Protection of Erwinia amylovora bacteriophage Y2 from UV-induced damage by natural compounds

Abstract

Bacteriophages have regained much attention as biocontrol agents against bacterial pathogens. However, with respect to stability, phages are biomolecules and are therefore sensitive to a number of environmental influences. UV-irradiation can readily inactivate phage infectivity, which impedes their potential application in the plant phyllosphere. Therefore, phages for control of Erwinia amylovora, the causative agent of fire blight, need to be protected from UV-damage by adequate measures. We investigated the protective effect of different light-absorbing substances on phage particles exposed to UV-light. For this, natural extracts from carrot, red pepper, and beetroot, casein and soy peptone in solution, and purified substances such as astaxanthin, aromatic amino acids, and Tween 80 were prepared and tested as natural sunscreens for phage. All compounds were found to significantly increase half-life of UV-irradiated phage particles and they did not negatively affect phage viability or infectivity. Altogether, a range of readily available, natural substances are suitable as UV-protectants to prevent phage particles from UV-light damage.

Keywords: Erwinia amylovora; UV damage; betalaines; carotenoids; fire blight; phage; stability.

Figure 1.

Effect of carrot, red pepper, and beetroot juice on the time-dependent decay of UV-irradiated phage particles. Values indicate means of 3 independent experiments ± standard deviations. (A): Carrot juice, circles: control without protectant, squares: 1% carrot juice, triangles: 10% carrot juice. (B): Red pepper juice, circles: control without protectant, triangles: 5% red pepper juice. (C): Beetroot juice, circles: control without protectant, squares: 1% beetroot juice, triangles: 10% beetroot juice.

Figure 2.

Effect of pure aromatic amino acids (Tyr, Trp, Phe) and peptides (peptone and casein) on the time-dependent decay of UV-irradiated phage particles. Values indicate means of 3 independent experiments ± standard deviations. (A): amino acids, circles: control without protectant, squares: 5 mM amino acids, triangles: 50 mM amino acids. (B): Peptone, circles: control without protectant, triangles: 50 mg/ml peptone. (C): Casein, circles: control without protectant, squares: 5 mg/ml casein, triangles: 10 mg/ml casein.

Figure 3.

Effect of astaxanthin and Tween 80 on the time-dependent decay of UV-irradiated phage particles. Values indicate means of 3 independent experiments ± standard deviations. (A): Astaxanthin, circles: control without protectant, triangles: 3 mg/ml astaxanthin. (B): Tween 80, circles: control without protectant, triangles: 5 % Tween 80.