Bulyhina T.

D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine,

Department of microorganisms biochemistry

е-mail: tati20@ukr.net

Introduction. Viral plant diseases are widespread in agro- and biocenoses; in their harmfulness they often come out on top, outstripping other pathogens. These viruses include the tobacco mosaic virus (TMV), which mainly infects crops such as cucumbers, tomatoes, potatoes, tobacco, and peppers. Considering the absolute parasitism of viruses in plants and the lack of an integral immune metabolic system, the prevention and control of viral plant diseases is currently a serious problem. In recent years, it has been shown that lipopolysaccharides (LPSs) of some bacteria, in particular representatives of the genus Pseudomonas, play an essential role in the interaction of plants with pathogens. They activate and trigger the expression of plant defense mechanisms in response to infection caused by fungi or bacteria. But the development of promising biological products for practice, which would inhibit the development of plant viruses, is still at an early stage. Therefore, the aim of the present work was to study the effects of Pantoea agglomerans LPSs and their structural components on the infectivity of TMV in vitro.

Methods. P. agglomerans LPSs were isolated from dry bacterial mass by phenol-water method. LPS mild acid degradation allowed to separate OPS from lipid A, which structures were identified by sugar analysis, 2D NMR spectroscopy, and by ESI-MS spectrometry, respectively. The antiviral activity of LPS preparations was investigated in vitro on a model of tobacco mosaic virus (TMV), strain U1, purified from systemically infected plants of Nicotiana tabacum L. cv. “varieties” Immunny 580. LPS preparations (1 mg/mL) were added to the inoculum (TMV, 1 μg/mL) in the ratio (1:1) 30 min before plant inoculation.

Results and discussions. Most of the studied LPS preparations at a concentration of 1 mg/mL reduced the infectivity of TMV by 18-60%. The most active were LPSs from P. agglomerans P324 and 8488, the antiviral activity of which was 59-60%. LPS preparations of P. agglomerans 7969, 7604, and 9637 were found to be inactive against TMV in vitro. Comparative analysis of the antiviral activity of the LPS structural components of two P agglomerans strains P324 and 7604 showed that the greatest inhibitory effect on the TMV infectivity was exhibited by lipid A from P. agglomerans P324, the antiviral activity of which practically did not differ from the activity of the LPS molecule (it was lower by 7%). At the same time, the inhibitory effect of the carbohydrate structural components of P. agglomerans 7604 (especially the II and III fractions of core OG) compared with the effect of the whole LPS molecule against TMV was slightly higher. Modification of the initial LPS 7460 by succinylation did not change an antiviral activity. According to electron microscopy data, the virions stuck together forming the sheafs at the direct LPS-virus contact in vitro whereas the single free virus particles were observed in the control.

Conclusions. The results of studies on the effect of P. agglomerans LPS indicate that the activity of the initial LPS molecule is determined by the structural features of lipid A. A more detailed study of the effect of individual structural components will help in understanding the regularities of the effect of the LPS structure on TMV infectivity. Evidence of direct interaction between P. agglomerans strain LPSs and TMV virus is provided.