The filamentous phage XacF1 causes loss of virulence in Xanthomonas axonopodis pv. citri, the causative agent of citrus canker disease

Abstract

In this study, filamentous phage XacF1, which can infect Xanthomonas axonopodis pv. citri (Xac) strains, was isolated and characterized. Electron microscopy showed that XacF1 is a member of the family Inoviridae and is about 600 nm long. The genome of XacF1 is 7325 nucleotides in size, containing 13 predicted open reading frames (ORFs), some of which showed significant homology to Ff-like phage proteins such as ORF1 (pII), ORF2 (pV), ORF6 (pIII), and ORF8 (pVI). XacF1 showed a relatively wide host range, infecting seven out of 11 strains tested in this study. Frequently, XacF1 was found to be integrated into the genome of Xac strains. This integration occurred at the host dif site (attB) and was mediated by the host XerC/D recombination system. The attP sequence was identical to that of Xanthomonas phage Cf1c. Interestingly, infection by XacF1 phage caused several physiological changes to the bacterial host cells, including lower levels of extracellular polysaccharide production, reduced motility, slower growth rate, and a dramatic reduction in virulence. In particular, the reduction in virulence suggested possible utilization of XacF1 as a biological control agent against citrus canker disease.

First Report on Characterization of Citrus Disease Causing Bacteria and Related Phages Isolated in Pakistan

“…Similar results obtained for X. axonopodis pv. citri phages that were isolated in Japan (Ahmad et al, 2014).…”

“…The results were promising as phage application significantly reduced disease severity. Most recently a well characterized filamentous phage showed wide host range, reduced the ability of the bacterial cells to produce extracellular polysaccharides (EPS), reduced the motility, slowed the growth rate and significantly reduced the virulence (Ahmad et al, 2014).…”

Application of filamentous phages in environment: A tectonic shift in the science and practice of ecorestoration

“…In these bacterial hosts, filamentous phages either carry the virulence gene(s) (Addy et al, ; Derbise & Carniel, ; Waldor & Mekalanos, ) or regulate the expression of virulence factors (Addy, Askora, Kawasaki, Fujie, & Yamada, , b; Ahmad et al, ). For example, N. meningitidis and Y. pestis are transformed into virulent strains capable of causing epidemics after receiving the toxin gene from Nf or MDA and from YpfΦ phage, respectively (Bille et al, ; Derbise et al, ).…”

“…IAA producer Datta and Basu (2000), Bhattacharyya and Pati (2000) sp Fukushima, Shimizu, and Inatsu (2011) Fetherston, Lillard, and Perry (1995) beneficial if the bacterial host happens to be a plant pathogen (Ahmad, Askora, Kawasaki, Fujie, & Yamada, 2014;Yamada, 2013).…”

“…Mostly, a phage infection enhances the host's ability to combat abiotic and biotic stress, to invade a new habitat, and to partake in the development of microbial communities (Askora & Yamada, ; Bille et al, ; Derbise & Carniel, ; Jian, Xiao, & Wang, ; Mai‐Prochnow et al, ; Rice et al, ; Shapiro et al, ; Waldor & Mekalanos, ; Webb, Lau, & Kjelleberg, ; Yu et al, ). However, at times a phage infection lowers the fitness of the host bacterium, which is also beneficial if the bacterial host happens to be a plant pathogen (Ahmad, Askora, Kawasaki, Fujie, & Yamada, ; Yamada, ). Filamentous phages are useful for manipulating bacteria for environmental applications because the phages are stably produced in their bacterial hosts and are easy to manipulate using genetic and chemical methods—however, they remain underexploited in current practice.…”