A SNP in the Cache 1 Signaling Domain of Diguanylate Cyclase STM1987 Leads to Increased In Vivo Fitness of Invasive Salmonella Strains

Abstract

Nontyphoidal Salmonella (NTS) strains are associated with gastroenteritis worldwide but are also the leading cause of bacterial bloodstream infections in sub-Saharan Africa. The invasive NTS (iNTS) strains that cause bloodstream infections differ from standard gastroenteritis-causing strains by >700 single-nucleotide polymorphisms (SNPs). These SNPs are known to alter metabolic pathways and biofilm formation and to contribute to serum resistance and are thought to signify iNTS strains becoming human adapted, similar to typhoid fever-causing Salmonella strains. Identifying SNPs that contribute to invasion or increased virulence has been more elusive. In this study, we identified a SNP in the cache 1 signaling domain of diguanylate cyclase STM1987 in the invasive Salmonella enterica serovar Typhimurium type strain D23580. This SNP was conserved in 118 other iNTS strains analyzed and was comparatively absent in global S. Typhimurium isolates associated with gastroenteritis. STM1987 catalyzes the formation of bis-(3′,5′)-cyclic dimeric GMP (c-di-GMP) and is proposed to stimulate production of cellulose independent of the master biofilm regulator CsgD. We show that the amino acid change in STM1987 leads to a 10-fold drop in cellulose production and increased fitness in a mouse model of acute infection. Reduced cellulose production due to the SNP led to enhanced survival in both murine and human macrophage cell lines. In contrast, loss of CsgD-dependent cellulose production did not lead to any measurable change in in vivo fitness. We hypothesize that the SNP in stm1987 represents a pathoadaptive mutation for iNTS strains.

In vitro and ex vivo modeling of enteric bacterial infections

“…One example is a missense mutation found in the cache 1 signaling domain of the di-guanylate cyclase STM1987 of the invasive Salmonella enterica serovar Typhimurium ST131 clone that recently emerged in sub-Saharan Africa. 56 This variant was shown to drastically reduce cellulose production and displayed increased fitness both in vitro and in vivo virulence models.…”

Yin and Yang of Biofilm Formation and Cyclic di-GMP Signaling of the Gastrointestinal Pathogen <b><i>Salmonella enterica</i></b> Serovar Typhimurium

“…A particularly invasive S. Ty- phimurium clone, ST313, with enhanced virulence resembling typhoid fever and reduced biofilm formation, has emerged in Africa in HIV and malaria infected individuals and upon malnutrition [94]. The infection process of S. Typhimurium is regulated by cyclic di-GMP signaling and biofilm components at various stages as dissected by experimental studies with cell culture and animal models to show unique and distinct contributions of individual cyclic di-GMP turnover proteins (see below; [69,83,91,[95][96][97]).…”

“…The infection process of S . Typhimurium is regulated by cyclic di-GMP signaling and biofilm components at various stages as dissected by experimental studies with cell culture and animal models to show unique and distinct contributions of individual cyclic di-GMP turnover proteins (see below; [ 69 , 83 , 91 , 95 , 96 , 97 ]).…”

“…Of note, ST313 clone members of S. Typhimurium possess a number of single nucleotide polymorphisms inside open reading frames and in intergenic regions, which have been shown to modulate virulence of this organism. For example, an amino acid substitution in the sensory Cache 1 domain of the diguanylate cyclase STM1987 causes reduced cellulose production but enhanced murine and human macrophage survival [ 97 ]. Equally, ST313 representatives harbor mutations in the gene for the alkaline phosphatase superfamily member BcsG [ 115 ].…”

Genome-wide fitness analysis identifies genes required for in vitro growth and macrophage infection by African and global epidemic pathovariants of Salmonella enterica Enteritidis

“…Research on bloodstream-infection-associated African Salmonella has been focused on the S . enterica Typhimurium serovar [25–42]. The Feasey et al .…”