Two models for <i>B</i>. <i>cereus clhAB</i>_<i>2</i> regulation.

<p>Left: regulation of <i>clhAB</i>_<i>2</i> expression in an amino acid- rich medium. In a nutrient-rich medium (such as LB medium [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.ref013" target="_blank">13</a>]), ILV uptake is sufficient to maintain the endogenous pool of ILV. The CodY global regulatory protein displays enhanced affinity for its DNA target when bound to ILV[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.ref027" target="_blank">27</a>]. ILV-bound CodY binds to the CodY binding sequence upstream of <i>clhAB</i>_<i>2</i> and assists RNA polymerase with transcribing the <i>clhAB</i>_<i>2</i> operon (Figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.g003" target="_blank">3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.g004" target="_blank">4</a>). The expression level of <i>clhAB</i>_<i>2</i> is constant and moderate (i.e. basal level) during the late exponential and transition growth phases (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.g001" target="_blank">Fig 1</a>). Right: regulation of <i>clhAB</i>_<i>2</i> expression in an amino acid- glucose- rich medium. In LB medium with 0.35% glucose, ILV-CodY binds to the CodY motif and activates <i>clhAB</i>_<i>2</i> expression, but the expression profile is different (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.g001" target="_blank">Fig 1</a>). CcpA plays a positive role by indirectly regulating the transcription of <i>clhAB</i>_<i>2</i> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.g002" target="_blank">Fig 2</a>) and this regulatory pathway remains to be characterized. The role of known or hypothetical effector molecules is depicted with a dashed arrow. In the left part, the ILV effector [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.ref027" target="_blank">27</a>] is depicted with a green dashed arrow; in right part, the Fru-6-P [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184975#pone.0184975.ref025" target="_blank">25</a>] and unknown glycolytic intermediate effectors are depicted with blue dashed arrows. Moderate and constant <i>clhAB</i>_<i>2</i> expression is depicted by three identical gray arrows. High and gradual <i>clhAB</i>_<i>2</i> expression is depicted by three non-identical gray arrows. The intracellular ILV pool is depicted as a green box. The CodY motif sequence is depicted as a red box. The unknown DNA-binding motif is depicted as a blue box.?, unknown CcpA-dependent signaling pathway; ?, unknown transcriptional regulator. Fru-6-P, fructose-6-phosphate, Glc-6-P, glucose-6-phosphate. ILV, isoleucine, leucine, valine. CodY, CodY transcriptional regulator. CcpA, CcpA global carbon regulator; PTS, phosphotransferase system. T, unknown transporter of ILV.