Streptomyces thermoviolaceus SRC3 strain as a novel source of the antibiotic adjuvant streptazolin: A statistical approach toward the optimized production

Antimicrobial sensitisers: Gatekeepers to avoid the development of multidrug-resistant bacteria

The resistance of multidrug-resistant bacteria to existing antibiotics forces the continued development of new antibiotics and antibacterial agents, but the high costs and long timeframe involved in the development of new agents renders the hope that existing antibiotics may again play a part. The "antibiotic adjuvant" is an indirect antibacterial strategy, but its vague concept has, in the past, limited the development speed of related drugs. In this review article, we put forward an accurate concept of a "non-self-antimicrobial sensitisers (NSAS)", to distinguish it from an "antibiotic adjuvant", and then discuss several scientific methods to restore bacterial sensitivity to antibiotics, and the sources and action mechanism of existing NSAS, in order to guide the development and further research of NSAS.

Bioprospecting the potential of metabolites from a Saharan saline soil strain Nocardiopsis dassonvillei GSBS4

Saharan soil samples collected in El-Oued province have been investigated for actinobacteria as a valuable source for the production of bioactive metabolites. A total of 273 isolates were obtained and subjected to antagonistic activity tests against human pathogenic germs. A strain with a broad-spectrum antimicrobial activity was selected and identified as Nocardiopsis dassonvillei GSBS4, with high sequence similarities to N. dassonvillei subsp. dassonvilleiT X97886.1 (99%) based on polyphasic taxonomy approach and 16S ribosomal ribonucleic acid gene sequence analysis. The GSBS4 ethyl acetate crude extract showed strong antibacterial activity towards pathogenic bacteria and Candida albicans. It inhibited biofilm formation by Staphylococcus aureus and methicillin-resistant S. aureus with minimum inhibitory concentrations estimated at 0.144 and 1.15 mg·mL-1 , respectively. A 44% biofilm reduction was obtained for S. aureus and 61% for Pseudomonas aeruginosa. Furthermore, phenols composition of the crude extract showed a significant dose-dependent antioxidant activity by α-diphenyl-β-picrylhydrazyl (57.21%) and 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (64.29%) radicals scavenging assays. Although no inhibition was obtained on human coronavirus human coronavirus (HCoV) 229E and on model enterovirus (poliovirus 1) infection, a dose-dependent increase in cell viability of HCoV 229E-infected cells was noticed as the viability increased from 21% to 37%. Bioassay-guided fractionation of the crude extract gave a fraction showing antibacterial activity, which was analyzed by liquid chromatography-electrospray mass spectrometric technique, providing structural features on a major purple metabolite.

Construction of a fungal consortium for effective degradation of rice straw lignin and potential application in bio-pulping

To improve the lignin degradation efficiency, we established a co-culture consortium (LDFC) consisting of Trametes hirsuta BYL-3, Trametes versicolor BYL-7 and Trametes hirsuta BYL-8. The testing results showed that the constructed consortium showed improved the lignin degradation rate by fungi. The optimal cultivation conditions were mixture at 1:1:1 vol ratio of each fungus, 7% (w/v) of inoculum amount, culture temperature at 26 °C, pH was 6.9 and 10 days of culturing time. Under these conditions, the degradation rate of lignin was 39.7%, which was 9.3% higher than those before optimization (30.4%). Using rice straw for treatment by LDFC to papermaking, the paper tensile strength was 8 N, and the ring pressure index was 2.46 N·m/g, which meets the standards for the production of corrugated paper for packaging. These results indicate that LDFC has potential application value to convert rice straw resources for bio-pulping to make papers.

Actinobacteria Derived from Algerian Ecosystems as a Prominent Source of Antimicrobial Molecules

Actinobacteria, in particular "rare actinobacteria" isolated from extreme ecosystems, remain the most inexhaustible source of novel antimicrobials, offering a chance to discover new bioactive metabolites. This is the first overview on actinobacteria isolated in Algeria since 2002 to date with the aim to present their potential in producing bioactive secondary metabolites. Twenty-nine new species and one novel genus have been isolated, mainly from the Saharan soil and palm groves, where 37.93% of the most abundant genera belong to Saccharothrix and Actinopolyspora. Several of these strains were found to produce antibiotics and antifungal metabolites, including 17 new molecules among the 50 structures reported, and some of these antibacterial metabolites have shown interesting antitumor activities. A series of approaches used to enhance the production of bioactive compounds is also presented as the manipulation of culture media by both classical methods and modeling designs through statistical strategies and the associations with diverse organisms and strains. Focusing on the Algerian natural sources of antimicrobial metabolites, this work is a representative example of the potential of a closely combined study on biology and chemistry of natural products.

Osmanicin, a Polyketide Alkaloid Isolated from Streptomyces osmaniensis CA-244599 Inhibits Elastase in Human Fibroblasts

The strain Streptomyces osmaniensis CA-244599 isolated from the Comoros islands was submitted to liquid-state fermentation coupled to in situ solid-phase extraction with amberlite XAD-16 resin. Elution of the trapped compounds on the resin beads by ethyl acetate afforded seven metabolites, osmanicin (1), streptazolin (2), streptazone C (3), streptazone B₁ (4), streptenol C (5), nocardamine (6) and desmethylenylnocardamine (7). Osmanicin (1) is a newly reported unusual scaffold combining streptazolin (2) and streptazone C (3) through a Diels-Alder type reaction. Experimental evidence excluded the spontaneous formation of 1 from 2 and 3. The isolated compounds were evaluated for their ability to inhibit elastase using normal human diploid fibroblasts. Compound 1 exhibited the most potent activity with an IC₅₀ of 3.7 μM.

Modeling improved production of the chemotherapeutic polypeptide actinomycin D by a novel Streptomyces sp. strain from a Saharan soil

The novel bioactive actinobacterial strain GSBNT10 obtained from a Saharan soil, was taxonomically characterized using a polyphasic approach. 16S rRNA gene sequence analysis supported the classification of the isolate within the genus Streptomyces indicating it as a novel species. The major metabolite responsible of the bioactivity was purified and structurally characterized as actinomycin D (act-D) by mass spectrometric and nuclear magnetic resonance analyses Plackett-Burman design (PBD) and response surface methodology (RSM) were applied in order to optimize the medium formulation for the production of this bioactive metabolite. By PBD experiments, NaNO₃, K₂HPO₄ and initial pH value were selected as significant variables affecting the metabolite production. Central Composite Design (CCD) showed that adjustment of the fermentative medium at pH 8.25, K₂HPO₄ at 0.2 gL^-1 and NaNO₃ at 3.76 gL^-1 were the values suiting the production of act-D. Moreover, the results obtained by the statistical approach were confirmed by act-D detection using the HPLC equipped with a diode array detector and coupled online with electrospray-mass spectrometry (ESIMS) technique. act-D production was highly stimulated, obtaining a good yield (656.46 mgL^-1) which corresponds to a 58.56% increase compared with the non-optimized conditions and data from LC-ESIMS technique efficiently confirmed the forecast from RSM.

The streptazolin- and obscurolide-type metabolites from soil-derivedStreptomyces albonigerYIM20533 and the mechanism of influence of γ-butyrolactone on the growth ofStreptomycesby their non-enzymatic reaction biosynthesis

Eleven new compounds with streptazolin- and obscurolide-type skeletons were isolated from soil-derivedStreptomyces albonigerobtained from Tibet, China.