bioRxiv Science⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.64898/2026.11.05.764102

Asymmetric division and polar growth define a non-canonical cell cycle in Bradyrhizobium.

Medici, I. F.·Bressano, J.·Comerci, D. J.·Mongiardini, E. J.·Lioy, V. S.·Soler-Bistue, A.
View original source ↗Export metadata ↓

Abstract

Bradyrhizobia are widely used as plant growth promoters in agriculture, yet their cell biology remains poorly understood. Here, we described for the first time, nucleoid segregation dynamics and the cell cycle of Bradyrhizobium at the cellular level. We show that highly asymmetric polar growth generates a short daughter cell and a longer mother cell at each division. Nucleoid compaction and positioning change across growth phases, culminating in a highly compacted, asymmetrically positioned nucleoid in stationary phase. ParB presents a subpolar localization, at the nucleoid periphery. Despite this pronounced cellular asymmetry and the presence of a single large chromosome, chromosome conformation capture reveals a global chromosome organization similar to that of bacteria undergoing conventional binary fission Together, these findings uncover a distinctive cell cycle program in Bradyrhizobium. showing that such extreme asymmetry in growth and division, significantly different from closely related characterized -Proteobacteriota, is compatible with conserved principles of chromosome organization.

Explore related subjects

microbiologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Medici, I. F., Bressano, J., Comerci, D. J., Mongiardini, E. J., Lioy, V. S., Soler-Bistue, A.. 2026-11-06. Asymmetric division and polar growth define a non-canonical cell cycle in Bradyrhizobium.. https://doi.org/10.64898/2026.11.05.764102

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Genomic analysis of the Streptococcus anginosus group; taxonomic implications, evolutionary insights and clinical considerations

Background: The Streptococcus anginosus group (SAG) (S. anginosus, S. intermedius, and S. constellatus) causes serious, potentially life-threatening, invasive infections, often in otherwise healthy individuals. However, the group's diversity is still poorly understood, and with it, the ability to identify prognostic markers of severe disease. Methods: Long-read sequencing produced closed genomes for 29 isolates from 25 patients hospitalised primarily for invasive SAG infections, and 21 isolates from 20 non-hospitalised controls. Genomes were classified with GTDB-Tk and combined with 211 reference genomes. After dereplication, 207 SAG genomes (38 isolate, 169 reference) representing 206 strains were analysed using: GTDB classification, average nucleotide identity, multi-marker and core-genome SNP phylogenies, recombination-aware analyses, mobilome, CAZyme and gapseq metabolic profiling, and lineage-aware genome-wide association testing for invasive phenotype. Results: Agreement between GTDB-Tk and MALDI-TOF taxonomic classifications was low (42.8%), including two S. massiliensis cases mis-identified by MALDI-TOF as SAG. S. anginosus resolved into four taxa (S. anginosus, S. hominis, S. whileyi and S. vaginalis). Phylogenies based on core genome single-nucleotide polymorphisms resolved these species into distinct clades, whereas 16S rRNA gene and multilocus sequence analysis phylogenies did not. The four ex-S. anginosus taxa showed a gradient of genomic cohesion, with S. vaginalis being near-clonal, in contrast to S. anginosus, which shared high levels of sequence ancestry with other neighbouring taxa. Carbohydrate utilisation was strongly lineage-associated, as was propensity for invasive disease. A ~15Kbp glycosaminoglycan utilisation locus was found in the three taxa of highest disease severity propensity (S. intermedius, S. constellatus, S. whileyi) which predicts a direct host glycosaminoglycan feeding mechanism that may contribute to invasive disease. No single functional feature, gene or core-genome SNP was associated with invasiveness however after lineage-adjustment. Combined feature analysis suggests S. vaginalis has undergone a niche restriction and has evolved for a primary existence in the female urogenital tract. Conclusions: Under-reported species may be mis-diagnosed as SAG invasive infections. SAG is more diverse than its current three-species definition, with the conventional S. anginosus species proposed to be classed into a complex of four distinct taxa. Invasive capacity appears to be an emergent system-level property rather than from individual features.

microbiology↗
bioRxiv2026

Cell-scale confinement reorders bacterial speed rankings

Which bacterium swims fastest depends on where the race is run. Speeds are usually measured in open liquid, yet many bacteria live in pores, mucus and host passages no wider than a cell. Using a microfluidic device with eight channel widths (0.80-3.00 m) in one field of view, we tracked unlabeled cells of eight species spanning five motility systems. Chamber height, a polymer additive and channel width each reordered the ranking. Vibrio alginolyticus, the fastest in open liquid, slowed to ~4 m/s in 1.25-m channels, whereas Campylobacter jejuni and Bacillus subtilis kept 33-46 m/s. Open liquid speed did not predict robustness to confinement. In two unrelated lineages, host symbionts that pass through narrow passages during colonization, Caballeronia insecticola and Vibrio fischeri, outran their non-symbiotic relatives in the channels, and crossed them with flagella wrapped around the cell body at nearly the speed of unwrapped cells. Where space is tight, the ability to keep moving, not top speed, sets the ranking.

microbiology↗
bioRxiv2026

The biochemical composition of coronavirus Nucleocapsid proteins drives the bicistronic properties of their sub-genomic mRNAs

The nucleocapsid (N) gene of coronaviruses (CoVs) encodes a structural RNA-binding protein required for viral assembly. In SARS- and MERS-CoV viruses, reading frame 2 of N contains an overlapping open reading frame (ORF) encoding an innate immune antagonist accessory protein. However, the extent of this dual coding capacity across the CoV family, and the genetic features driving overlapping ORF formation, remain unexamined. Here, we developed an in-silico tool (ORFan) to screen structural gene sub-genomic mRNA sequences from 152 species of coronavirus for the presence of overlapping accessory gene candidates. We found that frame 2 of the N gene in Alpha-, Beta- and Delta-CoVs frequently contains a potential accessory ORF (AcORF), conserved at the subgenus level, unlike the spike, envelope and membrane genes. We also show that CoV nucleotide biases in conjunction with codon biases integral to N protein function drive the relatively high abundances of start codons in frame two and stop codons in frame three, explaining the tendency towards frame 2 AcORFs. We further suggest that viral nucleotide biases and the codon composition required for RNA-binding function facilitate overlapping ORF formation in other virus families

microbiology↗