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Tracking the metabolic activity of whole soil communities can improve our understanding of the transformation and fate of carbon in soils. We used stable isotope metabolomics to trace 13C from nine labeled carbon sources into the water-soluble metabolite pool of an agricultural soil over time. Soil was amended with a mixture of all nine sources, with one source isotopically labeled in each treatment. We compared changes in the 13C enrichment of metabolites with respect to carbon source and time over a 48-day incubation and contrasted differences between soluble sources (glucose, xylose, amino acids, etc.) and insoluble sources (cellulose and palmitic acid). Whole soil metabolite profiles varied singularly by time, while the composition of 13C-labeled metabolites differed primarily by carbon source (R2 = 0.68) rather than time (R2 = 0.07), with source-specific differences persisting throughout incubations. The 13C labeling of metabolites from insoluble carbon sources occurred slower than that from soluble sources but yielded a higher average atom percent (atom%) 13C in metabolite markers of biomass (amino acids and nucleic acids). The 13C enrichment of metabolite markers of biomass stabilized between 5 and 15 atom% 13C by the end of incubations. Temporal patterns in the 13C enrichment of tricarboxylic acid cycle intermediates, nucleobases (uracil and thymine), and by-products of DNA salvage (allantoin) closely tracked microbial activity. Our results demonstrate that metabolite production in soils is driven by the carbon source supplied to the community and that the fate of carbon in metabolites do not generally converge over time as a result of ongoing microbial processing and recycling. IMPORTANCE Carbon metabolism in soil remains poorly described due to the inherent difficulty of obtaining information on the microbial metabolites produced by complex soil communities. Our study demonstrates the use of stable isotope probing (SIP) to study carbon metabolism in soil by tracking 13C from supplied carbon sources into metabolite pools and biomass. We show that differences in the metabolism of sources influence the fate of carbon in soils. Heterogeneity in 13C-labeled metabolite profiles corresponded with compositional differences in the metabolically active populations, providing a basis for how microbial community composition correlates with the quality of soil carbon. Our study demonstrates the application of SIP-metabolomics in studying soils and identifies several metabolite markers of growth, activity, and other aspects of microbial function.

Microorganisms have evolved various life-history strategies to survive fluctuating resource conditions in soils. However, it remains elusive how the life-history strategies of microorganisms influence their processing of organic carbon, which may affect microbial interactions and carbon cycling in soils. Here, we characterized the genomic traits, exometabolite profiles, and interactions of soil bacteria representing copiotrophic and oligotrophic strategists. Isolates were selected based on differences in ribosomal RNA operon (rrn) copy number, as a proxy for life-history strategies, with pairs of "high" and "low" rrn copy number isolates represented within the Micrococcales, Corynebacteriales, and Bacillales. We found that high rrn isolates consumed a greater diversity and amount of substrates than low rrn isolates in a defined growth medium containing common soil metabolites. We estimated overlap in substrate utilization profiles to predict the potential for resource competition and found that high rrn isolates tended to have a greater potential for competitive interactions. The predicted interactions positively correlated with the measured interactions that were dominated by negative interactions as determined through sequential growth experiments. This suggests that resource competition was a major force governing interactions among isolates, while cross-feeding of metabolic secretion likely contributed to the relatively rare positive interactions observed. By connecting bacterial life-history strategies, genomic features, and metabolism, our study advances the understanding of the links between bacterial community composition and the transformation of carbon in soils.

Climate change is an urgent environmental issue with wide‐ranging impacts on ecosystems and society. Microbes are instrumental in maintaining the balance between carbon (C) accumulation and loss in the biosphere, actively regulating greenhouse gas fluxes from vast reservoirs of organic C stored in soils, sediments and oceans. Heterotrophic microbes exhibit varying capacities to access, degrade and metabolise organic C—leading to variations in remineralisation and turnover rates. The present challenge lies in effectively translating this accumulated knowledge into strategies that effectively steer the fate of organic C towards prolonged sequestration. In this article, we discuss three ecological scenarios that offer potential avenues for shaping C turnover rates in the environment. Specifically, we explore the promotion of slow‐cycling microbial byproducts, the facilitation of higher carbon use efficiency, and the influence of biotic interactions. The ability to harness and control these processes relies on the integration of ecological principles and management practices, combined with advances in economically viable technologies to effectively manage microbial systems in the environment. [ABSTRACT FROM AUTHOR]

Summary: Soil microbial community composition routinely correlates with pH, reflecting both direct pH effects on microbial physiology and long‐term biogeochemical feedbacks. We used two watershed‐scale liming experiments to identify short‐ (2 years) and long‐term (25 years) changes in the structure and function of bacterial and fungal communities in organic horizons (Oe and Oa) of acid forest soils. Liming increased soil pH, extractable calcium, and soil carbon stocks, reduced biomass‐specific respiration, and caused major changes in the soil microbiome in the short and long term. More taxa responded to liming in the short term (70%) than in the long term (30%), with most showing consistent directional responses at both sites. The ratio of change in relative abundance between limed and reference sites was twofold higher at the long than the short‐term site, indicating that the effects of liming grew over time. Liming impacts were most pronounced in fungi, as steep declines of dominant ectomycorrhizal fungi (Cenococcum and Russula) occurred at both sites. Liming favoured neutrophilic bacteria over acidophilic populations according to estimated environmental pH optima. Collectively, these results demonstrate that a liming‐induced change of one pH unit has an immediate and persistent effect on the structure and function of microbial communities in acid forest soils. The corresponding suppression of respiration indicates that anthropogenic alterations of soil pH, as driven by acid deposition or liming, can affect forest floor C stocks due to pH‐driven shifts in community structure. [ABSTRACT FROM AUTHOR]

A viral etiology of sea star wasting syndrome (SSWS) was originally explored with virus-sized material challenge experiments, field surveys, and metagenomics, leading to the conclusion that a densovirus is the predominant DNA virus associated with this syndrome and, thus, the most promising viral candidate pathogen. Single-stranded DNA viruses are, however, highly diverse and pervasive among eukaryotic organisms, which we hypothesize may confound the association between densoviruses and SSWS. To test this hypothesis and assess the association of densoviruses with SSWS, we compiled past metagenomic data with new metagenomic-derived viral genomes from sea stars collected from Antarctica, California, Washington, and Alaska. We used 179 publicly available sea star transcriptomes to complement our approaches for densovirus discovery. Lastly, we focus the study on sea star-associated densovirus (SSaDV), the first sea star densovirus discovered, by documenting its biogeography and putative tissue tropism. Transcriptomes contained only endogenized densovirus elements similar to the NS1 gene, while numerous extant densoviral genomes were recovered from viral metagenomes. SSaDV was associated with nearly all tested species from southern California to Alaska, and in contrast to previous work, we show that SSaDV is one genotype among a high diversity of densoviruses present in sea stars across the West Coast of the United States and globally that are commonly associated with grossly normal (i.e., healthy or asymptomatic) animals. The diversity and ubiquity of these viruses in sea stars confound the original hypothesis that one densovirus is the etiological agent of SSWS. [ABSTRACT FROM AUTHOR]