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- The cytoplasmic loops of AgrC contribute to the quorum-sensing activity of Staphylococcus aureus
- Qian Huang , Yihui Xie , Ziyu Yang , Danhong Cheng , Lei He , Hua Wang , Qian Liu , Min Li
- J. Microbiol. 2021;59(1):92-100. Published online November 17, 2020
- DOI: https://doi.org/10.1007/s12275-021-0274-x
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Abstract
- In Staphylococcus aureus, the accessory gene regulator (agr) quorum-sensing system is thought to play an important role in biofilm formation. The histidine kinase AgrC is one of the agr system components and activated by the self-generated auto-inducing peptide (AIP), which is released continuously into the extracellular environment during bacterial growth. The extracellular loops (Extra-loops) of AgrC are crucial for AIP binding. Here, we reported that the cytoplasmic loops (Cyto-loops) of AgrC are also involved in Agr activity. We identified S. aureus ST398 clinical isolates containing a naturally occurring single amino acid substitution (lysine to isoleucine) at position 73 of an AgrC Cyto-loop that exhibited significantly stronger biofilm formation and decreased Agr activity compared to the wild-type strain. A constructed strain containing the K73I point mutation in AgrC Cyto-loop continued to show a growth dependent induction of the agr system, although the growth dependent induction was delayed by about 6 h compared to the wild-type. In addition, a series of strains containing deletion mutants of the AgrC Cyto- and Extra-loops were constructed and revealed that the removal of the two Cyto-loops and Extra-loops 2 and 3 totally abolished the Agr activity and the growth-dependence on the agr system induction. Remarkably, the Extra-loop 1 deletion did not affect the Agr activity. In conclusion, the AgrC Cyto-loops play a crucial role in the S. aureus quorum-sensing activity.
Retracted Publication
- Cryptic prophages in a blaNDM-1-bearing plasmid increase bacterial survival against high NaCl concentration, high and low temperatures, and oxidative and immunological stressors
- So Yeon Kim , Kwan Soo Ko
- J. Microbiol. 2020;58(6):483-488. Published online March 28, 2020
- DOI: https://doi.org/10.1007/s12275-020-9605-6
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Abstract
- In this study, we investigated the effect of cryptic prophage regions in a blaNDM-1-bearing plasmid, which was identified in a patient from South Korea, on the survival of bacteria against adverse environmental conditions. First, we conjugated the intact plasmid and plasmids with deleted cryptic prophages into Escherichia coli DH5α. The E. coli transconjugants carrying the plasmid with intact cryptic prophages showed increased survival during treatment with a high concentration of NaCl, high and low temperatures, an oxidative stressor (H2O2), and an immunological stressor (human serum). By contrast, the transconjugants carrying the plasmid with a single-cryptic prophage knockout did not show any change in survival rates. mRNA expression analyses revealed that the genes encoding sigma factor proteins were highly upregulated by the tested stressors and affected the expression of various proteins (antioxidant, cell osmosis-related, heat shock, cold shock, and universal stress proteins) associated with the specific defense against each stress. These findings indicate that a bacterial strain carrying a plasmid with intact carbapenemase gene and cryptic prophage regions exhibited an increased resistance against simulated environmental stresses, and cryptic prophages in the plasmid might contribute to this enhanced stress resistance. Our study indicated that the coselection of antibiotic resistance and resistance to other stresses may help bacteria to increase survival rates against adverse environments and disseminate.
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