Antibacterial Potential of Salicylic Acid against PCC

Plants exhibit defense mechanism against pathogen attack by producing certain chemical compounds. Salicylic Acid (SA) is one of them which provide shield against pathogens^1,2. According to many investigations these phenolic compounds play chief role as signal molecule for activation of Pathogen Associated Molecular Pattern (PAMP)-triggered immunity (PTI), Effector-Triggered Immunity (ETI) and Systemic Acquired Resistance (SAR) following infection by pathogens^3,4. Czajkowski and team⁵ reported that SA restrains infection produced by Dickeya solani of potato. Moreover; Lagonenko and colleagues⁶ conducted a research and noted that SA attenuates biofilm formation, motility and N-Acyl homoserine lactone produced by Pectobacterium carotovorum and Pseudomonas syringae pv. syringae at sub inhibitory concentrations.

However, defensive mechanism of SA against many pathogenic bacteria is still not known. Khayalethu Ntushelo conducted an experiment to investigate the antibacterial influence of salicylic acid against P. carotovorum subsp. carotovorum (Pcc) and to evaluate the chemical responses of Pcc to salicylic acid. In this experiment, scientists grew the Pectobacterium carotovorum subsp. carotovorum in lysogeny broth containing salicylic acid at concentrations of 0, 100, 200, 400, 800 and 1200 mg L^–1. The Pcc cultures were incubated at 25°C and sampled at two time points, 0 hours (sampled before incubation) and 24 hours. Bacterial cells were counted at the beginning of the incubation (0 h) and after the 24 h incubation. The Pcc culture set which was incubated for 24 h was divided into two clusters among which only one subset was centrifuged. From the centrifuged subset the supernatant was recovered and mutually with all the other samples (0h and 24 h not centrifuged), analyzed with¹H nuclear magnetic resonance and gas chromatography.

Scientists noted that salicylic acid triggers the growth of Pectobacterium carotovorum subsp. carotovorum at minor concentrations but SA attenuates growth of this bacteriumat elevated concentrations. Moreover, only insignificant shifts in both nuclear magnetic resonance and gas chromatography profiles take place when this bacterium is exposed to concentrations up to 1200 mg L^–1. Perhaps Methanethiol (common compound in lysogeny broth cultures of Pcc) is also produced after catalysis of lysogeny broth. Accordingly; scientists stated that plants having elevated levels of SA may restrain the growth of pathogen such as P. carotovorum subsp. carotovorum.

References:

1. Chen, Z., H. Silva and D.F. Klessig, 1993. Active oxygen species in the induction of plant systemic acquired resistance by salicylic acid. Science, 262: 1883-1886.
2. Mills, P.R. and R.K.S. Wood, 1984. The effects of polyacrylic acid, acetylsalicylic acid and salicylic acid on resistance of cucumber to Colletotrichum lagenarium. J. Phytopathol., 111: 209-216.
3. An, C. and Z. Mou, 2011. Salicylic acid and its function in plant immunity. J. Integr. Plant Biol., 53: 412-428.
4. Vlot, A.C., D.A. Dempsey and D.F. Klessig, 2009. Salicylic acid, a multifaceted hormone to combat disease. Annu. Rev. Phytopathol., 47: 177-206.
5. Czajkowski, R., J.M. van der Wolf, A. Krolicka, Z. Ozymko, M. Narajczyk, N. Kaczynska and E. Lojkowska, 2015. Salicylic acid can reduce infection symptoms caused by Dickeya solani in tissue culture grown potato (Solanum tuberosum) plants. Eur. J. Plant Pathol., 141: 545-558.
6. Lagonenko, L., A. Lagonenko and A. Evtushenkov, 2013. Impact of salicylic acid on biofilm formation by plant pathogenic bacteria. J. Biol. Earth Sci., 3: B176-B181.