Characterization of Endophytic Streptomyces griseorubens MPT42 and Assessment of Antimicrobial Synergistic Interactions of Its Extract and Essential Oil from Host Plant Litsea cubeba

Abstract

The present study aimed to evaluate the synergistic effects of the crude ethyl acetate extract (CEAE) from endophytic actinomycete MPT42 and essential oil (EO) of the same host plant Litsea cubeba. The isolate MPT42, exhibiting broad-spectrum antimicrobial activities and harboring all three antibiotic-related biosynthetic genes pks-I, pks-II, and nrps, was identified as Streptomycete griseorubens based on an analysis of the morphology, physiology, and 16S rDNA sequence. Minimum inhibitory concentrations (MICs) and the fractional inhibitory concentration index were used to estimate the synergistic effects of various combined ratios between CEAE or antibiotics (erythromycin, vancomycin) and EO toward 13 microbial strains including pathogens. L. cubeba fruit EO, showing the main chemical constituents of 36.0% citral, 29.6% carveol, and 20.5% limonene, revealed an active-low against tested microbes (MICs ≥ 600 μg/mL). The CEAE of S. griseorubens culture exhibited moderate–strong antimicrobial activities against microbes (MICs = 80–600 μg/mL). Analysis of the mechanism of action of EO on Escherichia coli ATCC 25922 found that bacterial cells were dead after 7 h of the EO treatment at 1 MIC (5.5 mg/mL), where 62% cells were permeabilized after 2 h and 3% of them were filament (length ≥ 6 μm). Combinations of CEAE, erythromycin, or vancomycin with EO led to significant synergistic antimicrobial effects against microbes with 4–16 fold reduction in MIC values when compared to their single use. Interestingly, the vancomycin–EO combinations exhibited a strong synergistic effect against five Gram-negative bacterial species. This could assume that the synergy was possibly due to increasing the cell membrane permeability by the EO acting on the bacterial cells, which allows the uptake and diffusion of antimicrobial substances inside the cell easily. These findings in the present study therefore propose a possible alternative to combat the emergence of multidrug-resistant microbes in veterinary and clinics.

Identification and antibacterial evaluation of endophytic actinobacteria from Luffa cylindrica

“…The KUMS-B2 strain had 99.86% similarity to S. griseorubens strain NBRC 12780. S. griseorubens MPT42 has already been isolated as an endophyte from Litsea cubeba 57 . This strain reported to expresses all three biosynthetic genes associated with the antibiotics PKS-I, PKS-II and NRPS and has shown significant antimicrobial activity 57 .…”

“…S. griseorubens MPT42 has already been isolated as an endophyte from Litsea cubeba 57 . This strain reported to expresses all three biosynthetic genes associated with the antibiotics PKS-I, PKS-II and NRPS and has shown significant antimicrobial activity 57 . The antimicrobial properties of this strain have been demonstrated in many studies 58 , 59 .…”

Effectiveness of Augmentative Biological Control of Streptomyces griseorubens UAE2 Depends on 1-Aminocyclopropane-1-Carboxylic Acid Deaminase Activity against Neoscytalidium dimidiatum

“…To determine if ACCD activity had an additional effect, the two indigenous BCA candidates, S. griseorubens UAE2 (ACCD-producer) and S. wuyuanensis UAE1 (non-ACCD producer) were evaluated for their effectiveness against stem canker disease on royal poinciana under greenhouse (Figure 2) and container nursery conditions (Figure 5). Previously, S. griseorubens E44G and MPT42 strains isolated from soils and stems of Litsea cubeba have been identified as strong antagonists possessing broad antifungal activities [80,81].…”

Genomic and physiological traits provide insights into ecological niche adaptations of mangrove endophytic Streptomyces parvulus VCCM 22513

“…All isolates were inoculated on YIM38 medium (glucose 4 g; yeast extract powder 4 g; malt extract powder 5 g; thiamine-HCl, riboflavin, niacin, pyridoxine-HCl, inositol, calcium pantothenate, and p-aminoben-zoic acid, each 0.5 mg; biotin 0.25 mg; pH 7.0 per liter) for 10 days at 30 °C with shaking at 200rpm (Nguyen et al 2019). The biomass was removed by centrifugation while the supernatant was subjected to freeze-drying process.…”