Potential Bioactive Compounds from Marine Streptomyces sp. and Their In Vitro Antibiofilm and Antibacterial Activities Against Antimicrobial-Resistant Clinical Pathogens

Diversity of secondary metabolites from marine Streptomyces with potential anti-tubercular activity: a review

The bacterial genus Streptomyces is known for the prolific production of secondary metabolites, which exhibit remarkable structural diversity and potent biological activities. Tuberculosis (TB) remains a formidable global health challenge exacerbated by the emergence of antimicrobial resistance (AMR), necessitating the discovery of novel therapeutic agents. The untapped potential of marine Streptomyces-derived secondary metabolites offers a promising avenue for screening anti-tubercular (anti-TB) compounds with unique chemical structures and potential bioactive properties. The review emphasizes the diverse marine habitats and Streptomyces with novel anti-TB bioactive metabolites. It discusses fermentation and bioprocessing strategies for screening anti-TB drugs. This review also covers the chemical diversity, potency, mechanism of action, and structures of about seventy anti-TB compounds discovered from marine Streptomyces. These compounds span various chemical classes, including quinones, macrolactams, macrolides, phenols, esters, anthracyclines, peptides, glycosides, alkaloids, piperidones, thiolopyrrolones, nucleosides, terpenes, flavonoids, polyketides, and actinomycins. It emphasizes the need to explore marine ecosystems to discover more novel anti-TB natural products.

An Overview of Lsr2 Repressor Effect in Streptomyces spp. Secondary Metabolism

The genus Streptomyces is one of the largest producers of secondary metabolites with bioactive properties of interest. However, many of the genes involved in synthesizing these compounds are silenced under laboratory conditions. One of the strategies used to activate these metabolic pathways is the elimination of repressor genes, which prevent the transcription of other genes. In this work, the lsr2 gene has been selected for study since it is a repressor with a preference for binding to AT-rich regions, which makes it exert its effect especially on those horizontally transferred gene sequences that have a very different GC content to the core Streptomyces spp. genome. Therefore, the effects of the deletion of this gene are observed, and, in addition, a mapping of the potential binding sites of Lsr2 in Streptomyces spp. genomes is proposed. As a result of this gene knockout, the production of various secondary metabolites is overproduced and/or activated, which suggests that the study of this regulator can be interesting in the field of natural product discovery.

Probiotic potential of Streptomyces levis strain HFM-2 isolated from human gut and its antibiofilm properties against pathogenic bacteria

BACKGROUND

Antimicrobial resistance (AMR) is a serious worldwide public health concern that needs immediate action. Probiotics could be a promising alternative for fighting antibiotic resistance, displaying beneficial effects to the host by combating diseases, improving growth, and stimulating the host immune responses against infection. This study was conducted to evaluate the probiotic, antibacterial, and antibiofilm potential of Streptomyces levis strain HFM-2 isolated from the healthy human gut.

RESULTS

In vitro antibacterial activity in the cell-free supernatant of S. levis strain HFM-2 was evaluated against different pathogens viz. K. pneumoniae sub sp. pneumoniae, S. aureus, B. subtilis, VRE, S. typhi, S. epidermidis, MRSA, V. cholerae, M. smegmatis, E. coli, P. aeruginosa and E. aerogenes. Further, the ethyl acetate extract from S. levis strain HFM-2 showed strong biofilm inhibition against S. typhi, K. pneumoniae sub sp. pneumoniae, P. aeruginosa and E. coli. Fluorescence microscopy was used to detect biofilm inhibition properties. MIC and MBC values of EtOAc extract were determined at 500 and 1000 µg/mL, respectively. Further, strain HFM-2 showed high tolerance in gastric juice, pancreatin, bile, and at low pH. It exhibited efficient adhesion properties, displaying auto-aggregation (97.0%), hydrophobicity (95.71%, 88.96%, and 81.15% for ethyl acetate, chloroform and xylene, respectively), and showed 89.75%, 86.53%, 83.06% and 76.13% co-aggregation with S. typhi, MRSA, S. pyogenes and E. coli, respectively after 60 min of incubation. The S. levis strain HFM-2 was susceptible to different antibiotics such as tetracycline, streptomycin, kanamycin, ciprofloxacin, erythromycin, linezolid, meropenem, amikacin, gentamycin, clindamycin, moxifloxacin and vancomycin, but resistant to ampicillin and penicillin G.

CONCLUSION

The study shows that S. levis strain HFM-2 has significant probiotic properties such as good viability in bile, gastric juice, pancreatin environment, and at low pH; proficient adhesion properties, and antibiotic susceptibility. Further, the EtOAc extract of Streptomyces levis strain HFM-2 has a potent antibiofilm and antibacterial activity against antibacterial-resistant clinical pathogens.

Identification of potent anti-Candida metabolites produced by the soft coral associated Streptomyces sp. HC14 using chemoinformatics

Candida albicans is the most common pathogen responsible for both spontaneous and recurrent candidiasis. The available treatment of Candida infections has several adverse effects, and the development of new drugs is critical. The current study looked at the synthesis of anti-Candida metabolites by Streptomyces sp. HC14 recovered from a soft coral. Using the Plackett Burman design, the medium composition was formulated to maximize production. Using GC-MS, the compounds have been identified, and a cheminformatics approach has been used to identify the potential source of activity. The compounds that showed high potential for activity were identified as pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro-3-(phenylmethyl)-3 and di-n-octyl based on their docking score against the cytochrome monooxygenase (CYP51) enzyme in Candida albicans. As a result of their discovery, fewer molecules need to be chemically synthesized, and fermentation optimization maximizes their synthesis, providing a strong foundation for the development of novel anti-Candida albicans agents.

3-Hydroxy coumarin demonstrates anti-biofilm and anti-hyphal efficacy against Candida albicans via inhibition of cell-adhesion, morphogenesis, and virulent genes regulation

Candida albicans, a common fungus of human flora, can become an opportunistic pathogen and causes invasive candidiasis in immunocompromised individuals. Biofilm formation is the prime cause of antibiotic resistance during C. albicans infections and treating biofilm-forming cells is challenging due to their intractable and persistent nature. The study intends to explore the therapeutic potential of naturally produced compounds by competitive marine bacteria residing in marine biofilms against C. albicans biofilm. To this end, 3-hydroxy coumarin (3HC), a compound identified from the cell-free culture supernatant of the marine bacterium Brevundimonas abyssalis, was found to exhibit anti-biofilm and anti-hyphal activity against both reference and clinical isolates of C. albicans. The compound demonstrated significant inhibitory effects on biofilms and impaired the yeast-to-hyphal transition, wrinkle, and filament morphology at the minimal biofilm inhibitory concentration (MBIC) of 250 µg mL^-1. Intriguingly, quantitative PCR analysis of 3HC-treated C. albicans biofilm revealed significant downregulation of virulence genes (hst7, ume6, efg1, cph1, ras1, als1) associated with adhesion and morphogenesis. Moreover, 3HC displayed non-fungicidal and non-toxic characteristics against human erythrocytes and buccal cells. In conclusion, this study showed that marine biofilms are a hidden source of diverse therapeutic drugs, and 3HC could be a potent drug to treat C. albicans infections.

Evaluation of antimicrobial activity of Streptomyces pactum isolated from paddy soils and identification of bioactive volatile compounds by GC-MS analysis

The objective of this study was to isolate Streptomyces sp. from north paddy soils of Iran and investigation and identification of the bioactive compounds by carrying out GC-MS analysis. Antimicrobial activity was investigated by well diffusion agar technique against the pathogenic microorganisms including Enterococcus faecalis ATCC 29212, Micrococcus luteus ATCC 4698, Bacillus cereus ATCC 11778, Staphylococcus aureus ATCC 9144, Pseudomonas aeruginosa ATCC 27853, Proteus mirabilis ATCC 43071. Based on the results of gene sequencing of gene 16S rRNA and phylogenetic analysis, the isolated sample belongs to the genus Streptomyces with the highest degree of resemblance (99/87%) to the Streptomyces pactum strain ACT12. The isolate showed a broad spectrum of antibacterial activity against test microorganisms. This isolate showed maximum antibacterial activity against M. luteus (25 ± 0.5 mm) and the most resistant microorganism against antibacterial activity of this isolate was P. aeruginosa (9 ± 0.5 mm). The contact bioautography method was used to detect compounds that were responsible for antimicrobial activity and showed the active compounds with R_f values of 0.8-0.9. The identification of bioactive metabolites were performed using gas chromatography-mass spectrometry (GC-MS). GC-MS analysis of the extract showed the presence of 15 volatile compounds. The main compounds were Methyl-3-(3,5-ditertbutyl-4-hydroxyphenyl) (10.88%) and Dibutyl phthalate (8.34%) in comparison with other bioactive compounds. The results showed that north paddy soils of Iran are a rich source of microbial flora for the production of antimicrobial compounds and useful for antimicrobial compounds discovery from Streptomyces sp.

Evaluation of Green Silver Nanoparticles Fabricated by Spirulina platensis Phycocyanin as Anticancer and Antimicrobial Agents

Green nanotechnology has attracted attention worldwide, especially in treating cancer and drug-resistant section 6 microbes. This work aims to investigate the anticancer activity of green silver nanoparticles synthesized by Spirulina platensis phycocyanin (SPAgNPs) on two cancer cell lines: Lung cancer cell line (A-549) and breast cancer cell line (MCF-7), compared to the normal human lung cell line (A138). We also aimed to investigate the bactericidal activity against Staphylococcus aureus ATCC29737, Bacillus cereus ATCC11778, Escherichia coli ATCC8379, and Klebsiella pneumonia, as well as the fungicidal activity against Candida albicans (ATCC6019) and Aspergillus niger. The obtained SPAgNPs were spherical and crystalline with a size of 30 nm and a net charge of -26.32 mV. Furthermore, they were surrounded by active groups responsible for stability. The SPAgNPs scavenged 85% of the DPPH radical with a relative increase of approximately 30% over the extract. The proliferation of cancer cells using the MTT assay clarified that both cancer cells (A-549 and MCF-7) are regularly inhibited as they grow on different concentrations of SPAgNPs. The maximum inhibitory effect of SPAgNPs (50 ppm) reached 90.99 and 89.51% against A-549 and MCF7, respectively. Regarding antimicrobial activity, no inhibition zones occurred in bacterial or fungal strains at low concentrations of SPAgNPs and the aqueous Spirulina platensis extract. However, at high concentrations, inhibition zones, especially SPAgNPs, were more potent for all tested microorganisms than their positive controls, with particular reference to Staphylococcus aureus, since the inhibition zones were 3.2, 3.8, and 4.3 mm, and Bacillus cereus was 2.37 mm when compared to tetracycline (2.33 mm). SPAgNPs have more potent antifungal activity, especially against Aspergillus niger, compared to their positive controls. We concluded that SPAgNPs are powerful agents against oxidative stress and microbial infection.