Phase-variable expression of pdcB, a phosphodiesterase, influences sporulation in Clostridioides difficile.
Phase-variable expression of pdcB, a phosphodiesterase, influences sporulation in Clostridioides difficile.
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DOI：
10.1111/mmi.14828
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发表时间：
2021-11
影响因子：
3.6
通讯作者：
Govind R
中科院分区：
文献类型：
--
作者：
Dhungel BA;Govind R
Clostridioides difficile is the causative agent of antibiotic-associated diarrhea and is the leading cause of nosocomial infection in developed countries. An increasing number of C. difficile infections are attributed to epidemic strains that produce more toxins and spores. C. difficile spores are the major factor for the transmission and persistence of the organism. Previous studies have identified global regulators that influence sporulation in C. difficile. This study discovers that PdcB, a phosphodiesterase, enhances sporulation in C. difficile strain UK1. Through genetic and biochemical assays, we show that phase-variable expression of pdcB results in hypo- and hyper-sporulation phenotypes. In the “ON” orientation, the identified promotor is in the right orientation to drive the expression of pdcB. Production of the PdcB phosphodiesterase reduces the intracellular cyclic-di-GMP concentration, resulting in a hyper-sporulation phenotype. Loss of PdcB due to the pdcB promoter being in the OFF orientation or mutation of pdcB results in increased cyclic-di-GMP levels and a hypo-sporulation phenotype. Additionally, we demonstrate that CodY binds to the upstream region of pdcB. DNA inversion reorients the CodY binding site so that in the OFF orientation, CodY binds a site that is upstream of the pdcB promoter and can further repress gene expression. In UK_T translucent cells (pdcB-OFF), the predicted promoter region of pdcB is in the inverted orientation. The binding of CodY downstream further blocks any transcription of the pdcB. In the UK_O opaque cells (pdcB-ON), because of the DNA inversion, the predicted promoter is in the right orientation and drives the expression of pdcB, and is also not affected by the CodY binding to the upstream. Increased production of PdcB results in decreased c-di-GMP, which in turn influences the sporulation rate. In the C. difficile UK1 strain, phase variation resulted in two distinct colony morphologies: transparent UK T cells and opaque UK O cells. Whole-genome sequencing of UK_T and UK_O revealed that they differ in the orientation of the DNA sequence upstream of pdcB, which codes for a phosphodiesterase. In UK_T cells, the predicted promoter region of pdcB is in the inverted orientation. The binding of CodY downstream further blocks any transcription of pdcB. In UK O cells, the predicted promoter is in an orientation that promotes the expression of pdcB and is unaffected by CodY binding to the upstream region. Increased production of PdcB results in decreased c-di-GMP, which in turn influences sporulation through a mechanism yet to be discovered.
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