Kondrot, F. | Search bioRxiv

bioRxiv2026

The cost-benefit trade-off of peritrichous flagellation in bacteria

Many bacteria assemble multiple flagella, although building flagella imposes a substantial biosynthetic and energetic cost. We used the peritrichously flagellated model organism Salmonella enterica to quantify how flagellar abundance affects bacterial growth, proteome allocation, and motility. For this, we generated genetically modified strains with inducible or constitutive expression of the flagellar master regulator flhDC, resulting in a panel of strains ranging from nearly non-flagellated to hyperflagellated cells. We found that higher flagellar investment reduced growth rate and redirected proteome allocation, with an expansion of the flagellar sector occurring largely at the expense of the ribosomal sector. Growth analyses of flagellar assembly mutants, combined with cost modeling, suggested that flagellin biosynthesis dominated the energetic burden, whereas motor rotation contributed a smaller additional cost. Despite the associated cost, increased flagellation improved soft-agar spreading, single-cell swimming speed, effective diffusivity, and competitive fitness in spatially structured environments. A coarse-grained proteome-allocation model parametrized from these data reproduced the observed growth penalties, while simulations of navigation in dynamic chemical gradients predicted that motility benefits saturate near a flagellar investment of 3% of proteome mass. Beyond this point, rising biosynthetic costs outweigh diminishing motility gains. In summary, these results support a quantitative cost-benefit model in which heterogeneous, spatially structured environments favor an intermediate number of flagella by balancing motility benefits against the biosynthetic costs of building and operating multiple flagella.

microbiology↗

bioRxiv2025

Targeting the translation machinery: The RNase Y specificity factor Y-complex coordinates ribosome degradation

Limiting the synthesis and activity of ribosomes is crucial for adaptation to stresses, such as heat or nutrient starvation. In Bacillus subtilis, this can be achieved through the coordinated action of the alarmones (p)ppGpp and the transcription factor Spx. Here, we performed a genetic screen to uncover novel factors contributing to the heat shock response of B. subtilis. We identified the Y-complex, which confers specificity to the endonuclease RNase Y, as a critical player during stress conditions, such as heat or transition into stationary phase. This protein complex is required for processing diverse RNAs, notably the maturation of mRNAs encoding proteins involved in translation and metabolism. We further demonstrate that the Y-complex and RNase Y initiate the degradation of rRNAs of mature ribosomes, lowering their abundance. We propose that the Y-complex is a regulatory hub that modulates gene expression, adjusts protein synthesis and resource allocation.

microbiology↗