Bioguided isolation, characterization and media optimization for production of Lysolipins by actinomycete as antimicrobial compound against Xanthomonas citri subsp. citri

Antioxidant and Antibacterial Properties of 1,3-Dihydroxy-,2', 2'-Dimethylpyrano-(5,6)-Xanthone from Streptomyces sp. SU84

<b>Background and Objective:</b> The SU84 was isolated from the rhizosphere of <i>Curcuma longa</i> and identified to be <i>Streptomyces</i> sp. via analysis of its 16S rDNA sequence, chemotaxonomy and morphology. This study aimed to isolate major compounds from the extract culture of strain SU84 and evaluate their antibacterial activity. <b>Materials and Methods:</b> The TLC and silica gel column chromatography were used to purify major compounds, elucidate 1,3-dihydroxy-,2',2'-dimethylpyrano-(5,6)-xanthone (compound <b>1</b>) and lupeol (compound <b>2</b>) using mass spectrometry and nuclear magnetic resonance. One new chemical, compound <b>1</b>, was first isolated from microbial sources. Antibacterial, antioxidant and cytotoxic properties of these compounds were carried out. <b>Results:</b> Various bioassays showed that compound <b>1</b> displayed antibacterial property against Gram-positive bacteria, with a minimum inhibitory concentration of 8-32 μg/mL and minimum bactericidal concentration of 32-128 μg/mL. In addition, the purified compounds were tested against normal cell lines using tetrazolium assay. The results did not show cytotoxic property against L929 and Vero cells, with IC₅₀ values of >512.00 μg/mL. Compounds <b>1</b> and <b>2</b> have also antioxidant properties, with IC₅₀ values of 16.67±7.48 and 38.86±8.45 μg/mL, respectively. <b>Conclusion:</b> The findings suggested that compounds of <i>Streptomyces</i> sp. SU84 displayed antibacterial and antioxidant properties without cytotoxic activity. Extensive studies of compound <b>1</b> may be useful for the advancement of improved methods for avoidance, control and management of bacterial infections and metabolic-related free radical contribution.

Actinomycins produced by endophyte Streptomyces sp. GLL-9 from navel orange plant exhibit high antimicrobial effect against Xanthomonas citri susp. citri and Penicillium italicum

BACKGROUND

Citrus canker and citrus blue mold are two severe diseases in citrus plants, which are mainly caused by Xanthomonas citri susp. citri (Xcc) and Penicillium italicum, respectively. The currently widely used pesticides for these two diseases are harmful to human health and the environment. Therefore, searching for novel antimicrobial agents, especially from natural resources, is getting increasing interest.

RESULTS

In this study, the crude extract of Streptomyces sp. GLL-9, an endophyte from a navel orange tree, was found to exhibit excellent antimicrobial effects against Xcc and P. italicum. Bioassay-guided isolation led to the discovery of three actinomycins (Acts), actinomycin X2 (Act-X2 ), actinomycin D (ActD), and actinomycin XOβ (Act-XOβ ). The MIC (minimum inhibitory concentration) values of Act-X2 , ActD, and Act-XOβ were 31.25, 62.50, and 62.50 μg mL-1 against Xcc, respectively, while 62.50 (Act-X2 ) and 125.00 μg mL-1 (ActD) against P. italicum, being better or comparable to the positive controls. The highest yield of Acts was obtained by solid-state fermentation with rice containing 1% L-tryptophan as a culture medium, being 6.03, 3.07, and 1.02 mg g-1 , for Act-X2 , ActD, and Act-XOβ , respectively. The ethyl acetate extract of Streptomyces sp. GLL-9 cultivated under the optimal fermentation conditions (EAE-1) can efficiently control these two citrus diseases by excessively producing reactive oxygen species (ROS) in both pathogens, damaging the cell membranes of P. italicum, and inhibiting the growth of Xcc. In addition, Act-X2 , ActD, and EAE-1 displayed broad-spectrum antifungal activity.

CONCLUSION

EAE-1 and Acts produced by Streptomyces sp. GLL-9 have high potential as novel antimicrobial agents against plant pathogens. © 2023 Society of Chemical Industry.

Identification and antibacterial evaluation of endophytic actinobacteria from Luffa cylindrica

The emergence of antibiotic-resistant bacteria has limited treatment options and led to the untreatable infections, thereby necessitating the discovery of new antibiotics to battel against bacteria. Natural products from endophytic actinobacteria (EA) serve as a reservoir for discovery of new antibiotics. Therefore, the current study focused on the isolation and antibacterial properties of EA isolated from Luffa cylindrica. Six strains were identified using morphological characterization, SEM analyses and 16S rRNA gene sequencing from the roots and leaves of the plant. They were taxonomically classified as Streptomycetaceae family. This is the first report on EA form L. cylindrica. The strains produced a chain of oval, cubed or cylindrical shaped spores with spiny or smooth surfaces. Three strains; KUMS-B3, KUMS-B4 and KUMS-B6 were reported as endophytes for the first time. Fifty percent of isolates were isolated from leaves samples using YECD medium. Our results showed that the sampling time and seasons may affect the bacterial diversity. All six strains had antibacterial activity against at least one of the tested bacteria S. aureus, P. aeruginosa, and E. coli. Among the strains, KUMS-B6 isolate, closely related to S. praecox, exhibited the highest antibacterial activity against both gram-positive and negative bacteria. KUMS-B6, KUMS-B5 and KUMS-B4 isolates strongly inhibited the growth of P. aeruginosa. Interestingly, the strains, isolated from leaves exhibited stronger antagonist activities compared to those isolated from the roots. The study revealed that the isolated strains from Luffa produce a plethora of bioactive substances that are potential source of new drug candidates for the treatment of infections.

Isolation, Biosynthesis, and Biological Activity of Polycyclic Xanthones From Actinomycetes

Natural products from actinomycetes serve as a crucial source of clinical pharmaceuticals, especially antibiotics and anticancer agents. Among them, polycyclic xanthones belong to a growing group of highly oxygenated aromatic polyketides with a xanthone-containing angular hexacyclic framework. These biosynthetically unique small molecules are of great interest due to their wide spectrum of biological activities, especially the remarkable antibacterial activity against gram-positive bacteria and the significant antineoplastic effects toward various cancer cells at nanomolar concentrations. Their complex structures and significant bioactivities have aroused considerable attention in the chemical and biological communities in recent decades. This review covers the isolation, the biosynthesis, and the biological studies toward these structurally complex and biologically active molecules.

Inhibition of the Citrus Canker Pathogen Using a Photosensitizer Assisted by Sunlight Irradiation

Citrus canker, induced by bacterial infection, seriously affects the growth and productivity of citrus around the world and has attracted strong research interest. The current treatment for this disease uses copper salts to inactivate the pathogenic bacteria: Xanthomonas citri subsp. citri (Xcc) strain. However, copper salts may have a negative impact on the environment or plant. In this work, we identify a chemical compound, 2,6-diiodo-1,3,5,7-tetramethyl-8-(P-benzoic acid)-4,4′-difluoroboradiazaindacene (DIBDP), to inactivate the pathogenic Xcc strain (29-1). DIBDP is activated by sunlight and generates reactive oxygen species to kill the bacteria. In order to overcome the degradation of DIBDP under sunlight, an adjuvant agent was identified to limit the photodegradation of DIBDP by forming a photosensitizer complex (PSC). This complex demonstrated significant antimicrobial activity to Xcc 29-1, which was 64-fold more potent than the copper biocides. The antimicrobial efficacy of PSC on citrus leaves infected by Xcc 29-1 also was much stronger than copper agent and, at the same time, the PSC was safe to the host exposed to sunlight. Thus, this PSC is a promising antibacterial agent to control citrus canker disease.

Actinobacteria from Antarctica as a source for anticancer discovery

Although many advances have been achieved to treat aggressive tumours, cancer remains a leading cause of death and a public health problem worldwide. Among the main approaches for the discovery of new bioactive agents, the prospect of microbial secondary metabolites represents an effective source for the development of drug leads. In this study, we investigated the actinobacterial diversity associated with an endemic Antarctic species, Deschampsia antarctica, by integrated culture-dependent and culture-independent methods and acknowledged this niche as a reservoir of bioactive strains for the production of antitumour compounds. The 16S rRNA-based analysis showed the predominance of the Actinomycetales order, a well-known group of bioactive metabolite producers belonging to the Actinobacteria phylum. Cultivation techniques were applied, and 72 psychrotolerant Actinobacteria strains belonging to the genera Actinoplanes, Arthrobacter, Kribbella, Mycobacterium, Nocardia, Pilimelia, Pseudarthrobacter, Rhodococcus, Streptacidiphilus, Streptomyces and Tsukamurella were identified. The secondary metabolites were screened, and 17 isolates were identified as promising antitumour compound producers. However, the bio-guided assay showed a pronounced antiproliferative activity for the crude extracts of Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653. The TGI and LC50 values revealed the potential of these natural products to control the proliferation of breast (MCF-7), glioblastoma (U251), lung/non-small (NCI-H460) and kidney (786-0) human cancer cell lines. Cinerubin B and actinomycin V were the predominant compounds identified in Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653, respectively. Our results suggest that the rhizosphere of D. antarctica represents a prominent reservoir of bioactive actinobacteria strains and reveals it as an important environment for potential antitumour agents.

Solid phase microextraction as a powerful alternative for screening of secondary metabolites in actinomycetes

Actinobacteria are one of the most promising producers of medically and industrially relevant secondary metabolites. However, screening of such compounds in actinobacteria growth demands simple, fast, and efficient extraction procedures that enable detection and precise quantification of biologically active compounds. In this regard, solid phase microextraction (SPME) emerges as an ideal extraction technique for screening of secondary metabolites in bacteria culture due to its non-exhaustive, minimally invasive, and non-destructive nature: its integrated sample preparation workflow; balanced coverage feature; metabolism quenching capabilities; and superior cleanup, as well as its versatility in configuration, which enables automation and high throughput applications. The current work provides a comparison of micro-scale and direct immersion SPME (DI-SPME) for screening of secondary metabolites, describes the optimization of the developed DI-SPME method, and introduces the developed technique for mapping of target secondary metabolites as well as its direct coupling to mass spectrometry for such applications. The optimized DI-SPME method provided higher amounts of extracted ions and intensity signals, yielding superior extraction and desorption efficiency as compared with micro-scale extraction. Studied compounds presented stability on the coating for 24 h at room temperature. The DI-SPME mapping approach revealed that lysolipin I and the lienomycin analog are distributed along the center and edges of the colony, respectively. Direct coupling of SPME to MS provided a similar ions profile as SPME-LC-MS while enabling a significant decrease in analysis time, demonstrating its suitability for such applications. DI-SPME is herein presented as an alternative to micro-scale extraction for screening of secondary metabolites in actinobacteria solid medium, as well as a feasible alternative to DESI-IMS for mapping of biologic radial distribution of secondary metabolites and cell life cycle studies. Lastly, the direct coupling of DI-SPME to MS is presented as a fast, powerful technique for high throughput analysis of secondary metabolites in this medium.