Biology subjects

Bowring, J. Z.

Publications and source records attributed to Bowring, J. Z..

3 recordsLinked to original sources

bioRxiv2023

Cross-species communication via agr controls phage susceptibility in Staphylococcus aureus

Bacteria and their viruses (phages) use quorum sensing (QS) systems to coordinate group behavior. In Staphylococcus aureus, QS plays a critical role in the transition from colonization to infection and involves the accumulation of auto-inducing peptides (AIPs). Humans and animals are also colonized by non-aureus staphylococci (NAS) that produce AIPs, many of which inhibit S. aureus QS. We found that QS induction is necessary for S. aureus susceptibility to the lytic phage, Stab20 and that in mixed communities with NAS producing inhibitory AIPs, S. aureus is protected from phage infection. The primary phage receptors in S. aureus are wall teichoic acids (WTA) substituted with - and/or {beta}-linked N- acetylglucosamine (GlcNAc). We show that QS induction reduces -GlcNAc substitutions and enables Stab20 infection through binding to {beta}-glycosylated WTA. However, in the presence of inhibitory AIPs or during co-culture with NAS, QS induction and Stab20 infection are impeded. Our results highlight how cross-species communication can significantly impact bacterial susceptibility to phages and may explain occasional failures observed when phages are used as antimicrobials in for example phage therapy.

microbiology↗

bioRxiv2023

Endogenous Staphylococcus aureus CRISPR-cas system limits phage proliferation and efficiently excises from the genome as part of the SCCmec cassette

CRISPR-Cas is an adaptive immune system that allows bacteria to inactivate mobile genetic elements. Approximately 50% of bacteria harbor CRISPR-cas, however in the human pathogen Staphylococcus aureus, CRISPR-cas loci are less common and often studied in heterologous systems. We analyzed the prevalence of CRISPR-cas in genomes of methicillin resistant Staphylococcus aureus (MRSA) isolated in Denmark. Only 2.9 % of the strains carried CRISPR-cas systems, but for strains of sequence type ST630 over half were positive. All CRISPR-cas loci were type III-A and located within the staphylococcal chromosomal cassette (SCCmec) type V(5C2&5) conferring {beta}-lactam resistance. Curiously, only 23 different CRISPR spacers were identified in 69 CRISPR-positive strains and almost identical SCCmec cassettes, CRISPR arrays and cas genes, are present in staphylococcal species other than aureus, suggesting that these were transferred horizontally. For the ST630 strain 110900, we demonstrate that the SCCmec cassette containing CRISPR-cas excises from the chromosome at high frequency. However, the cassette was not transferable under the conditions investigated. One of the CRISPR spacers targets a late gene in the lytic bacteriophage (phage) virus philPLA-RODI, and we show that the system protects against phage infection by reducing phage burst size. However, CRISPR-Cas can be overloaded or bypassed by CRISPR escape mutants. Our results imply that the endogenous type III-A CRISPR-Cas system in S. aureus is active against targeted phages, albeit with low efficacy. This suggests native S. aureus CRISPR-Cas offers only partial immunity, and in nature may work in tandem with other defense systems. ImportanceCRISPR-Cas is an adaptive immune system enabling bacteria and archaea to protect themselves against mobile genetic elements such as phages. In strains of Staphylococcus aureus, CRISPR-cas is rare, but when present, it is located within the SCCmec element encoding resistance to methicillin and other {beta}-lactam antibiotics. We show that the entire module is excisable, with almost identical versions found in different species of non-aureus staphylococci suggesting that the system only rarely acquires new spacers in S. aureus. Additionally, we show that in its endogenous form, the S. aureus CRISPR-Cas is active but inefficient against lytic phages, with phages being able to form escape mutants or overload the system. This leads us to propose that CRISPR-Cas in S. aureus offers only partial immunity in native systems, and so may work together with other defense systems to prevent phage-mediated killing.

microbiology↗

bioRxiv2020

Screening for highly transduced genes in Staphylococcus aureus reveals both lateral and specialized transduction

Bacteriophage-mediated transduction of bacterial DNA is a major route of horizontal gene transfer in the human pathogen, Staphylococcus aureus. Transduction involves packaging of bacterial DNA by viruses and enables transmission of virulence and resistance genes between cells. To learn more about transduction in S. aureus, we searched a transposon mutant library for genes and mutations that enhanced transfer mediated by the temperate phage, {varphi}11. Using a novel screening strategy, we performed multiple rounds of transduction of transposon mutant pools selecting for an antibiotic resistance marker within the transposon element. When determining the locations of transferred mutations, we found that, within each pool of 96 mutants the screen had selected for just 1 or 2 transposon mutant(s). Subsequent analysis showed that the position of the transposon, rather than inactivation of bacterial genes, was responsible for the phenotype. Interestingly, from multiple rounds we identified a pattern of transduction that encompassed mobile genetic elements, as well as chromosomal regions both upstream and downstream of the phage integration site. The latter was confirmed by DNA sequencing of purified phage lysates. Importantly, transduction frequencies were lower for phage lysates obtained by phage infection rather than induction. Our results confirm previous reports of lateral transduction of bacterial DNA downstream of the integrated phage, but also indicate specialized transduction of DNA upstream of the phage, likely involving imprecise excision of the phage from the bacterial genome. These findings illustrate the complexity of transduction processes and increase our understanding of the mechanisms by which phages transfer bacterial DNA. ImportanceHorizontal transfer of DNA between bacterial cells contributes to the spread of virulence and antibiotic resistance genes in human pathogens. For Staphylococcus aureus, bacterial viruses are particularly important. These viruses, termed bacteriophages, can transfer bacterial DNA between cells by a process known as transduction, which despite of its importance is only poorly characterized. Here, we employed a transposon mutant library to investigate transduction in S. aureus. We show that the location of bacterial DNA in relation to bacteriophages integrated in the bacterial genome is a key decider of how frequently that DNA is transduced. Based on serial transduction of transposon mutant pools and direct sequencing of bacterial DNA in bacteriophage particles, we demonstrate both lateral and specialized transduction. The use of mutant libraries to investigate the patterns of bacterial DNA transfer between cells could help understand how bacteria evolve virulence and resistance and may ultimately lead to new intervention strategies.

microbiology↗