Klebsiella pneumoniaetype 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 possess 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. Structurally, domain DUF2345 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.AUTHOR SUMMARYKlebsiella pneumoniae has been singled out as an “urgent threat to human health” due to extremely drug resistant strains. Numerous studies investigate the molecular mechanisms underlying antibiotic resistance in K. pneumoniae, while others dissect the virulence strategies of this pathogen. However, there is still limited knowledge on the fitness of Klebsiella in the environment, and particularly the competition of Klebsiella with other species. Here, we demonstrated that Klebsiella exploits the type VI secretion system (T6SS) nanoweapon to kill bacterial competitors and fungi. K. pneumoniae perceives T6SS attacks from bacterial competitors, resulting in retaliation against the aggressive cell. The perception of the attack involved the sensor PhoPQ and led to the up-regulation of the T6SS. We identified one of the toxins deployed by the T6SS to antagonize other microbes, and revealed how Klebsiella protects itself from this toxin. Our findings provide a better understanding of the T6SS role in microbial competition and uncover new aspects on how bacteria regulate T6SS-mediated microbial antagonism.

The evolution of tit-for-tat in bacteria via the type VI secretion system

“…3e), because it provides cells with additional information on the location of attackers. This contrasts with other forms of T6SS regulation, where the rate of T6SS firing is increased in response to cellular damage 18,24,58 , but with T6SS placement occurring apparently at random. By placing T6SS assemblies at attack sites, P. aeruginosa can substantially improve its hit efficiency, compared with a random firer that has no information on the location of its target.…”

Antieukaryotic Type Six Secretion System Virulence Factors of Bacteria

“…26 This study showed that VgrG4, and not VgrG2, is a virulence determinant responsible for the antifungal action of T6SS against both yeasts, indicating that vgrG4 could be a frequently used T6SS antifungal factor in K. pneumoniae strains; in quantitative killing assays with C. albicans, vgrG2 or vgrG4 mutant strains did not subvert cell growth, whereas with S. cerevisiae, cell growth was not impaired in the presence of vgrG4 mutant growth. 26 Therefore, we are likely to see unparalleled insights into the function of T6SS antifungal factors and a compendium of target fungi with the support of current resources, including bioinformatics approaches, as discussed below. In the future, these insights will guide the use of these bacterial T6SS factors as antifungals to treat fungal infections in animals and plants.…”

Roles of the Hcp family proteins in the pathogenicity of Salmonella typhimurium 14028s

“…This can be explained by the data from qRT-PCR, which showed that in Δhcp1 mutant the type 2 flagellar gene fliA and type 3 flagellar genes fliC and fljB all showed significant decreased transcriptions, which may result in reduced synthesis of flagellin and thus influence the motility. Previous studies [33,34] have found that rpoS can regulate the expression of T6SS to help bacteria survive under stress conditions, another study [35] also found that it can be regulated by T6SS. In this study, we found the deletion of hcp can affect the transcription of rpoS.…”