Klebsiella pneumoniae type VI secretion system-mediated microbial competition is PhoPQ controlled and reactive oxygen species dependent

Abstract

Klebsiella pneumoniae is recognized as an urgent threat to human health due to the increasing isolation of multidrug resistant strains. Hypervirulent strains are a major concern due to their ability to cause life-threating infections in healthy hosts. The type VI secretion system (T6SS) is widely implicated in microbial antagonism, and it mediates interactions with host eukaryotic cells in some cases. In silico search for genes orthologous to T6SS component genes and T6SS effector genes across 700 K. pneumoniae genomes shows extensive diversity in T6SS genes across the K. pneumoniae species. Temperature, oxygen tension, pH, osmolarity, iron levels, and NaCl regulate the expression of the T6SS encoded by a hypervirulent K. pneumoniae strain. Polymyxins and human defensin 3 also increase the activity of the T6SS. A screen for regulators governing T6SS uncover the correlation between the transcription of the T6SS and the ability to kill E. coli prey. Whereas H-NS represses the T6SS, PhoPQ, PmrAB, Hfq, Fur, RpoS and RpoN positively regulate the T6SS. K. pneumoniae T6SS mediates intra and inter species bacterial competition. This antagonism is only evident when the prey possesses an active T6SS. The PhoPQ two component system governs the activation of K. pneumoniae T6SS in bacterial competitions. Mechanistically, PhoQ periplasmic domain, and the acid patch within, is essential to activate K. pneumoniae T6SS. Klebsiella T6SS also mediates anti-fungal competition. We have delineated the contribution of each of the individual VgrGs in microbial competition and identified VgrG4 as a T6SS effector. The DUF2345 domain of VgrG4 is sufficient to intoxicate bacteria and yeast. ROS generation mediates the antibacterial effects of VgrG4, and the antitoxin Sel1E protects against the toxic activity of VgrG4. Our findings provide a better understanding of the regulation of the T6SS in bacterial competitions, and place ROS as an early event in microbial competition.

Virulence Factors in Hypervirulent Klebsiella pneumoniae

“…Although >25% Gram-negative bacteria encode T6SSs, wild-type NTUH-2044 has been confirmed to outcompete Salmonella Typhimurium, E. coli, and T6SS-null K. pneumoniae in a T6SS-dependent manner, and the frequency of T6SSs in KLA strains is significantly higher compared to that in the intestinal-colonizing strains, suggesting that T6SSs may confer an advantage for hvKP survival (Clemens et al, 2018;Hsieh et al, 2019). Another study reported that in bacterial competition, K. pneumoniae T6SSs were activated by the PhoPQ system, followed by the use of effectors to kill E. coli prey that lack T6SS immunity genes (Storey et al, 2020). Moreover, the overexpression of a T6SS effector in the carbapenemaseproducing K. pneumoniae strain, the phospholipase Tle1, was found to inhibit the growth of E. coli (Liu et al, 2017).…”

Activity, delivery, and diversity of Type VI secretion effectors

“…DUF2345 domains can perform additional functions. In Acinetobacter baumannii , the DUF2345 of VgrG is essential for T6SS assembly, while the VgrG4 DUF2345 domain of Klebsiella pneumoniae is itself an antibacterial and antifungal toxic effector inducing response to reactive oxygen species (Lopez et al, 2020; Storey et al, 2020). Rhs are large proteins that were first identified as recombination‐prone loci in chromosomes (Lin et al, 1984).…”

The Acquisition of Colistin Resistance Is Associated to the Amplification of a Large Chromosomal Region in Klebsiella pneumoniae kp52145

“…The strain K. pneumoniae kp52145 [ 31 ], also known as CIP52.145 [ 32 ], belongs to the K. pneumoniae KpI group that includes the majority of strains associated with human infection, including several multidrug-resistant and hypervirulent clones [ 33 ]. It is then a good model for searching for novel potential mechanisms of antibiotic resistance.…”