Abstract
Presumptive phage particles associated with Xylella fastidiosa strain Temecula-1 grown in PW broth were observed by transmission electron microscopy (TEM) in ultrathin sections of bacterial cell-containing low speed centrifugation pellets and in partially purified preparations from CsCl equilibrium centrifugation density gradients. Ultrathin-sectioned cell pellets contained icosahedral particles of about 45 nm in diameter. Samples collected from CsCl density gradients revealed mostly non-tailed icosahedral but also tailed particles. The icosahedral particles could be divided into two types: a large type (about 45 nm) and a small type (about 30 nm). Filamentous phage-like particles (17 × 120 to 6,300 nm) were also observed. The presence of different types of phage-like particles resembling to those in several bacteriophage families provides new physical evidence, in addition to X. fastidiosa genomic information, that X. fastidiosa possesses active phages. This is the first report of phage particles released in X. fastidiosa cultures.
Highlights
The sequence shared high similarity to that of an integrase gene in the Podoviridae phage family. This sequence is absent in the whole genome sequence of a California Pierce's disease (PD) strain Temecula-1, but is present in other California PD strains
We report our observations of presumptive phage particles in a X. fastidiosa PD strain through transmission electron microscopy (TEM)
The presence of different types of phage-like particles resembling those in several bacteriophage families provides new physical evidence, in addition to X. fastidiosa genomic information, that X. fastidiosa possesses active phages
Summary
Xylella fastidiosa [1] is a Gram negative plant pathogen causing many economically important diseases including Pierce's disease (PD) of grapevine, almond leaf scorch disease and citrus variegated chlorosis disease. We report our observations of presumptive phage particles in a X. fastidiosa PD strain through transmission electron microscopy (TEM). TEM images of X. fastidosa bacteria published earlier [13] include morphologically similar phage-like particles; there was no discussion or interpretation of these. After layering the resuspended high speed centrifugation pellets (0.2–1.0 ml) on the tops, the gradients were centrifuged at 155,000 g for 18–21 hours and a presumptive phage particle-containing band was observed (data not shown). Samples collected from CsCl density gradients revealed the presence of mostly non-tailed icosahedral particles, which could be grouped into two types. The large type particles were about 45 nm (Fig. 1B), similar to those observed from cell pellets (Fig. 1A). Optimization of the phage isolation and purification procedure is needed for future research
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