Isolation of Culturable Endophytic Bacteria from the Roots of Aloe Vera L. (Aloe Barbadensis Miller) and Their Application in Phytodegradation of Xenobiotics

Plant-endophyte interaction is a promising area that needs to be researched for effective contaminant remediation. Aloe barbadensis Miller, also known as Aloe vera, was utilized to isolate, identify, and characterize bacterial endophytes using morphological, biochemical, and molecular techniques. From an A. barbadensis Miller root sample, six distinct endophytic bacterial isolates were tested by morphological and biochemical techniques and also characterized respectively. Using the molecular identification approach of 16S rRNA partial gene sequencing, one of the bacterial isolates was identified. The sequence alignment of isolate AM1 showed the similarity in a range of 99-100% in BLAST with different strains of Bacillus. AM1 isolates exhibited the evidence of antibiotic susceptibility, with a minimum inhibitory concentration (MIC) IC₅₀ value against clarithromycin of concentration 1.5 g/mL. The bacterial isolate was susceptible to clarithromycin, erythromycin, ampicillin, and azithromycin but resistant to amoxicillin and tetracycline. The extract and isolate showed 40 to 85% of increasing inhibition in DPPH and ABTS scavenging activities with concentrations ranging between 0.5 and 2.5 mg/ml. The decolorization and degradation efficiency of synthetic dyes Congo red (CR) and Bromophenol blue (BPB) was studied using endophyte bacterial isolate AM1. The biodegradation of CR and BPB was 79% for 8 ppm and 65% for 2 ppm after 192 h of incubation at room temperature with constant pH (7.0). The degradation and the metabolic products formed during the degradation were predicted using Fourier transform infrared (FTIR) spectroscopy. Significant vanadium accumulation was seen in the leaves, roots, and soil remnants of B. juncea plants grown in symbiosis with endophytic bacteria AM1 through High-performance liquid chromatography (HPLC) analysis. This accumulation may be related to AM1 bacteria with effective root colonization. These findings highlight the efficiency of endophytic bacteria in promoting the remediation of xenobiotics and caveat to the involvement of the AM1 isolate in vanadium assimilation within the roots and rhizosphere of plants.

Graphical Abstract