AUTHOR=Ogura Mitsuo , Shindo Kazutoshi , Kanesaki Yu 

TITLE=Bacillus subtilis Nucleoid-Associated Protein YlxR Is Involved in Bimodal Expression of the Fructoselysine Utilization Operon (frlBONMD-yurJ) Promoter

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.02024

DOI=10.3389/fmicb.2020.02024

ISSN=1664-302X

ABSTRACT=<p>Bacteria must survive harsh environmental fluctuations at times and have evolved several strategies. “Collective” behaviors have been identified due to recent progress in single-cell analysis. Since most bacteria exist as single cells, bacterial populations are often considered clonal. However, accumulated evidence suggests this is not the case. Gene expression and protein expression are often not homogeneous, resulting in phenotypic heterogeneity. In extreme cases, this leads to bistability, the existence of two stable states. In many cases, expression of key master regulators is bimodal via positive feedback loops causing bimodal expression of the target genes. We observed bimodal expression of metabolic genes for alternative carbon sources. Expression profiles of the <italic>frlBONMD-yurJ</italic> operon driven by the <italic>frlB</italic> promoter (P<italic>frlB</italic>), which encodes degradation enzymes and a transporter for amino sugars including fructoselysine, were investigated using transcriptional <italic>lacZ</italic> and <italic>gfp</italic>, and translational fluorescence reporter <italic>mCherry</italic> fusions. Disruption effects of genes encoding CodY, FrlR, RNaseY, and nucleoid-associated protein YlxR, four known regulatory factors for P<italic>frlB</italic>, were examined for expression of each fusion construct. Expression of P<italic>frlB-gfp</italic> and P<italic>frlB</italic>-<italic>mCherry</italic>, which were located at <italic>amyE</italic> and its original locus, respectively, was bimodal; and disruption of <italic>ylxR</italic> resulted in the disappearance of the clear bimodal expression pattern in flow cytometric analyses. This suggested a role for YlxR on the bimodal expression of P<italic>frlB</italic>. The data indicated that YlxR acted on the bimodal expression of P<italic>frlB</italic> through both transcription and translation. YlxR regulates many genes, including those related to translation, supporting the above notion. Depletion of RNaseY abolished heterogenous expression of transcriptional P<italic>frlB-gfp</italic> but not bimodal expression of translational P<italic>frlB</italic>-<italic>mCherry</italic>, suggesting the role of RNaseY in regulation of the operon through mRNA stability control and regulatory mechanism for P<italic>frlB</italic>-<italic>mCherry</italic> at the translational level. Based on these results, we discuss the meaning and possible cause of bimodal P<italic>frlB</italic> expression.</p>