Acinetobacter calcoaceticus CSY-P13 Mitigates Stress of Ferulic and p-Hydroxybenzoic Acids in Cucumber by Affecting Antioxidant Enzyme Activity and Soil Bacterial Community

Abstract

Ferulic acid (FA) and p-hydroxybenzoic acid (PHBA) are main phenolic compounds accumulated in rhizosphere of continuously cropped cucumber, causing stress in plants. Microbial degradation of a mixture of FA and PHBA is not well understood in soil. We isolated a strain CSY-P13 of Acinetobacter calcoaceticus, inoculated it into soil to protect cucumber from FA and PHBA stress, and explored a mechanism underlying the protection. CSY-P13 effectively degraded a mixture of FA and PHBA in culture solution under conditions of 39.37°C, pH 6.97, and 21.59 g L-1 potassium dihydrogen phosphate, giving rise to 4-vinyl guaiacol, vanillin, vanillic acid, and protocatechuic acid. During FA and PHBA degradation, activities of superoxide dismutase (SOD), catalase, ascorbate peroxidase, and dehydroascorbate reductase in CSY-P13 were induced. Inoculated into cucumber-planted soil containing 220 μg g-1 mixture of FA and PHBA, CSY-P13 degraded FA and PHBA in soil, increased plant height, and decreased malonaldehyde, superoxide radical, and hydrogen peroxide levels in leaves. CSY-P13 also enhanced SOD, guaiacol peroxidase, catalase, glutathione peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase activities; increased ascorbate and glutathione contents; and elevated transcript levels of copper/zinc SOD, manganese SOD, and catalase in leaves under FA and PHBA. Moreover, CSY-P13 increased phosphatase, catalase, urease, and sucrase activities and changed bacterial richness, diversity, and community composition by high throughput sequencing in cucumber-planted soil supplemented with the mixture of FA and PHBA. So CSY-P13 degrades the mixture of FA and PHBA in soil and mitigates stress from the two phenolic compounds in cucumber by activating antioxidant enzymes, changing soil bacterial community, and inducing soil enzymes.

Transcriptome Profiling Combined With Activities of Antioxidant and Soil Enzymes Reveals an Ability of Pseudomonas sp. CFA to Mitigate p-Hydroxybenzoic and Ferulic Acid Stresses in Cucumber

“…To incubate CFA, 2 ml of strain cultures grown exponentially in Luria-Bertani (LB) liquid medium were inoculated into 100 ml of liquid M-9 medium supplemented with a mixture of PHBA and FA in the ratio of 42.82: 57.18 (Wu et al, 2018). Cell growth of CFA was measured at 600 nm (Mathew et al, 2007).…”

“…To promptly analyze the properties of CFA, the strain was incubated at 180 rpm for 6 h, and the percentages of degraded PHBA and FA in M-9 medium were preliminarily assessed at 247 and 320 nm, respectively. Based on the properties of CFA, Box-Behnken design was used to optimize the PHBA and FA degradation by CFA (Wu et al, 2018). The levels and codes of independent variables are given in Supplementary Table 1.…”

“…Then, cells of the strain were collected into autoclaved water. Each cucumber seedling was cultivated in one pot containing 450 g of autoclaved soil (Wu et al, 2018). At the two-leaf stage, 32 cucumber seedlings were divided into four groups (8 plants per group).…”

“…The strain CFA was inoculated into M-9 medium supplemented with the optimized concentration (0.2 g/l) of the mixture of PHBA and FA and incubated at 180 rpm and the optimized temperature (37 • C). As controls, the strain was inoculated into M-9 medium supplemented with 85.6 mg/l PHBA, 114.4 mg/l FA, or 306.88 mg/l glucose (Wu et al, 2018). The activities of SOD (Hwang et al, 1999), CAT (Pereira et al, 2002), and DHAR (Hoque et al, 2007) were determined in CFA.…”

Bioremediation of Historically Chlorimuron-Ethyl-Contaminated Soil by Co-Culture Chlorimuron-Ethyl-Degrading Bacteria Combined with the Spent Mushroom Substrate

“…Changes in SP (soluble protein) content can reflect protein synthesis, denaturation and degradation in cells, and the SP content of plants is reduced under the stresses of chilling, heavy metals, various organic chemicals, and air pollutants. Therefore, changes in SP content and SOD activity may be considered biomarkers of serious stress caused by chlorimuron-ethyl in the soil [4,42]. Figure 6 (A) shows that the SOD activity of each experimental group increased with growing time, indicating that chlorimuron-ethyl accumulates in wheat and that increased SOD activity will help to alleviate the oxidative stress caused by chlorimuron-ethyl.…”