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This paper presents three novel findings about the interaction of sunlight and microbes during the degradation of terrigenous dissolved organic matter (DOM) in aquatic systems. First, it shows that sunlight can replace the function of certain microbial enzymes, which provides an energy savings for microbes and increases their investment in growth. Second, differential gene expression provides a new, genomics-based line of evidence for the mechanisms of photo-alteration of DOM and demonstrates the effects of these mechanisms on microbes and specific metabolic functions (through metatranscriptomics). Third, it provides the first evidence of how decarboxylation of DOM by sunlight impacts microbes.
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Experimental metatranscriptomics reveals the costs and benefits of dissolved organic matter photo‐alteration for freshwater microbes
Microbes and sunlight convert terrigenous dissolved organic matter (DOM) in surface waters to greenhouse gases. Prior studies show contrasting results about how biological and photochemical processes interact to contribute to the degradation of DOM. In this study, DOM leached from the organic layer of tundra soil was exposed to natural sunlight or kept in the dark, incubated in the dark with the natural microbial community, and analyzed for gene expression and DOM chemical composition. Microbial gene expression (metatranscriptomics) in light and dark treatments diverged substantially after 4 hours. Gene expression suggested that sunlight exposure of DOM initially stimulated microbial growth by (a) replacing the function of enzymes that degrade higher molecular weight DOM such as enzymes for aromatic carbon degradation, oxygenation, and decarboxylation, and (b) releasing low molecular weight compounds and inorganic nutrients from DOM. However, growth stimulation following sunlight exposure of DOM came at a cost. Sunlight depleted the pool of aromatic compounds that supported microbial growth in the dark treatment, ultimately causing slower growth in the light treatment over 5 days. These first measurements of microbial metatranscriptomic responses to photo-alteration of DOM provide a mechanistic explanation for how sunlight exposure of terrigenous DOM alters microbial processing and respiration of DOM.
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- Award ID(s):
- 1754835
- PAR ID:
- 10169582
- Date Published:
- Journal Name:
- Environmental Microbiology
- ISSN:
- 1462-2912
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/1462‐2920.15121
