Plant growth promoting endophytic Pseudomonas aeruginosa RD10 isolated from water hyacinth for phenol degradation
Authors: S Reena Mol , Murugesan A.G. 
Published: January 2023

A total of twelve endophytic bacteria were isolated from the root of E. crassipes. All these bacterial strains were analyzed for phenol degradation potential. Twelve endophytic bacteria were subjected to polyphenol resistance analysis and all showed phenol tolerance up to 300 ppm. Among the twelve bacterial strains, the strain RD10 was resistant up to 800 ppm, and reduced growth were observed at higher concentrations. The plant growth-promoting properties of endophytic bacterial strains were analyzed. Among the isolated bacterial strain, only five strains produced ACC deaminase. IAA production was detected in seven bacterial isolates, while siderophore production was determined from only five bacterial strains. Among the isolated endophytes, the strain RD10 exhibited ACC deaminase, IAA, and siderophore activity in submerged fermentation. ACC deaminase production of 125.2 ± 4.8 m/ml was shown by strain RD10 and IAA production was 89.7 ± 5.1 μg/ml. Moreover, maximum siderophore production was observed (53.9 ± 4.9% siderophore units) in strain RD3. Catechol 2,3-dioxygenase activity of the bacterial strains was analyzed. Catechol 2,3 dioxygenase activity ranges from 0.03 ± 0.01 U/mg to 35.2 ± 1.1 U/mg. Phenol degradation by the isolated endophytes was studied and the initial phenol concentration was 500 ppm. The strain RD1 degraded 1.2 ± 0.2% phenol and more than 50% phenol degradation was observed in strains RD3, RD4, RD6, RD7, RD9, RD10, and RD11, respectively. The endophytic bacterial strain was Gram-negative, rodshaped and motile. It was non-spore-forming bacteria, capsulated and, showed a positive reaction to oxidase and catalase. In MacConkey agar medium, strain RD10 forms smooth and flat colonies, and the diameter of the colonies ranged from 2 to 3 mm. The colonies have an alligator skin-like appearance on top view and have regular margins. The strain RD10 was streaked on blood agar medium and the strain RD10 produced strong pigmentation on blood agar. Antibiotic sensitivity of strain RD10 against various antibiotics in terms of zone of inhibition was analyzed. The endophytic strain RD10 was sensitive to all selected antibiotics. Based on biochemical characters, pigment analysis and, molecular characterization, the strain was confirmed as P. aeruginosa RD10. In this study, P. aeruginosa RD10 was cultured at 400, 500 and, 600 mg/l phenol concentration for 96 h. Optimum growth was achieved at 500 mg/l concentration and an inhibitory effect was observed at 600 mg/l phenol concentration. The results confirmed that the selected strain can withstand and grow well at 500 mg/l phenol concentration. The strain RD10 was cultured at various incubation temperatures with 500 mg/l phenol concentration. Optimization of environmental factors can lead to maximum degradation of phenol. The results revealed that phenol degradation was influenced by temperature. The highest phenol degradation was achieved at 30 °C in Erlenmeyer flask culture and decreased at high temperatures. P. aeruginosa RD10 could degrade phenol at pH 5.5 (10.2 ± 0.5% removal), at pH 6.0, 15.4 ± 1.1% of the phenol was degraded after incubation for 72 h at 30 °C. Phenol removal (%) declined to 70.4 ± 2.9% at higher initial pH value (9.0).