Comprehensive identification of Vibrio vulnificus genes required for growth in human serum

Abstract

Vibrio vulnificus can be a highly invasive pathogen capable of spreading from an infection site to the bloodstream, causing sepsis and death. To survive and proliferate in blood, the pathogen requires mechanisms to overcome the innate immune defenses and metabolic limitations of this host niche. We created a high-density transposon mutant library in YJ016, a strain representative of the most virulent V. vulnificus lineage (or phylogroup) and used transposon insertion sequencing (TIS) screens to identify loci that enable the pathogen to survive and proliferate in human serum. Initially, genes underrepresented for insertions were used to estimate the V. vulnificus essential gene set; comparisons of these genes with similar TIS-based classification of underrepresented genes in other vibrios enabled the compilation of a common Vibrio essential gene set. Analysis of the relative abundance of insertion mutants in the library after exposure to serum suggested that genes involved in capsule biogenesis are critical for YJ016 complement resistance. Notably, homologues of two genes required for YJ016 serum-resistance and capsule biogenesis were not previously linked to capsule biogenesis and are largely absent from other V. vulnificus strains. The relative abundance of mutants after exposure to heat inactivated serum was compared with the findings from the serum screen. These comparisons suggest that in both conditions the pathogen relies on its Na+ transporting NADH-ubiquinone reductase (NQR) complex and type II secretion system to survive/proliferate within the metabolic constraints of serum. Collectively, our findings reveal the potency of comparative TIS screens to provide knowledge of how a pathogen overcomes the diverse limitations to growth imposed by serum.

Structural and functional characterization of a modified legionaminic acid involved in glycosylation of a bacterial lipopolysaccharide

“…However, we found here that these same mutants are not sensitive to human serum in vitro, suggesting there is something present in vivo, beyond the antimicrobial activity of the complement cascade, that is responsible for the clearing of the NulO-deficient strains. This result is further supported by a recent study examining V. vulnificus YJ016 growth in serum that found the NulO biosynthetic genes were not involved in serum survival (59).…”

Genome sequence and pathogenicity ofVibrio vulnificusstrain MCCC 1A08743 isolated from contaminated prawns

“…By comparing the ANI value from strain MCCC 1A08743 and 211 other strains of V. vulnificus worldwide, we found that strain MCCC 1A08743 was most similar (99.99%) to strains derived from US clinical samples, which was consistent with the results of core genome comparison and phylogenetic analysis, and together, these results indicate that strain MCCC 1A08743 could harbour biological properties that are similar to those of strains from United States clinical samples. Although the V. vulnificus genes and processes leading to human diseases are not well understood, several canonical virulence factors of V. vulnificus either contributing to growth in serum, inflammation, immune evasion or invasion could be found in the genome of the strain MCCC 1A08743 ( Carda-Diéguez et al, 2018 ) such as hemolysin, VvpE ( Fan et al, 2001 ; Jones and Oliver, 2009 ), RtxA1 toxin ( Chung et al, 2010 ; Kim et al, 2008 ; Lee et al, 2007 ), the CPS, LPS ( Ellis and Kuehn, 2010 ; Vanaja et al, 2016 ), flagellum, and pili ( Jenne and Kubes, 2013 ; Lee et al, 2004 ). This was done by pathogenicity prediction analysis through VFDB databases.…”

Phylogeny and life cycle of the zoonotic pathogen Vibrio vulnificus

“…According to this model, vvhA (a gene mainly controlled by HlyU) would be upregulated under iron starvation by an unknown mechanism. Image modified from Hernández-Cabanyero et al (2019).is absolutely essential to survive and grow in human serum is the capsule (Carda-Diguez et al, 2018). The capsule of V. vulnificus confers resistance to both human complement and phagocytosis (Amaro et al, 1994;Williams et al, 2014;Carda-Diguez et al, 2018) and its biosynthesis is controlled by iron (Pajuelo et al, 2016).…”

“…Image modified from Hernández-Cabanyero et al (2019).is absolutely essential to survive and grow in human serum is the capsule (Carda-Diguez et al, 2018). The capsule of V. vulnificus confers resistance to both human complement and phagocytosis (Amaro et al, 1994;Williams et al, 2014;Carda-Diguez et al, 2018) and its biosynthesis is controlled by iron (Pajuelo et al, 2016). In fact, capsule biosynthesis is upregulated under ironexcess conditions in human serum (Hernández-Cabanyero et al, 2019), which would explain why the main risk factor predisposing humans to septicemia is iron.…”