Biology subjects

Erickson, D. L.

Publications and source records attributed to Erickson, D. L..

5 recordsLinked to original sources

bioRxiv2025

Genetic control of Group 3 (K96) capsule synthesis and complement resistance in an extraintestinal pathogenic Escherichia coli ST69 strain

Extraintestinal pathogenic Escherichia coli (ExPEC) often produce capsules belonging to Groups 2 or 3, which contribute to invasive disease in humans and other animals. Group 3 capsule loci contain conserved kps genes flanking serotype-specific glycosyltransferase and nucleotide-sugar biosynthesis genes, but little is known about genetic factors that control synthesis, or the specific roles that K96 capsules play in virulence. Previously, we identified a Group 3 serotype K96 capsule in a mastitis-associated strain M12 that is critical for its survival in some host tissues. In this study, we show that the K96 capsule of strain M12 confers resistance to human serum complement. We conducted genetic screens to determine how K96 capsule expression is controlled, which led to two principal findings. First, Group 3 capsule synthesis is unstable. Sequencing of spontaneously appearing mutants revealed potential phase-variable control of capsule expression. Some mutants harbored reversible frameshift mutations in a homopolymeric site within kpsC, which were also identified in other K96-encoding ExPEC isolates. Second, a transposon mutagenesis screen revealed that capsule synthesis requires proteins encoded outside of the kps locus, including the RfaH antiterminator and OxyR transcriptional regulator, which control activation of an unusually distant promoter. An {Delta}oxyR mutant of strain M12 failed to produce capsule, was extremely sensitive to complement-mediated killing, and avirulent in Galleria mellonella. ImportanceGroup 2 capsules are established extraintestinal pathogenic Escherichia coli (ExPEC) virulence factors and are the type most often associated with human isolates. Group 3 capsules have previously been considered a sub-type of Group 2, although nothing was known about factors controlling their expression. Capsule serotype K96-encoding ExPEC strains are increasingly isolated from human infections and inhabit numerous other hosts. It is critical to understand the factors that enable their pathogenic versatility and survival in specific environments. Our study shows that K96 capsule of strain M12 is required for human complement resistance. Additionally, we have identified genetic factors that control Group 3 capsule synthesis, including a potential phase-variable mechanism as well as transcriptional control by OxyR. Co-regulation of Group 3 capsule synthesis genes with genes necessary for oxidative stress resistance may increase the virulence of some versatile ExPEC strains.

microbiology↗

bioRxiv2025

Opposing roles for iron transport systems in gallium tolerance in extraintestinal pathogenic Escherichia coli

Gallium is a promising antibacterial candidate because it displaces iron atoms inside bacterial cells but does not undergo redox cycling. It inhibits growth by disrupting essential iron-dependent processes. However, Escherichia coli are naturally less sensitive to gallium than many other bacteria, and the mechanisms that control gallium tolerance are not completely understood. We performed a genome-wide transposon sequencing (TnSeq) screen to identify genes important for the survival of an extraintestinal pathogenic E. coli isolate (M12) in gallium nitrate. The TnSeq results indicated that inactivation of enterobactin siderophore-related genes (entS, fepD, fes, fepB) enhances bacterial survival in gallium, while disrupting the ferric dicitrate transport system increases susceptibility. We validated these findings through targeted gene knockouts and gallium sensitivity experiments. Our findings suggest that enterobactin can complex with gallium for cellular uptake, but that the ferric citrate receptor FecA can discriminate between gallium citrate and iron citrate. Expression of fecA increased with gallium exposure, showing that gallium induces FecA-mediated iron uptake. Gallium also increased intracellular levels of manganese in the {Delta}fecA strain. Supplementation with iron or manganese restored growth of M12 {Delta}fecA in gallium, suggesting that gallium sensitivity is linked to both iron starvation and oxidative stress. As the ferric dicitrate transport system is an important virulence factor in several extraintestinal infection sites, our results suggest that targeting FecA may increase E. coli susceptibility to gallium while also suppressing virulence. ImportanceEscherichia coli extraintestinal infections that are resistant to traditional antibiotics are associated with more deaths than any other species. Gallium-based therapies may represent a non-antibiotic approach to treating extraintestinal pathogenic E. coli strains that affect both humans and animals. Our results are significant as they show that the enterobactin siderophore and the ferric dicitrate iron transport systems expressed by these bacteria have opposing roles in E. coli gallium sensitivity. These findings could be leveraged to enhance the efficacy of gallium therapeutics.

microbiology↗

bioRxiv2023

Genes associated with fitness and disease severity in the pan-genome of mastitis-associated Escherichia coli

Bovine mastitis caused by Escherichia coli may manifest as subclinical through severe acute disease and can be transient or persistent in nature. Little is known about bacterial factors that impact clinical outcomes or allow some strains to outcompete others in the mammary gland (MG) environment. Mastitis-associated E. coli (MAEC) may have distinctive characteristics which may contribute to the varied nature of the disease. In this study, we sequenced the genomes of 96 MAEC strains isolated from cattle with clinical mastitis (CM). We utilized clinical severity data to perform genome-wide association studies to identify accessory genes associated with strains isolated from mild or severe CM, or with high or low competitive fitness during in vivo competition assays. Genes associated with pathogenic or commensal strains isolated from bovine and avian sources were also identified. A type-2 secretion system (T2SS) and a chitinase (ChiA) exported by this system were strongly associated with pathogenic isolates compared with commensal strains. Strains carrying these genes also had higher competitive fitness during experimental intramammary infections. Deletion of chiA from MAEC isolates decreased their adherence to cultured bovine mammary epithelial cells, suggesting that the increased fitness associated with strains possessing this gene may be due to better attachment in the MG. ImportanceBovine mastitis caused by MAEC compromises animal health and inflicts substantial product losses in dairy farming. Given their high levels of intraspecies genetic variability, virulence factors of commonly used MAEC model strains may not be relevant to all members of this group. Here we analyzed clinical data as well as fitness (quantified in a mouse MG model) of diverse MAEC isolates to identify accessory genes that contribute to infection. We demonstrated a novel role for chitinase in promoting attachment to mammary epithelial cells. Reverse genetic approaches can be applied to the collection of strains and their complete genome sequences that we have presented here. Overall, these results provide a much richer understanding of MAEC and suggest bacterial processes that may underlie the clinical diversity associated with mastitis and their adaptation to this unique environment.

microbiology↗

bioRxiv2020

A link between zinc uptake, bile salts, and a capsule required for virulence of a mastitis-associated extraintestinal pathogenic Escherichia coli strain

Extraintestinal pathogenic Escherichia coli (ExPEC) are major causes of urinary and bloodstream infections. ExPEC reservoirs are not completely understood. Some mastitis-associated E. coli (MAEC) strains carry genes associated with ExPEC virulence, including metal scavenging, immune avoidance, and host attachment functions. In this study, we investigated the role of the high-affinity zinc uptake (znuABC) system in the MAEC strain M12. Elimination of znuABC moderately decreased fitness during mouse mammary gland infections. The {Delta}znuABC mutant strain exhibited an unexpected growth delay in the presence of bile salts, which was alleviated by the addition of excess zinc. We isolated {Delta}znuABC mutant suppressor mutants with improved growth of in bile salts, several of which no longer produced the K96 capsule made by strain M12. Addition of bile salts also reduced capsule production by strain M12 and ExPEC strain CP9, suggesting that capsule synthesis may be detrimental when bile salts are present. To better understand the role of the capsule, we compared the virulence of mastitis strain M12 with its unencapsulated {Delta}kpsCS mutant in two models of ExPEC disease. The wild type strain successfully colonized mouse bladders and kidneys and was highly virulent in intraperitoneal infections. Conversely, the {Delta}kpsCS mutant was unable to colonize kidneys and was unable to cause sepsis. These results demonstrate that some MAEC may be capable of causing human ExPEC illness. Virulence of strain M12 in these infections is dependent on its capsule. However, capsule may interfere with zinc homeostasis in the presence of bile salts while in the digestive tract.

microbiology↗

bioRxiv2020

A trimeric autotransporter enhances biofilm cohesiveness in Yersinia pseudotuberculosis but not in Yersinia pestis

Cohesion of biofilms made by Yersinia pestis and Yersinia pseudotuberculosis (Yptb) has been attributed solely to an extracellular polysaccharide matrix encoded by the hms genes (Hms-ECM). However, mutations in the Yptb BarA/UvrY/CsrB regulatory cascade enhance biofilm stability without dramatically increasing Hms-ECM production. We found that treatment with proteinase K enzyme effectively destabilized Yptb csrB mutant biofilms, suggesting that cell-cell interactions might be mediated by protein adhesins or extracellular matrix proteins. We identified an uncharacterized trimeric autotransporter lipoprotein (YPTB2394), repressed by csrB, which has been referred to as YadE. Biofilms made by a {Delta}yadE mutant strain were extremely sensitive to mechanical disruption. Overexpression of yadE in wild-type Yptb increased biofilm cohesion, similar to biofilms made by csrB or uvrY mutants. We found that the Rcs signaling cascade, which represses Hms-ECM production, activated expression of yadE. The yadE gene appears to be functional in Yptb but is a pseudogene in modern Y. pestis strains. Expression of functional yadE in Y. pestis KIM6+ altered the production of Hms-ECM and weakened biofilms made by these bacteria. This suggests that although the YadE autotransporter protein increases Yptb biofilm stability, it may be incompatible with Hms-ECM production that is essential for Y. pestis biofilm production in fleas. Inactivation of yadE in Y. pestis may be another instance of selective gene loss in the evolution of flea-borne transmission by this species. IMPORTANCEThe evolution of Yersinia pestis from its Y. pseudotuberculosis (Yptb) ancestor involved gene acquisition and gene losses, leading to differences in biofilm production. Characterizing the unique biofilm features of both species may provide better understanding of how each adapts to its specific niches. This study identifies a trimeric autotransporter YadE that promotes biofilm stability of Yptb but which has been inactivated in Y. pestis, likely because it is not compatible with Hms polysaccharide that is crucial for biofilms inside fleas. We also reveal that the Rcs signaling cascade, which represses Hms expression in Y. pestis, activates YadE in Yptb. The ability of Yptb to use polysaccharide or YadE protein for cell-cell adhesion may help it produce biofilms in different environments.

microbiology↗