may be a promising remediation approach.



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    DOI: (b)
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