Natural Competence Rates Are Variable Among Xylella fastidiosa Strains and Homologous Recombination Occurs In Vitro Between Subspecies fastidiosa and multiplex

Abstract

TitleNatural competence rates are variable among xylella fastidiosa strains and homologous recombination occurs in vitro between subspecies fastidiosa and multiplex Xylella fastidiosa, an etiological agent of emerging crop diseases around the world, is naturally competent for the uptake of DNA from the environment that is incorporated into its genome by homologous recombination. Homologous recombination between subspecies of X. fastidiosa was inferred by in silico studies and was hypothesized to cause disease emergence. However, no experimental data are available on the degree to which X. fastidiosa strains are capable of competence and whether recombination can be experimentally demonstrated between subspecies. Here, using X. fastidiosa strains from different subspecies, natural competence in 11 of 13 strains was confirmed with plasmids containing antibiotic markers flanked by homologous regions and, in three of five strains, with dead bacterial cells used as source of donor DNA. Recombination frequency differed among strains and was correlated to growth rate and twitching motility. Moreover, intersubspecific recombination occurred readily between strains of subsp. fastidiosa and multiplex, as demonstrated by movement of antibiotic resistance and green fluorescent protein from donor to recipient cells and confirmed by DNA sequencing of the flanking arms of recombinant strains. Results demonstrate that natural competence is widespread among X. fastidiosa strains and could have an impact in pathogen adaptation and disease development.

Xylella fastidiosa: Insights into an Emerging Plant Pathogen

“…Genetically typing X. fastidiosa was challenging because this bacterium is naturally competent (79) and populations undergo extensive homologous recombination (HR) within and among phylogenetic clades (3,28,75,(98)(99)(100)(101)103). In 2005, a multilocus sequence typing (MLST) scheme for X. fastidiosa was first introduced (130), leading to substantial improvement in understanding the phylogenetic relationships among isolates and how clades are organized in relation to both host plants and geographical location.…”

“…How common coinfections are in nature and how conducive these environments are for recombination remain to be determined, but the sympatric coexistence of multiple genotypes likely facilitates such processes. Although competency may be a conserved trait in X. fastidiosa, there are differences in transformation efficiency among subspecies and closely related strains (75).…”

Calcium transcriptionally regulates movement, recombination and other functions of Xylella fastidiosa under constant flow inside microfluidic chambers

“…Interestingly, in Flask‐RNA‐Seq, genes recJ , recD and comA involved in recombination and competence were also upregulated in 4Ca (Table ) (Parker et al , ). Moreover, twitching motility of X. fastidiosa , which has been reported to be important for natural transformation (Kandel et al , ), was enhanced in 2Ca. Taking these results into consideration, we hypothesized that 2 mM external Ca contributes to natural competence of X. fastidiosa .…”

Conjugative Plasmid Transfer in Xylella fastidiosa Is Dependent on tra and trb Operon Functions

“…Conjugative plasmid transfer, which can mediate transfer of DNA segments as large as the plasmids themselves, is not reliant on immediate integration for stability of the transferred DNA and therefore has the potential to move more genetic material in one transfer event than natural transformation. Recombination events of up to ϳ3.5 kb in length that are associated with natural transformation in X. fastidiosa have been identified (5). Classic examples of conjugative plasmid transfer, such as the E. coli F-like plasmids, involve transfer of up…”

“…X. fastidiosa is broadly categorized into multiple subspecies, which often have distinct host ranges. The emergence of new diseases caused by X. fastidiosa is thought to be, in part, a result of frequent horizontal gene transfer (HGT) and recombination events between related strains and in some cases between subspecies (3)(4)(5). A significant amount of this HGT is likely due to natural transformation and has been extensively characterized under a variety of in vitro conditions (6)(7)(8)(9).…”