Biology subjects

Hoyland-Kroghsbo, N. M.

Publications and source records attributed to Hoyland-Kroghsbo, N. M..

3 recordsLinked to original sources

bioRxiv2023

The great divide: rhamnolipids mediate separation between P. aeruginosa and S. aureus

The coexistence of multiple bacterial species during infection can have significant impacts on pathogenesis. Pseudomonas aeruginosa and Staphylococcus aureus are opportunistic bacterial pathogens that can co-infect hosts and cause serious illness. The factors that dictate whether one species will outcompete the other or whether the two species can coexist are not fully understood. We investigated the role of surfactants in the interactions between these two species on a surface that enables P. aeruginosa to swarm. We found that P. aeruginosa swarms are repelled by colonies of clinical S. aureus isolates, creating physical separation between the two strains. This effect was abolished in mutants of S. aureus that were defective in the production of phenol-soluble modulins (PSMs), which form amyloid fibrils around wild-type colonies. We investigated the mechanism that establishes physical separation between the two species using the Imaging of Reflected Illuminated Structures (IRIS) method, which tracks the flow of the rhamnolipid surfactant layer produced by P. aeruginosa. We found that PSMs produced by S. aureus deflected the rhamnolipid surfactant layer flow, which in turn, altered the direction of P. aeruginosa swarms. These findings show that rhamnolipids mediate physical separation between P. aeruginosa and S. aureus, which enables these species to coexist in distinct microenvironments. Additionally, we found that a Bacillus subtilis surfactant and abiotic hydrophobic molecules repelled P. aeruginosa swarms through surfactant deflection. Our results suggest that surfactant interactions could have major impacts on bacteria-bacteria and bacteria-host relationships. In addition, our findings uncover a mechanism responsible for P. aeruginosa swarm development that does not rely on sensing but instead is guided largely by the flow of the surfactant layer and its boundaries.

microbiology↗

bioRxiv2023

Quorum sensing inhibits Type III-A CRISPR-Cas system activity through repressing positive regulators SarA and ArcR in Staphylococcus aureus

CRISPR-Cas is an adaptive immune system that protects prokaryotes from the invasion of foreign genetic elements. The components and immunity mechanisms of CRISPR-Cas have been extensively studied, but the regulation of this system in Staphylococci remains unclear. Here, we show that in the S. aureus Type III-A CRISPR-Cas system, the Pcas of 300 bp located in cas1 displays as a critical regulatory node that initiates the transcription of cas gene clusters. We discovered two transcriptional regulators, SarA and CRP-like ArcR, promote the expression and activity of the CRISPR-Cas system by directly binding to the novel promoter Pcas. Furthermore, we demonstrated that the cell-cell communication, known as quorum sensing (QS), inhibits the activity of CRISPR-Cas system by repressing the positive regulators SarA and ArcR. Bioinformatic analyses suggest that Pcas is conserved in many Type II and III CRISPR-Cas systems in Firmicutes. Our data reveal a new regulatory mechanism for QS-mediated repression of the Type III-A CRISPR-Cas system, which may allow S. aureus to acquire foreign genetic elements encoding antibiotic resistance or virulence factors specifically at high cell density.

microbiology↗

bioRxiv2021

Phage infection restores PQS signaling and enhances growth of a Pseudomonas aeruginosa lasI quorum-sensing mutant

Bacteriophage (phage) therapy is reemerging as a valuable tool to combat multidrug resistant bacteria. A major hurdle in developing efficacious bacteriophage therapies is that bacteria acquire resistance to phage killing. In this context, it is noteworthy that quorum sensing (QS), the bacterial cell-to-cell communication mechanism that promotes collective undertaking of group behaviors including anti-phage defenses, enhances bacterial survival in the face of phage attack. QS relies on the production, release, accumulation, and detection of signal molecules called autoinducers. In the opportunistic pathogen Pseudomonas aeruginosa, the LasI/R QS system induces the RhlI/R QS system, and these two systems control, in opposing manners, the PQS QS system that relies on the autoinducer called PQS. A {Delta}lasI mutant is impaired in PQS synthesis, leading to accumulation of the precursor molecule HHQ. HHQ suppresses growth of the P. aeruginosa {Delta}lasI strain. We uncover a phage infection-induced mechanism that restores expression of the pqsH gene in the P. aeruginosa {Delta}lasI QS mutant. PqsH converts HHQ into PQS, preventing HHQ-mediated growth inhibition. Thus, phage-infected P. aeruginosa {Delta}lasI cells exhibit superior growth compared to uninfected cells. Phage infection also restores expression of virulence factors and the CRISPR-cas anti-phage defense system in the P. aeruginosa {Delta}lasI strain. This study highlights a challenge for phage therapy, namely that phage infection may make particular bacterial strains faster growing, more virulent, and resistant to phage killing. ImportanceThe emergence of multidrug resistant bacteria necessitates development of new antimicrobial therapies. Phage therapy relies on exploiting phages, natural enemies of bacteria, in the fight against pathogenic bacteria. For successful phage therapy development, potent phages that exhibit low propensity for acquisition of bacterial resistance are desired. Here, we show that phage infection restores QS, a cell-to-cell communication mechanism in a P. aeruginosa QS mutant, which increases its virulence and resistance to phage killing. Importantly, clinical isolates of P. aeruginosa frequently harbor mutations in particular QS genes. Thus, phage therapies against such P. aeruginosa strains may inadvertently increase bacterial virulence. Our study underscores the importance of characterizing phage-host interactions in the context of bacterial mutants that are relevant in clinical settings prior to selecting phages for therapy.

microbiology↗