Isolation and extraction of some compounds that act as antimicrobials from actinomycetes

In-silico and in-vitro evaluation of antifungal bioactive compounds from Streptomyces sp. strain 130 against Aspergillus flavus

Streptomyces spp. are considered excellent reservoirs of natural bioactive compounds. The study evaluated the bioactive potential of secondary metabolites from Streptomyces sp. strain 130 through PKS-I and NRPS gene-clusters screening. GC-MS analysis was done for metabolic profiling of bioactive compounds from strain 130 in the next set of experiments. Identified antifungal compounds underwent ADMET analyses to screen their toxicity. All compounds' molecular docking was done with the structural gene products of the aflatoxin biosynthetic pathway of Aspergillus flavus. MD simulations were utilized to evaluate the stability of protein-ligand complexes under physiological conditions. Based on the in-silico studies, compound 2,4-di-tert butyl-phenol (DTBP) was selected for in-vitro studies against Aspergillus flavus. Simultaneously, bioactive compounds were extracted from strain 130 in two different solvents (ethyl-acetate and methanol) and used for similar assays. The MIC value of DTBP was found to be 314 µg/mL, whereas in ethyl-acetate extract and methanol-extract, it was 250 and 350 µg/mL, respectively. A mycelium growth assay was done to analyze the effect of compounds/extracts on the mycelium formation of Aspergillus flavus. In agar diffusion assay, zone of inhibitions in DTBP, ethyl-acetate extract, and methanol extract were observed with diameters of 11.3, 13.3, and 7.6 mm, respectively. In the growth curve assay, treated samples have delayed the growth of fungi, which signified that the compounds have a fungistatic nature. Spot assay has determined the fungal sensitivity to a sub-minimum inhibitory concentration of antifungal compounds. The study's results suggested that DTBP can be exploited for antifungal-drug development.Communicated by Ramaswamy H. Sarma.

Silene uniflora Extracts for Strawberry Postharvest Protection

Halophytes are gaining considerable attention due to their applications in saline agriculture, phytoremediation, medicine, and secondary metabolite production. This study investigated the bioactive components present in Silene uniflora (sea campion) hydromethanolic extract, and their antimicrobial activity was evaluated both in vitro and ex situ against two strawberry phytopathogens, namely Botrytis cinerea (grey mold) and Colletotrichum nymphaeae (anthracnose fruit rot). The main identified phytochemicals were mome inositol, saturated fatty acid esters, and cyclotetracosane. In vitro tests demonstrated complete inhibition of the growth of B. cinerea and C. nymphaeae at extract concentrations of 1000 and 1500 μg·mL^-1, respectively, with an activity comparable to that of fosetyl-Al and substantially higher than that of azoxystrobin. This activity was improved upon conjugation with chitosan oligomers (COS), yielding inhibition values of 750 and 1000 μg·mL^-1. The COS-S. uniflora conjugate complexes were then tested as protective treatments for postharvest storage of strawberry fruit, resulting in high protection against artificially inoculated B. cinerea and C. nymphaeae at doses of 3750 and 5000 μg·mL^-1, respectively. The reported results open the door to the valorization of this halophyte as a source of biorationals for strawberry protection.

Isolation, Identification and Screening of Saharan Actinomycete Strain Streptomyces fimbriatus AC31 Endowed with Antimicrobial Activity

The increasing global public health concern of antimicrobial resistance (AMR) necessitates exploration of natural antimicrobial agents as potential alternatives. This study aimed to investigate antimicrobial activities of Saharan actinomycetes, with specific focus on the strain Streptomyces fimbriatus AC31, that holds promising potential as an alternative to combat AMR. In this context, 32 actinomycetes were isolated from El Atteuf (Ghardaïa), Algeria. Isolates obtained were characterized morphologically and biochemically. Screened isolate was identified by 16S rRNA gene sequencing. Classification of actinomycete isolates was carried out by UPGMA (Unweighted Pair Group Method with Arithmetic Mean). Then, they were screened for their antimicrobial activity by cross-streak method. Identification of 32 isolates revealed 5 genera: Streptomyces (65.63%), Nocardia (9.38%), Streptosporangium (9.38%), Nocardiopsis (9.38%) and Actinomadura (6.25%). According to the biochemical and physiological characteristics, UPGMA classified the isolates in 4 phenons. A number of 24 (75.00%) isolates were active against Gram-positive bacteria, 21 (65.63%) isolates were effective against Gram-negative bacteria, and 25 (78.13%) isolates inhibited Candida albicans. Screened strain Streptomyces fimbriatus AC31 showed highest antagonistic activity and revealed an inhibition zones of 41, 38, 41, 42, and 44 mm, against B. subtilis (ATCC 6633), E. coli (ATCC 8739), S. typhimurium (ATCC 13331), S. aureus (ATCC 6538) and C. albicans (ATCC 10231), respectively. Phylogenetic identification of the AC 31 isolate using 16S rRNA gene sequence showed similarity of 100% with Streptomyces fimbriatus NBRC 15411T. Actinomycete isolates characterized in this study were endowed with antimicrobial activity against various pathogenic microorganisms that could be used efficiently in developing new antimicrobial substances.