Antiproliferative and antimicrobial compounds from Streptomyces levis: supported by in vitro and in silico molecular docking approach.

The present work describes the investigation of secondary metabolites produced by rhizospheric soil isolate Streptomyces levis with respect to partial purification, bioactivity, structural elucidation, and docking study. MIC (Minimum Inhibitory Concentration) of the fraction was found to be 16 µg/mL, 32 µg/mL, and 8 µg/mL against S. aureus, E. coli, and C. albicans respectively. The fraction exhibited an IC50 of 90.48 µg/mL and 59.10 µg/mL against L929 and HeLa cell lines respectively. Spectroscopic analysis showed abundant of Isofucosterol 3-O-[6-O-(9-Octadecanoyl)-b-D-glucopyranoside], and Viniferal. These compounds were docked against receptor molecules E6, E7, Caspase-3, and Bcl2. The in-silico results suggested that all the secondary metabolites showed higher docking scores than the standard compound 5-Fluorouracil. Molecular docking study and published literature suggested that Isofucosterol 3-O-[6-O-(9-Octadecanoyl)-b-D-glucopyranoside] inactivated viral oncoprotein E7 and arrested the cell cycle from entering in S phase. Viniferal induced apoptosis by inactivation of Bcl2.

Rare actinobacteria: a potential source of bioactive polyketides and peptides.

Polyketides and peptides obtained from actinobacteria are important therapeutic compounds which include front line antibiotics and anticancer drugs. Many screening programs are directed towards isolation of bioactive compounds from these organisms but the chances of finding novel antimicrobial leads among common actinobacteria are fast dwindling. As a result, the focus has shifted to the members of less exploited genera of rare actinobacteria. Three isolates, MMS8, MMS16 and KCR3 found to be potent polyketide and peptide producers were identified by 16S rRNA gene sequencing and their sequences deposited in the GenBank under the accession numbers MG407702, MG372012 and MG430204 respectively. MMS8 identified as Micromonospora auratinigra, yielded one potent compound determined to be chloroanthraquinone with an minimum inhibitory concentration (MIC) of 8 µg/ml against Bacillus subtilis and an IC50 value of 10 µg/ml and 4 µg/ml against HeLa and IMR cell lines respectively. This is the first report of the production of chloroanthraquinone by M. auratinigra. MMS16, identified as a member of the family Micromonosporaceae, yielded a potent compound MMS16B analyzed to be a novel bafilomycin analogue. The MIC of the compound was found to be 7 µg/ml against B.subtilis and IC50 value against HeLa and IMR was observed to be 9 µg/ml and 14 µg/ml respectively. MMS16B was also found to exhibit anti-quorum sensing (AQS) activity at sublethal concentrations. KCR3 identified as Kocuria kristinae yielded a novel antimicrobial peptide with antibacterial, antifungal and AQS activity. To the best of our knowledge, no antimicrobial activity has ever been reported from K. kristinae.

Culturable rare actinomycetes from Indian forest soils: Molecular and physicochemical screening for biosynthetic genes.

BACKGROUND AND OBJECTIVES: Rare actinomycetes are a promising source of novel metabolites of pharmaceutical importance. The current study focussed on selective isolation of specific genera of rare actinomycetes and screening the isolates for biosynthetic genes particularly polyketide synthases (PKS) and non ribosomal peptide synthetases (NRPS). MATERIALS AND METHODS: The soil samples were subjected to various pre-treatments like 1.5% phenol treatment, 0.3% chloramine T treatment, benzethonium chloride treatment, etc. and plated on selective media supplemented with specific antibiotics targeting rare genera of actinomycetes. The putative rare actinomycete isolates were screened for bioactivity using agar cross streak method and agar well diffusion method. The ability of the isolates to produce anti-quorum sensing compounds was tested against Serratia marcescens. The isolates were also screened for the presence of biosynthetic gene clusters associated with PKS-I, PKS-II and NRPS pathways using the degenerate primer sets K1F-M6R, KSα/KSß and A3FA7R, respectively. The expression of these gene clusters was tracked by physicochemical screening of the extracts of isolates using spectroscopic and chromatographic techniques. RESULTS: In this study, 1.5% phenol treatment was found to be the most promising followed by heat treatment and chloramine treatment. Our studies showed that ISP5 agar was the best for isolation of rare genera followed by ISP7, Starch Caesin agar and ISP2 supplemented with antibiotics like gentamicin, nalidixic acid and streptomycin. Micromonospora was the most abundant genus followed by Dactylosporangium. Actinomadura, Nocardiopsis and Actinoplanes were almost equal in number. Primary screening showed that 92% of the isolates were active against one of the test organisms. Thirty seven isolates were found to produce anti-quorum sensing (QS) compounds. NRPS sequences were detected in thirty nine isolates (42.8%), whereas PKS-I and PKS-II sequences were detected in seventeen and twenty eight strains (18.6% and 30.7%), respectively. CONCLUSION: Nine type I and type II polyketide-producing isolates as well as six peptide-producing isolates were found. The peptide extract of isolate KCR3 and a polyketide extract of isolate NCD10 were found to possess anti-tumor activity exhibiting an IC50 value of 3 µg/ml and 2.5 µg/ml against HeLa cells.

Novel aromatic polyketides from soil Streptomyces spp.: purification, characterization and bioactivity studies.

Aromatic polyketides are important therapeutic compounds which include front line antibiotics and anticancer drugs. Since most of the aromatic polyketides are known to be produced by soil dwelling Streptomyces, 54 Streptomyces strains were isolated from the soil samples. Five isolates, R1, B1, R3, R5 and Y8 were found to be potent aromatic polyketide producers and were identified by 16S rRNA gene sequencing as Streptomyces spectabilis, Streptomyces olivaceus, Streptomyces purpurascens, Streptomyces coeruleorubidus and Streptomyces lavendofoliae respectively. Their sequences have been deposited in the GenBank under the accession numbers KF468818, KF681280, KF395224, KF527511 and KF681281 respectively. The Streptomyces strains were cultivated in the media following critically optimised culture conditions. The resulting broth extracts were fractionated on a silica gel column and preparative TLC to obtain pure compounds. The pure compounds were tested for bioactivity and the most potent compound from each isolate was identified by UV-Vis, IR and NMR spectroscopic methods. Isolated S. spectabilis (R1), yielded one potent compound identified as dihydrodaunomycin with an MIC of 4 µg/ml against Bacillus cereus and an IC50 value of 24 µM against HeLa. S. olivaceus (B1), yielded a comparatively less potent compound, elloramycin. S. purpurascens (R3) yielded three compounds, rhodomycin, epelmycin and obelmycin. The most potent compound was rhodomycin with an MIC of 2 µg/ml against B. cereus and IC50 of 15 µM against HeLa. S. coeruleorubidus (R5), yielded daunomycin showing an IC50 of 10 µM and also exhibiting antimetastatic properties against HeLa. S. lavendofoliae (Y8), yielded a novel aclacinomycin analogue with IC50 value of 2.9 µM and potent antimetastatic properties at 1 µM concentration against HeLa. The study focuses on the characterization of aromatic polyketides from soil Streptomyces spp., which can serve as potential candidates for development of chemotherapeutic drugs in future.

Antibacterial effects of hybrid tooth colored restorative materials against Streptococcus mutans: An in vitro analysis.

OBJECTIVE: The objective of this study was to evaluate the antibacterial effect of two hybrid restoratives, namely resin modified glass ionomer cement (GC Fuji II™ LC, GC Corporation, Tokyo, Japan) and giomer (Beautifil-II, Shofu Inc., Kyoto, Japan) against Streptococcus mutans [Microbial Type Culture Collection (MTCC), 890]. MATERIALS AND METHODS: The antibacterial effect was evaluated using an agar diffusion test. The prepared wells in petri dishes were completely filled with chlorhexidine (positive control group), resin modified glass ionomer cement and giomer respectively. Prepared bacterial suspension was poured over the petri dish and was spread evenly using the plate spreader. The culture plates were placed in the incubator for 24 h at 37°C. The antibacterial activity was evaluated after 24 h, 48 h, and 7 days for each group in triplicates. RESULTS AND CONCLUSION: The results of the antibacterial effect of the tested materials were collected, statistically analyzed using the ANOVA test to determine the difference between the mean diameters of the inhibition zone produced. The mean zone of bacterial inhibition was found to be more with the giomer specimens at all time periods. However, this inhibitory activity showed a gradual decrease over a period of 7 days and the maximum inhibition was evident after 24 h with both the test materials.