Biology subjects

Ohbayashi, T.

Publications and source records attributed to Ohbayashi, T..

3 recordsLinked to original sources

bioRxiv2025

Single-cell genomics of single soil aggregates: methodological assessment and potential implications with a focus on nitrogen metabolism

Soil particles in plant rooting zone are largely clustered to form complex porous structural unit called aggregates where highly diverse microbes coexist and drive biogeochemical cycling. The complete extraction of microbial cells and DNA from soil is a substantial task as certain microbes exhibit strong adhesion to soil surfaces and/or inhabit deep within aggregates. Yet, the degree of aggregate dispersion and the efficacy of extraction have rarely been examined, and thus adequate cell extraction method from soil remain unclear. We aimed to develop an optimal method of cell extraction for single-cell genomics (SCG) analysis of single soil aggregates by focusing on water-stable macroaggregates (diameter: 5.6-8.2 mm) isolated from a topsoil of cultivated Acrisol. Using the same six individual aggregates, we performed both SCG sequencing and amplicon analysis. While both bead-vortexing and sonication dispersion methods improved the extractability of bacterial cells compared to previous studies, the latter yielded higher number and more diverse microbes compared to the former. The analyses of nitrogen-cycling and exopolysaccharides-related genes suggested that the sonication-assisted extraction led to greater recovery of microbes strongly attached to soil particles and/or inhabited the aggregate subunits that were more physically stable (e.g., aggregate core). Further SCG analysis revealed that all six aggregates held intact microbes having the genes (i.e., potentials) to convert nitrate into all possible nitrogen forms while some low-abundance genes showed inter-aggregate heterogeneity. In addition, all six aggregates studied showed overall similarity in pore characteristics, phylum-level composition, and the microbial functional redundancy. Together, these results suggest that water-stable macroaggregates may act as a functional unit in soil and show potential as a useful experimental unit in soil microbial ecology. Our study also suggest that conventional methods employed for the extraction of cell and DNA may not be optimal. The current findings underscore the necessity to advance extraction methodologies, thereby facilitating a more comprehensive understanding of the microbial diversity and functioning within soil environments.

microbiology↗

bioRxiv2023

Hundreds of antimicrobial peptides create a selective barrier for insect gut symbionts

The spatial organization of gut microbiota is crucial for the functioning of the gut ecosystem, although the mechanisms that organize gut bacterial communities in microhabitats are only partially understood. The gut of the insect Riptortus pedestris has a characteristic microbiota biogeography with a multispecies community in the anterior midgut and a mono-specific bacterial population in the posterior midgut. We show that the posterior midgut region produces massively hundreds of specific antimicrobial peptides (AMPs), the Crypt-specific Cysteine-Rich peptides (CCRs) that have membrane-damaging antimicrobial activity against diverse bacteria but posterior midgut symbionts have elevated resistance. We determined by transposon-sequencing the genetic repertoire in the symbiont Caballeronia insecticola to manage CCR stress, identifying different independent pathways, including novel AMP-resistance pathways unrelated to known membrane homeostasis functions as well as cell envelope functions. Mutants in the corresponding genes have reduced capacity to colonize the posterior midgut, demonstrating that CCRs create a selective barrier and resistance is crucial in gut symbionts. Moreover, once established in the gut, the bacteria differentiate into a CCR-sensitive state, suggesting a second function of the CCR peptide arsenal in protecting the gut epithelia or mediating metabolic exchanges between the host and the gut symbionts. Our study highlights the evolution of an extreme diverse AMP family that contributes to establish and control the gut microbiota.

microbiology↗

bioRxiv2023

Transposon sequencing reveals the essential gene set and genes enabling gut symbiosis in the insect symbiont Caballeronia insecticola

Caballeronia insecticola is a bacterium belonging to the Burkholderia genus sensu lato, able to colonize multiple environments like soils and the gut of the bean bug Riptortus pedestris. To identify the essential genome of a bacterium is a first step in the understanding of its lifestyles. We constructed a saturated Himar1 mariner transposon library and revealed by transposon-sequencing (Tn-seq) that 498 protein-coding genes constitute the essential genome of C. insecticola for growth in free-living conditions. By comparing essential gene sets of C. insecticola and seven related Burkholderia s.l. strains, only 120 common genes were identified indicating that a large part of the essential genome is strain-specific. In order to reproduce specific nutritional conditions that are present in the gut of R. pedestris, we grew the mutant library in minimal media supplemented with candidate gut nutrients and identified several condition-dependent fitness-defect genes by Tn-seq. To validate the robustness of the approach, insertion mutants in six fitness genes were constructed and their growth-deficiency in media supplemented with the corresponding nutrient was confirmed. The mutants were further tested for their efficiency in R. pedestris gut colonization, confirming that gluconeogenic carbon sources, taurine and inositol, are nutrients consumed by the symbiont in the gut.

microbiology↗