The histone-like protein AlgP regulon is distinct in mucoid and nonmucoid Pseudomonas aeruginosa and does not include alginate biosynthesis genes

Abstract

<jats:p>The opportunistic bacterial pathogen <jats:italic> <jats:named-content content-type="species"> <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://doi.org/10.1601/nm.2553" xlink:type="simple">Pseudomonas aeruginosa</jats:ext-link> </jats:named-content> </jats:italic> causes acute and chronic infections that are notoriously difficult to treat. In people with cystic fibrosis, <jats:italic> <jats:named-content content-type="species"> <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://doi.org/10.1601/nm.2553" xlink:type="simple">P. aeruginosa</jats:ext-link> </jats:named-content> </jats:italic> can cause lifelong lung infections, and isolation of mucoid <jats:italic> <jats:named-content content-type="species"> <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://doi.org/10.1601/nm.2553" xlink:type="simple">P. aeruginosa</jats:ext-link> </jats:named-content> </jats:italic>, resulting from the overproduction of alginate, is associated with chronic infection. The histone-like protein AlgP has previously been implicated in the control of alginate gene expression in mucoid strains, but this regulation is unclear. To explore AlgP in further detail, we deleted <jats:italic>algP</jats:italic> in mucoid strains and demonstrated that the deletion of <jats:italic>algP</jats:italic> did not result in a nonmucoid phenotype or a decrease in alginate production. We showed that the <jats:italic>algP</jats:italic> promoter is expressed by both the nonmucoid strain PAO1 and the isogenic mucoid strain PDO300, suggesting that there may be genes that are differentially regulated between these strains. In support of this, using RNA sequencing, we identified a small AlgP regulon that has no significant overlap between PAO1 and PDO300 and established that alginate genes were not differentially regulated by the deletion of <jats:italic>algP</jats:italic>. Of note, we found that deleting <jats:italic>algP</jats:italic> in PAO1 increased expression of the nitric oxide operon <jats:italic>norCBD</jats:italic> and the nitrous oxide reductase genes <jats:italic>nosRZ</jats:italic> and subsequently promoted growth of PAO1 under anaerobic conditions. Altogether, we have defined a narrow regulon of genes controlled by AlgP and provided evidence that alginate production is not greatly affected by AlgP, countering the long-standing premise in the field.</jats:p>

The Histone H1-like protein AlgP facilitates even spacing of polyphosphate granules in Pseudomonas aeruginosa

“…Our discovery that AlgP affects polyP granule localization demonstrates that this protein remains important for starvation physiology. Although our AlgP mutant does not display a defect in cell cycle exit, there are intriguing clues that it may play a role in modulating gene expression and affect anaerobic survival(30). Indeed, AlgP was identified as highly expressed in the metabolically less active regions of P. aeruginosa biofilms using BONCAT labeling, suggesting that starvation upregulates its expression(31).…”

“…In addition to the sequence homology to PhaF, AlgP has interesting similarities in terms of sequence composition to the intrinsically disordered C-terminal tail of eukaryotic histone H1, also rich in lysine, proline, and alanine, as has been previously noted (12,27,30). Unlike the other core histones which are thought to have evolved from archaea, the histone H1 family is thought to be of bacterial origin (38).…”

“…Recently, the putative role of AlgP in alginate biosynthesis in P. aeruginosa has been called into question with the observation that deletion of algP in two different mucoid strains of P. aeruginosa , did not result in a nonmucoid phenotype. In the Δ algP mutant, alginate production was not attenuated and the alginate biosynthetic operon was not affected(30). Our discovery that AlgP affects polyP granule localization demonstrates that this protein remains important for starvation physiology.…”

The Histone H1-Like Protein AlgP Facilitates Even Spacing of Polyphosphate Granules in Pseudomonas aeruginosa

“…Prior studies have demonstrated that this C-terminal domain is a mutational hot spot in clinical isolates of P. aeruginosa from the lungs of cystic fibrosis (CF) patients, raising the possibility that algP may be under selective pressure in chronic infections ( 15 , 16 ). The C-terminal domain of AlgP has also previously been noted for its similarities to eukaryotic histone H1, due to its enrichment in lysine, alanine and proline residues, intrinsic disorder, and the ability of C-terminally-derived peptides to bind to DNA ( 14 , 15 , 17 , 18 ). We found that the C-terminus of AlgP is required for granule spacing but that AlgP does not play a role in efficient cell cycle exit during nitrogen starvation.…”

Microbial Musings – September 2020

“…Finally, check out this month’s Editor’s Choice, selected by Senior Editor Gail Preston, concerning the function of the AlgP regulon in P. aeruginosa , from Ashley Cross ( @PresidentCross ) in the group of Joanna Goldberg at Emory University School of Medicine, USA with ex-Senior Editor Marvin Whiteley ( @whiteleylab ) [ 19 ]. And look out for our adverts for Editors, Senior Editors and our Deputy Editor in Chief – come and join us and help #publishingforthecommunity as we take the journal forward to its big celebration in 2022.…”