Biology subjects

Dandekar, A. A.

Publications and source records attributed to Dandekar, A. A..

3 recordsLinked to original sources

bioRxiv2020

Tobramycin adaptation enhances policing of social cheaters in Pseudomonas aeruginosa

The Pseudomonas aeruginosa LasR-I quorum sensing (QS) system regulates secreted proteases that can be exploited by cheaters, such as QS receptor-defective (lasR) mutants. lasR mutants emerge in populations growing on casein as a sole source of carbon and energy and increase in the population because they do not incur the substantial cost of engaging in QS. QS also increases resistance to some antibiotics, such as tobramycin. Here, we show that tobramycin suppresses the emergence of lasR mutants in casein-passaged populations. We also identify several mutations that accumulate in those populations indicating evidence of antibiotic adaptation. Mutations in one gene, ptsP, increase activity of the LasR-I system and production of a QS-controlled phenazine, pyocyanin. We find that mutations in ptsP lead to suppression of cheaters independent of tobramycin. Cheater suppression relies on pyocyanin, which acts as a policing toxin by targeting cheaters. These results show that tobramycin suppresses lasR mutants through two mechanisms: first, by directly acting on tobramycin-susceptible cheaters and second, by selecting mutations in ptsP that lead to pyocyanin-dependent policing. This work demonstrates how adaptive mutations can alter the dynamics of cooperator-cheater relationships, which might be important for populations adapting to antibiotics during infections.

microbiology↗

bioRxiv2020

Burkholderia thailandensis methylated hydroxy-alkylquinolines: biosynthesis and antimicrobial activity in co-culture experiments

The bacterium Burkholderia thailandensis produces an arsenal of secondary metabolites that have diverse structures and roles in the ecology of this soil-dwelling bacterium. In liquid co-culture experiments, B. thailandensis secretes an antimicrobial that nearly eliminates another soil bacterium, Bacillus subtilis. To identify the antimicrobial, we used a transposon mutagenesis approach. This screen identified antimicrobial-defective mutants with insertions in the hmqA, hmqC and hmqF genes involved in biosynthesis of a family of 2-alkyl-4(1H)-quinolones called 4-hydroxy-3-methyl-2-alkenylquinolines (HMAQs), which are closely related to the Pseudomonas aeruginosa 4-hydroxy-2-alkylquinolines (HAQs). Insertions also occurred in the previously uncharacterized gene BTH_II1576. Results confirm that BTH_II1576 is involved in generating N-oxide derivatives of HMAQs (HMAQ-NO) in B. thailandensis and that HMAQ-NOs are sufficient to eliminate B. subtilis in co-cultures. Moreover, synthetic HMAQ-NO is [~]50-fold more active than HMAQ. Both the methyl group and the length of the carbon side chain account for high activity of HMAQ-NO against B. subtilis. The results provide new information on the biosynthesis and activities of HMAQs and reveal new insight into how these molecules might be important for the ecology of B. thailandensis. IMPORTANCEThe soil bacterium Burkholderia thailandensis produces 2-alkyl-4(1H)-quinolones, mostly methylated 4-hydroxy-alkenylquinolines, a family of relatively unstudied metabolites similar to molecules also synthesized by Pseudomonas aeruginosa. Several of the methylated 4-hydroxy-alkenylquinolines have antimicrobial activity against other species. We show that N-oxidated methyl-alkenylquinolines are particularly antimicrobial and sufficient to kill Bacillus subtilis in co-cultures. We confirmed their biosynthesis requires the previously unstudied protein HmqL. These results provide new information about the biology of 2-alkyl-4(1H)-quinolones, particularly the methylated 4-hydroxy-alkenylquinolines, which are unique to B. thailandensis. This study also has importance for understanding B. thailandensis secondary metabolites and has implications for potential therapeutic development.

microbiology↗

bioRxiv2019

Non-hierarchical, RhlR-regulated acyl-homoserine lactone quorum sensing in a cystic fibrosis isolate of Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa is a leading cause of airway infection in cystic fibrosis (CF) patients. P. aeruginosa employs several hierarchically arranged and interconnected quorum sensing (QS) regulatory circuits to produce a battery of virulence factors such as elastase, phenazines, and rhamnolipids. The QS transcription factor LasR sits atop this hierarchy, and activates the transcription of dozens of genes, including that encoding the QS regulator RhlR. Paradoxically, inactivating lasR mutations are frequently observed in isolates from CF patients with chronic P. aeruginosa infections. In contrast, mutations in rhlR are rare. We have recently shown that in CF isolates, the QS circuitry is often \"rewired\" such that RhlR acts in a LasR-independent manner. To begin understanding how QS activity differs in this \"rewired\" background, we characterized QS activation and RhlR-regulated gene expression in P. aeruginosa E90, a LasR-null, RhlR-active chronic infection isolate. In this isolate, RhlR activates the expression of 53 genes in response to increasing cell density. The genes regulated by RhlR include several that encode virulence factors. Some, but not all, of these genes are present in the QS regulon described in the well-studied laboratory strain PAO1. We also demonstrate that E90 produces virulence factors at similar concentrations to that of PAO1. Unlike PAO1, cytotoxicity by E90 in a three-dimensional lung epithelium cell model is also RhlR-regulated. These data illuminate a \"rewired\" LasR-independent RhlR regulon in chronic infection isolates and suggest that RhlR may be a target for therapeutic development in chronic infections.\n\nAUTHOR SUMMARYPseudomonas aeruginosa is a prominent cystic fibrosis (CF) pathogen that uses quorum sensing (QS) to regulate virulence. In laboratory strains, the key QS regulator is LasR. Some isolates from patients with chronic CF infections appear to use an alternate QS circuitry in which another transcriptional regulator, RhlR, mediates QS. We show that a LasR-null CF clinical isolate engages in QS through RhlR and remains capable of inducing cell death in an in vivo-like lung epithelium cell model. Our findings support the notion that LasR-null clinical isolates can engage in RhlR QS and highlight the centrality of RhlR gene regulation in chronic P. aeruginosa infections.

microbiology↗