HecA, a member of a class of adhesins produced by diverse pathogenic bacteria, contributes to the attachment, aggregation, epidermal cell killing, and virulence phenotypes of Erwinia chrysanthemi EC16 on Nicotiana clevelandii seedlings

Abstract

Erwinia chrysanthemi is representative of a broad class of bacterial pathogens that are capable of inducing necrosis in plants. The E. chrysanthemi EC16 hecA gene predicts a 3,850-aa member of the Bordetella pertussis filamentous hemagglutinin family of adhesins. A hecA::Tn7 mutant was reduced in virulence on Nicotiana clevelandii seedlings after inoculation without wounding. Epifluorescence and confocal laser-scanning microscopy observations of hecA and wildtype cells expressing the green fluorescent protein revealed that the mutant is reduced in its ability to attach and then form aggregates on leaves and to cause an aggregate-associated killing of epidermal cells. Cell killing also depended on production of the major pectate lyase isozymes and the type II, but not the type III, secretion pathway in E. chrysanthemi. HecA homologs were found in bacterial pathogens of plants and animals and appear to be unique to pathogens and universal in necrogenic plant pathogens. Phylogenetic comparison of the conserved two-partner secretion domains in the proteins and the 16S rRNA sequences in respective bacteria revealed the two datasets to be fundamentally incongruent, suggesting horizontal acquisition of these genes. Furthermore, hecA and its two homologs in Yersinia pestis had a G؉C content that was 10% higher than that of their genomes and similar to that of plant pathogenic Ralstonia, Xylella, and Pseudomonas spp. Our data suggest that filamentous hemagglutinin-like adhesins are broadly important virulence factors in both plant and animal pathogens. B acterial attachment to host tissues by various adhesins is a first step in the pathogenesis of many animal pathogens, but a role for attachment in plant pathogenesis is less clear. The exception is the tumorigenic pathogen Agrobacterium tumefaciens, whose attachment to plant tissues before transfer of T-DNA (the portion of the tumor-inducing Ti plasmid that is transferred to plant cells) involves a Ca 2ϩ -dependent adhesin (1), a repertoire of proteins encoded by att (attachment) genes (2-4), exo-and capsular polysaccharides (5, 6), and bacterial cellulose fibrils (5). In contrast, the role of attachment and adhesins in virulence is unclear for the more prevalent necrogenic (rather than tumorigenic) plant pathogens. These bacteria colonize the surface and intercellular spaces of plants and attack with various combinations of virulence effector proteins injected by type III secretion systems, extracellular pectic enzymes, and low molecular-weight toxins.The necrogenic pathogens have been reported to produce a variety of potential adhesins, including fimbriae by Erwinia rhapontici, Erwinia carotovora, Pseudomonas syringae (7), Xanthomonas campestris (8), and Ralstonia solanacearum (9), type IV pili by P. syringae (10), and adhesive factors such as lipopolysaccharide by R. solanacearum (11). Attachment to leaf surfaces by type IV pili slightly promotes the epiphytic fitness of P. syringae (12), and the related process of self aggregation is also promoted in P. syringae by t...

The louse-borne human pathogen Bartonella quintana is a genomic derivative of the zoonotic agent Bartonella henselae

“…2a) are multiple copies of fhaC͞hecB and fhaB that form a two-partner secretion system (27), where the fhaC͞ hecB gene product mediates transport of filamentous hemagglutinin encoded by fhaB. A phylogenetic analysis of two-partner domains suggests that these may be horizontally transmitted across species (28), which is consistent with their location on genomic islands in B. henselae. The fhaB homologs are flanked by sequences putatively coding for proteins of 138 aa that are repeated 20 times in the B. henselae genome.…”

Type I and type IV pili of Xylella fastidiosa affect twitching motility, biofilm formation and cell–cell aggregation

“…When the gene hxfA (PD2118) was disrupted, the ability to form aggregates in liquid culture was impaired. The haemagglutinin adhesions produced by Erwinia chrysanthemi have also been shown to contribute to aggregation (Rojas et al, 2002). When either or both type I and type IV pili are present, larger aggregates are formed, suggesting a role for pili (Figs 4 and 5).…”

The complete genome sequence of the Arabidopsis and tomato pathogen Pseudomonas syringae pv. tomato DC3000

“…Analysis of the 23 Tfp-associated genes suggests that regulation of Tfp production differs significantly between DC3000 and P. aeruginosa. Filamentous hemagglutinin (FHA) has also been shown to be an adhesin and a virulence factor in animal pathogenic bacteria and the plant pathogen Erwinia chrysanthemi (51). Three genes predicting FHA-like proteins were identified in DC3000 (PSPTO3210, 3214, and 3229).…”