Mediterranean Grassland qSIP Rainfall-Gradient Community

DNA isotope incorporation in rewetted grassland soil microcosms supported population-specific growth/activity estimates over an eight-day laboratory incubation. Genome-resolved qSIP linked these estimates to genomic traits. This is a positive biological growth observation, not labeling or genome assembly as an ecological mechanism. Low versus high activity is relative to the site mean; low labeling does not establish death or absolute inactivity. Gross incorporation over the incubation is not instantaneous replication, net population increase or movement measured in the field. The two canonical Bacteria entries are overlapping aggregate guild placeholders, not a resolved complete roster.

Evidence

• PMID:36300946 - SUPPORT (IN_VITRO)
  "genome-resolved metagenomic implementation of quantitative stable isotope probing (qSIP) with an H218O labeling experiment"
• PMID:36300946 - SUPPORT (COMPUTATIONAL)
  "isotopic incorporation into microbial DNA requires production of new genome copies"
• PMID:36300946 - SUPPORT (COMPUTATIONAL)
  "qSIP-informed genome-resolved metagenomics to resolve the active subset of soil community members and identify their characteristic ecophysiological traits"

Across three California Mediterranean-climate grassland sites, historical mean precipitation was associated with community composition and activity patterns. The source tests a historical environmental-selection hypothesis, not randomized long-term rainfall treatment. Soil was sampled during the wet season, dried and rewetted for laboratory incubation; similar incubation water potential does not remove all site-history confounding. Preserve the observed association without asserting directly measured niche partitioning or a community-to-community causal arrow.

Evidence

• PMID:36300946 - PARTIAL (COMPUTATIONAL)
  "three Mediterranean grassland soils across a rainfall gradient"
• PMID:36300946 - PARTIAL (COMPUTATIONAL)
  "historic precipitation levels are an important factor controlling trait selection"

Genomes encoding complete or mostly complete flagellar gene suites were enriched among active organisms from the wetter Angelo and Hopland sites compared with Sedgwick. Activity was inferred by qSIP; motility was predicted from genes, not observed cell trajectories or a flagellar perturbation. Higher moisture could favor movement and resource access, but this remains an interpretation of a cross-site association. Active Bdellovibrio contributed to the pattern; exact prey, predation rates and necromass production were not measured here.

Biological Processes:

• bacterial-type flagellum-dependent cell motility (GO:0071973 · PathwayMech)

Evidence

• PMID:36300946 - PARTIAL (COMPUTATIONAL)
  "higher activity and growth rates of flagellar motile microorganisms"

Genomic capacities for complex-carbohydrate degradation, methanol oxidation and carbon-monoxide oxidation were broadly distributed across soils and activity levels, rather than universally enriched among growing organisms at wetter sites. Specific site/taxon associations remained, including methanol-dehydrogenase-bearing genomes with higher activity at Angelo. Annotation plus organism-level DNA labeling is not substrate-specific flux, expression, a complete carbon budget, or proven sequestration. Broadly shared capacities do not establish partitioned carbon niches.

Evidence

• PMID:36300946 - SUPPORT (COMPUTATIONAL)
  "the capacity to decompose the diverse complex carbohydrates common in soil organic matter or oxidize methanol and carbon monoxide were broadly distributed across active and inactive bacteria"