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Unravelling the complexity and redundancy of carbon catabolic repression in Pseudomonas fluorescens SBW25
Author(s) -
Liu Yunhao,
Gokhale Chaitanya S.,
Rainey Paul B.,
Zhang XueXian
Publication year - 2017
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13720
Subject(s) - pseudomonas fluorescens , biology , catabolism , psychological repression , redundancy (engineering) , carbon source , pseudomonas , microbiology and biotechnology , pseudomonadales , biochemistry , bacteria , genetics , metabolism , gene , engineering , gene expression , reliability engineering
Summary The two‐component system CbrAB is the principal regulator for cellular metabolic balance in Pseudomonas fluorescens SBW25 and is necessary for growth on many substrates including xylose. To understand the regulatory linkage between CbrAB and genes for xylose utilization ( xut ), we performed transposon mutagenesis of Δ cbrB to select for Xut + suppressors. This led to identification of crc and hfq . Subsequent genetic and biochemical analysis showed that Crc and Hfq are key mediators of succinate‐provoked carbon catabolite repression (CCR). Specifically, Crc/Hfq sequentially bind to mRNAs of both the transcriptional activator and structural genes involved in xylose catabolism. However, in the absence of succinate, repression is relieved through competitive binding by two ncRNAs, CrcY and CrcZ, whose expression is activated by CbrAB. These findings provoke a model for CCR in which it is assumed that crc and hfq are functionally complementary, whereas crcY and crcZ are genetically redundant. Inactivation of either crcY or crcZ produced no effects on bacterial fitness in laboratory media, however, results of mathematical modelling predict that the co‐existence of crcY and crcZ requires separate functional identity. Finally, we provide empirical evidence that CCR is advantageous in nutrient‐complex environments where preferred carbon sources are present at high concentrations but fluctuate in their availability.