Pett-Ridge, J. A. | Search bioRxiv

bioRxiv2026

Rapid Changes in Transcription During a Feast-Famine Event

AbstractSoil microbes have sophisticated mechanisms to detect and respond to short pulses of C inputs, often involving changes in gene-expression. We studied gene transcription in a soil microbial community before, and 8, 24, and 48h after glucose addition (0.7 mg C g-1 dry soil) to understand how microbes react to periods of substrate excess and subsequent starvation. The relative transcript abundance of genes associated with energy metabolism and biosynthesis of amino acids, lipids, nucleotides, and cell wall components increased 8h after glucose addition. By 24 and 48h, the abundances of these transcripts reversed. Transcript abundance for genes associated with degradation of lipids, nucleotides, and (hetero)cyclic hydrocarbons decreased at 8h, but increased 24 and 48h after glucose addition. Simultaneously with a rise in transcripts for energy production and biosynthesis at 8h, transcription of regulatory genes for the exponential growth phase and ribosome assembly and maturation increased. In contrast, at 24 and 48h, transcript abundance for genes associated with ribosomal hibernation, sporulation, and regulation of the stationary phase increased, while transcripts for regulators for the exponential phase, and ribosome activation decreased. Based on changes in transcript abundance of phosphoenolpyruvate carboxylase and pyruvate carboxylase, it appeared that 8h after glucose addition glycolytic activity was high, however, gluconeogenesis returned at 24 and 48h. High levels of transcripts for nrtC-ntrB indicated N limitation 8 and 24h after glucose addition. Transcripts associated with Type VI Secretion Systems increased 24 and 48h after start of the experiment, suggesting a short lag between primary consumers and predatory bacteria. These results illustrate how metatranscriptome analysis can be used to study the ecophysiology of soil microbes providing details on the timing of exponential and stationary phase processes, coordination between anabolism and catabolism, and emerging nutrient limitations in natural soil communities. Research HighlightsO_LIWe studied gene transcription of a soil microbial community after glucose addition C_LIO_LITranscript abundances for biosynthesis and energy production initially increased, while those for degradation decreased C_LIO_LITranscripts of regulators and sporulation genes indicated start of stationary phase at 24h C_LIO_LINitrogen limitation induced transcription of nitrogen stress genes C_LI

ecology↗

bioRxiv2021

Edaphic controls on genome size and GC content of bacteria in soil microbial communities

Bacteria in soil microbial communities are crucial to terrestrial ecosystem function, yet our understanding of the fundamental characteristics of their genomes, such as GC content and genome size, is not complete. Much of our understanding of the mechanisms which shape their genomic traits is derived from other systems or from isolated bacteria. Here we determined average genome size, GC content, codon usage, and amino acid content from 398 soil metagenomes across a broad geographic range and used machine-learning to determine which environmental parameters most strongly explain the distribution of these traits. We found that genomic trait averages were most related to pH, which we suggest is primarily due to the correlation of pH with several environmental parameters, especially soil carbon content. Low pH soils had higher carbon to nitrogen ratios (C:N) and tended to have communities with lower GC content and larger genomes, potentially a response to increased physiological stress and a requirement for metabolic diversity. Conversely, smaller genomes with high GC content were associated with high pH and low soil C:N, indicating potential resource driven selection against AT base pairs. As soil bacteria tend to be more carbon limited, smaller genomes with higher GC content may reduce the cost of reproduction in carbon-limited soils. Similarly, we found that nutrient conservation also applied to amino acid stoichiometry, where bacteria in soils with low C:N ratios tended to code for amino acids with lower C:N. Together, these relationships point towards fundamental mechanisms that underpin nucleotide and amino acid selection in soil bacterial communities.

ecology↗