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Abstract BackgroundAnthropogenic activities have increased the inputs of atmospheric reactive nitrogen (N) into terrestrial ecosystems, affecting soil carbon stability and microbial communities. Previous studies have primarily examined the effects of nitrogen deposition on microbial taxonomy, enzymatic activities, and functional processes. Here, we examined various functional traits of soil microbial communities and how these traits are interrelated in a Mediterranean-type grassland administrated with 14 years of 7 g m−2year−1of N amendment, based on estimated atmospheric N deposition in areas within California, USA, by the end of the twenty-first century. ResultsSoil microbial communities were significantly altered by N deposition. Consistent with higher aboveground plant biomass and litter, fast-growing bacteria, assessed by abundance-weighted average rRNA operon copy number, were favored in N deposited soils. The relative abundances of genes associated with labile carbon (C) degradation (e.g.,amyAandcda) were also increased. In contrast, the relative abundances of functional genes associated with the degradation of more recalcitrant C (e.g.,mannanaseandchitinase) were either unchanged or decreased. Compared with the ambient control, N deposition significantly reduced network complexity, such as average degree and connectedness. The network for N deposited samples contained only genes associated with C degradation, suggesting that C degradation genes became more intensely connected under N deposition. ConclusionsWe propose a conceptual model to summarize the mechanisms of how changes in above- and belowground ecosystems by long-term N deposition collectively lead to more soil C accumulation.
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This content will become publicly available on August 21, 2026
Conserved pathway for homarine catabolism in environmental bacteria
Abstract Homarine (N-methylpicolinic acid) is a ubiquitous marine metabolite produced by phytoplankton and noted for its bioactivity in marine animals, yet its microbial degradation pathways are uncharacterized. Here, we identify a conserved operon (homABCDER) that mediates homarine catabolism in bacteria using comparative transcriptomics, mutagenesis, and targeted knockouts. Phylogenetic and genomic analyses show this operon distributed across abundant bacterial clades, including coastal copiotrophs (e.g., Rhodobacterales) and open-ocean oligotrophs (e.g., SAR11, SAR116). High-resolution mass spectrometry revealed N-methylglutamic acid and glutamic acid as key metabolic products of homarine in both model and natural systems, with N-methylglutamate dehydrogenase catalyzing their conversion. Metatranscriptomics showed responsive and in situ expression of hom genes aligned with homarine availability. These findings uncover the genetic and metabolic basis of homarine degradation, establish its ecological relevance, and highlight homarine as a versatile growth substrate that feeds into central metabolism via glutamic acid in diverse marine bacteria.
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- Award ID(s):
- 2125886
- PAR ID:
- 10655058
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Research Square
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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