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Different resource allocation in a Bacillus subtilis population displaying bimodal motility

ABSTRACT: To cope with sudden changes in their environment, bacteria can use a bet-hedging strategy by dividing the population into cells with different properties. This so called bimodal or bistable cellular differentiation is generally controlled by positive feedback regulation of transcriptional activators. Due to continued turnover of the cytoplasmic content, it is difficult for these activators to reach an activation threshold concentration when cells are growing exponentially. This is one reason why bimodal differentiation is primarily observed from the onset of the stationary phase when exponential growth ceases. An exception is the bimodal induction of motility in Bacillus subtilis, which occurs early during exponential growth. Several mechanisms have been put forward to explain this, including double negative-feedback regulation and the stability of the mRNA molecules involved. In this study, we used fluorescence-assisted cell sorting to compare the transcriptome of motile and non-motile cells and noted that expression of ribosomal genes is lower in motile cells. This was confirmed using an unstable GFP reporter fused to the strong ribosomal rpsD promoter. We propose that the reduction in ribosomal gene expression in motile cells is the result of a diversion of cellular resources to the synthesis of the chemotaxis and motility systems. In agreement, single-cell microscopic analysis indicates that motile cells are slightly shorter than non-motile cells, an indication of slower growth. We speculate that this growth rate reduction can contribute to the bimodal induction of motility during exponential growth.

ORGANISM(S): Bacillus subtilis

PROVIDER: GSE164348 | GEO | 2021/01/20

REPOSITORIES: GEO

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Project description:The genus Lactobacillus contains over 100 different species that were traditionally considered to be uniformly non-motile. However, at least twelve motile species are known to exist in the L. salivarius clade of this genus. Of these, Lactobacillus rumnis is the only motile species that is also autochthonous to the mammalian gastrointestinal tract. The genomes of two L. ruminis strains, ATCC25644 (human isolate, non-motile) and ATCC27782 (bovine isolate, motile) were sequenced and annotated to identify the genes responsible for flagellum biogenesis and chemotaxis in this species. Transcriptome analysis revealed that motility genes were transcribed at a significantly higher level in motile L. ruminis ATCC27782 than in non-motile ATCC25644 during the motile growth phase. In preparation for RNA isolation from L. ruminis ATCC27782 and ATCC25644 cultures in the motile phase, 20 ml aliquots of MRS broth were inoculated (0.25 % inoculum) with a turbid culture of the desired strain. The cultures were incubated anaerobically at 37 Â°C for 15 hr. In preparation for RNA isolation from L. ruminis ATCC27782 and ATCC25644 cultures in the non-motile growth phase, 20 ml aliquots of MRS broth were inoculated (1 % inoculum) with a turbid culture of the desired strain. The cultures were incubated anaerobically at 37 Â°C for 16-20 hrs. RNAprotect Bacteria reagent (Qiagen) was used to stabilize gene expression in the target cultures, and total RNA was isolated according to the protocol for enzymatic and mechanical disruption of bacteria as described in the RNAprotect Bacteria Reagent handbook. RNA isolation was completed with the RNeasy Mini kit, and contaminating DNA was removed with the Turbo DNA-free kit (Ambion). An Oligo aCGH/ChIP-on chip hybridization kit (Agilent) was used for hybridization of the labelled cDNA to the microarrays. Probe hybridization took place at 65 Â°C for 20 hrs with constant rotation (10 rpm). Microarrays were scanned using the Agilent Microarray Scanner System (G2505B) and the scanned files were converted to data files with Feature Extraction software (Agilent). Three microarrays, (three biological replicates) were used to examine gene transcription during the motile growth phase. One microarray was used to examine gene transcription during the non-motile growth phase.

Project description:Impacts of plasmid carriage on its host cell were comprehensively analyzed using conjugative plasmid pCAR1 in the three different kinds of hosts, Pseudomonas putida KT2440, P. aeruginosa PAO1, and P. fluorescens Pf0-1. Various analyses of the host phenotype showed that pCAR1 carriage reduced host fitness, swimming motility, and resistances to osmotic- or pH-stress, and brought about the alterations of primary metabolic capacities in the TCA cycle or those several steps away from the TCA cycle in the host cells. Growth phase-dependent transcriptome analyses were performed with the classification of the annotated genes based on their identities among the three hosts and their putative functions. pCAR1 carriage affected host transcriptome more greatly at the transition and stationary phases in each host. The transcriptome responses were more similar between KT2440 and PAO1 than between other host combinations, and many genes, such as for ribosomal proteins, F-type ATPase, and RNAP core, in both strains were commonly not suppressed in their stationary phases. These responses may have resulted in the reduction of host fitness, motility, and stress resistances. Host-specific responses to plasmid carriage were transcriptional changes of genes on putative prophage or foreign DNA regions. The extent of the impacts in host phenotypes and transcriptomes was similarly the largest in KT2440 and the lowest in Pf0-1. The host alterations controlled by pCAR1 carriage are important for understanding the fate of the plasmid and its host, plasmid maintenance, expression of plasmid genes, the host cell physiology, and host survivability in the environment. The growth-dependent change of chromosomal RNA maps from exponential to early stationary phases of pCAR1-harboring KT2440 and non-pCAR1 harboring KT2440 were compared. The growth-dependent change of chromosomal RNA maps from exponential to early stationary phases of pCAR1-harboring PAO1 and non-pCAR1 harboring PAO1 were compared. The growth-dependent change of chromosomal RNA maps from exponential to early stationary phases of pCAR1-harboring Pf0-1 and non-pCAR1 harboring Pf0-1 were compared. The growth-dependent change of RNA maps from exponential to early stationary phases of plasmid pCAR1possessed by 3 kinds of hosts were compared.

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Different resource allocation in a Bacillus subtilis population displaying bimodal motility

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