Ntushelo Khayalethu
Department of Agriculture and Animal Health, Science Campus, University of South Africa, Corner Christian De Wet and Pioneer Avenue, Private Bag X6, 1710 Florida, South Africa.
Pak J Biol Sci. 2017;20(6):278-288. doi: 10.3923/pjbs.2017.278.288.
Salicylic acid is a signal molecule which activates plant defense against plant pathogens such as the soft rot enterobacterium Pectobacterium carotovorum subsp. carotovorum. The objectives of study were to determine bactericidal effects of salicylic acid on the growth of P. carotovorum subsp. carotovorum and secondly, assess chemical responses of P. carotovorum subsp. carotovorum to salicylic acid.
Pectobacterium carotovorum subsp. carotovorum was grown in lysogeny broth amended with salicylic acid at concentrations of 0, 100, 200, 400, 800 and 1200 mg L-1. The P. carotovorum subsp. carotovorum cultures were incubated at 25°C and sampled at two time points, 0 h (sampled before incubation) and 24 h. Bacterial counts were done at the onset of the incubation (0 h) and after the 24 h incubation. The set which was incubated for 24 h was split into two, one subset was centrifuged and the other was not. From the centrifuged subset the supernatant was recovered and was, together with all the other samples (0 and 24 h not centrifuged), analyzed with1H nuclear magnetic resonance and gas chromatography.
Bacterial counts done before and after incubation showed that the lower concentrations of salicylic acid, 0, 100, 200 and 400 mg L-1, supported the growth of P. carotovorum subsp. carotovorum whereas the higher concentrations of 800 and 1200 mg L-1 inhibited the growth of the bacterium completely. Nuclear magnetic resonance results showed either slight or no differences in the metabolite profiles and gas chromatography showed different responses without a clearly defined pattern among the experimental treatments. However, methanethiol was detected by both nuclear magnetic resonance and gas chromatography in all the treatments and was probably formed as a result of the breakdown of lysogeny broth.
From the results obtained it was concluded that salicylic acid promotes the growth of P. carotovorum subsp. carotovorum at lower concentrations of 0-400 mg L-1 but higher concentrations of salicylic acid of 800 and 1200 mg L-1 inhibit bacterial growth. All the tested salicylic acid concentrations (0-1200 mg L-1) cause only slight chemical shifts in the bacterial culture. Methanethiol was detected in all treatments and it is probably formed from the breakdown of lysogeny broth.
水杨酸是一种信号分子，可激活植物对植物病原体的防御，如软腐肠杆菌胡萝卜软腐果胶杆菌亚种。本研究的目的一是确定水杨酸对胡萝卜软腐果胶杆菌亚种生长的杀菌作用，二是评估胡萝卜软腐果胶杆菌亚种对水杨酸的化学反应。
将胡萝卜软腐果胶杆菌亚种接种于添加了浓度为0、100、200、400、800和1200 mg L-1水杨酸的溶菌肉汤中。胡萝卜软腐果胶杆菌亚种培养物在25°C下孵育，并在两个时间点取样，即0 h（孵育前取样）和24 h。在孵育开始时（0 h）和孵育24 h后进行细菌计数。将孵育24 h的菌液分成两份，一份离心，另一份不离心。从离心后的菌液中回收上清液，并与所有其他样品（0 h和24 h未离心的样品）一起用1H核磁共振和气相色谱进行分析。
孵育前后的细菌计数表明，较低浓度的水杨酸，即0、100、200和400 mg L-1，促进了胡萝卜软腐果胶杆菌亚种的生长，而较高浓度的800和1200 mg L-1则完全抑制了该细菌的生长。核磁共振结果显示代谢物谱略有差异或无差异，气相色谱显示不同处理之间有不同反应，但无明确模式。然而，在所有处理中，核磁共振和气相色谱均检测到甲硫醇，它可能是由溶菌肉汤分解形成的。
从获得的结果可以得出结论，水杨酸在0-400 mg L-1的较低浓度下促进胡萝卜软腐果胶杆菌亚种的生长，但800和1200 mg L-1的较高浓度水杨酸抑制细菌生长。所有测试的水杨酸浓度（0-1200 mg L-1）仅使细菌培养物产生轻微的化学位移。在所有处理中均检测到甲硫醇，它可能是由溶菌肉汤分解形成的。
