PRELIMINARY ANALYSIS OF THE FATTY ACID CONTENT IN ERWINIA AMYLOVORA AND ERWINIA ‘HORTICOLA’ STRAINS REVEALS THE DIFFERENCES BETWEEN THE CLOSELY-RELATED SPECIES
Minchuk Y1, Shapoval S1, Faidiuk Y1,2, Kharkhota M2, Moroz S 2, Tovkach F.2
1Taras Shevchenko National University of Kyiv, ESC Institute of Biology and Medicine
2D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine
A fact of Erwinia amylovora (Eam), a causative agent of the fire blight disease, being present on the territory of Ukraine is indisputable. A closely related pathogen causing similar symptoms in beech trees, Erwinia “horticola” (Eho), has also been isolated in far 60s of the 20th century, with its taxonomical position not established precisely yet. To reveal the distance between the species a comparative analysis of fatty acid (FA) content in Eam strains, isolated from tissues of affected quince, pear, as well as rowan-tree and pyracantha, against Eho collection strains has been performed.
Isolated Eam strains appeared to be a homogeneous group due to their FA content, which corresponded to that of collection strain Eam 9057. In contrast, Eho strains were shown to be a more heterogeneous group, with obvious differences vs Eam.
In both species the range of major acids includes 12:0, 14:0, 16:0; 16:1, 18:1 and 17:0cyc, while in Eho it also includes 17:0. Saturated even FA (SEFA) content is higher in Eam: 48.43±0.92% vs 39.30±1.36% in Eho. On the contrary, saturated odd FA (SOFA) content is higher in Eho strains: 5.25±1.7% vs 1.86±0.52% in Eam. While the content of unsaturated FA (UFA) is similar: 46.40±0.52% in Eam vs 45.37±0.03% in Eho. Thus, the ratio of SFA:UFA in both strains is close, being slightly higher in Eam 1.09±0.02% vs 0.99±0.05%. Similarly close is the content of hydroxy-FA (HFA), being slightly higher in Eam (0.21±0.04% vs 0.19±0.03%). The drastic difference in content can be seen in cyclic acids, being only 2.22±0.38% in Eam strains, while 9.19±2.40% in Eho, with the highest content of 13.33% in Eho 120 strain.
In addition to each set of strains, we have a species representatives suspected of being an R-variant that differed from the rest of the specific strains in their interaction with phages (collection strains Eam 8507 and Eho 60-3m). Their FA content reveals significant differences from the characteristic for the group. Namely, Eam 8507 deviates from other Eam strains in SEFA, as well in 12:0, 16:0, 18:1 and 17:0cyc content, being closer to Eho strains. While Eho 60-3m differs from species group in SEFA, SOFA, 16:0, 17:0, 16:1 and 17:0cyc content, being more similar to Eam in those values.
Thus, the FA analysis appeared to be a useful tool to differentiate E. “horticola” from E. amylovora. In combination with the phage typing, it provides the basis for revealing the differences among 2 closely-related species, despite their high identity in16S rRNA gene sequence being reported by other authors.