Bacillus subtilis two component system YvfT-YvfU is involved in thermal regulation of the ABC transporter YvfRS

FERNÁNDEZ, P; PORRINI, L; ALBANESI, D; DE MENDOZA, D; MANSILLA, MC

Congreso; IX Congreso Argentino de Microbiología General; 2013

SAMIGE

Bacteria can encounter a wide range of environments and must adapt to new conditions in order tosurvive. As the selective barrier between living cells and their environment, the plasma membraneplays a key role in cell viability. The barrier function of the cytoplasmic membrane is known to dependcritically on the physical state of lipid bilayers, making it susceptible to changes in environmentaltemperature. For signal transduction across the cell membrane, bacteria extensively usetwo-component systems (TCS), which have an input-sensing domain (histidine kinase, HK) and anoutput effector domain (response regulator, RR). The Des circuit of the Gram-positive bacteria Bacillussubtilis regulates the expression at low temperature of the fatty acid desaturase encoded by the desgene. It is composed by an autophosphorylatable HK (DesK), and a DNA binding RR (DesR). It hasrecently been demostrated that overexpression of DesR in B.subtilis desK null mutants results not onlyin the induction of the des gene but also of an operon formed by the genes yvfRSTU, which encodes aputative ABC transporter and a two component system. The bioinformatic analysis of YvfT-YvfUsequence showed a high identity with DesK-DesR. In adittion, the inverted repeated boxes in thepromoter region of yvfR are very similar to that of the regulatory region of the des promoter.In this work, we investigated whether YvfTU mediates activation of the ABC transporter YvfRS. Weperformed b-galactosidase assays of B.subtilis yvfTU null mutants carrying a transcriptional fusion ofPyvfR to lacZ (CM49). We found that transcription from PyvfR is activated only if YvfTU is expressedin trans, indicating that this TCS is essential for regulation of the transporter expression. Besides, suchexpression occurs at 37°C and not at 25°C. We also observed that YvfTU expression from aninducible promoter recovers the ability of a DesKR¯ mutant to express the des gene at lowtemperature, which implies an opposite behavior to the one seen with PyvfR.We also found that transcription of yvfR in CM49 is also activated when the regulator YvfU isexpressed in trans, but not by YvfT alone. Surprisingly, this expression depends on the presence ofDesR. To know whether YvfU induces yvfR operon in its unphosphorylated form or if it ought to bephosphorylated by DesK, we constructed a B. subtilis yvfTU null mutant that also is DesK¯, carryingthe transcriptional fusion PyvfR-lacZ.We can conclude that the ABC transporter YvfRS is regulated by the TCS YvfTU, in athermal-dependent fashion (activated at 37°C and not at 25°C). For the transcriptional activation ofthe yvfR gene, an interaction between both systems, DesKR and YvfTU is required. The differentbehavior of YvfR on Pdes and PyvfR might be explained by slight differences between the sequencesof regulator-binding regions in each promoter.