Microbiological and molecular studies of actinomycetes isolated from algerian bee pollen

Abstract

This study aimed to isolate actinomycetes from some bee pollen samples collected from different Algerian places and evaluate their applications. First, the microbiological quality control of bee pollen samples was investigated, where the analyses showed a microbial load ranged from 7.70 x 102 to 1.93 x 106 CFU/g for the aerobic mesophilic bacteria and from 1.10 x 103 to 5.30 x 105 CFU/g for the anaerobic mesophilic bacteria. Molds and yeasts content varied from 2.70 x 103 to 3.70 x 103 CFU/g. The maximum concentrations for total coliforms and S. aureus were 1.73 x 104 CFU/g and 2.33 x 102 CFU/g, respectively. Sulfite-reducing Clostridium was detected only in one sample. In addition, Salmonella sp. was not detected in all samples. Furthermore, 33 strains of actinomycetes were isolated,characterized, screened to produce extracellular enzymes as well as for antimicrobial activity,and then classified by the UPGMA method. The isolated strains showed eight diversified clusters, where most of them were able to produce extracellular hydrolytic enzymes, including proteases, amylases, and lipases, while only five strains demonstrated significant antimicrobial activity. The crude ethyl acetate extract of the Streptomyces sp. BPA-6 strain was selected to assess its ability to kill or inhibit the growth and reproduction of some pathogens and to analyze and identify its bioactive compounds. The agar-well diffusion method showed that it was only effective against Staphylococcus aureus ATCC 6538P, Bacillus subtilis ATCC 6633, and Candida albicans ATCC 10231, with inhibition zones of 42.33 ± 3.79 mm, 41.66 ± 3.51 mm, and 48.67 ± 2.08 mm, espectively. The recorded MIC value was 62.5 µg/mL against S. aureus ATCC 6538P and B. subtilis ATCC 6633, while it was 250 µg/mL against C. albicans ATCC 10231. Also, the best MMC value was observed against B. subtilis ATCC 6633, with a value of 1000 µg/mL. The GC-MS analyses revealed many antimicrobial compounds, including hexadecanoic acid, 9,12-octadecadienoic acid, and 9-octadecenoic acid. On the other hand, the red pigment of the Streptomyces sp. A23 strain was used for the green synthesis of silver nanoparticles (AgNPs), evaluating their antimicrobial, anticancer, and neuroprotective activities. Good antimicrobial activity was observed against Enterococcus faecalis ATCC 19433, C. albicans ATCC 10231, S. aureus ATCC 6538P, Pseudomonas aeruginosa ATCC 27853, B. subtilis ATCC 6633, Klebsiella pneumoniae ATCC 13883, and Escherichia coli ATCC 7839, with inhibition zones of 32 mm,30 mm, 30 mm, 27 mm, 25 mm, 20 mm, and 19 mm, respectively. The lowest MIC and MBC were recorded against B. subtilis ATCC 6633 with a value of 62.5 µg/mL. Intriguingly, the most of synthesized AgNPs at concentrations of 2 µg/mL, 4 µg/mL, and 8 µg/mL had cytotoxic effects on SH-SY5Y neuroblastoma cell lines. In addition, AgNPs (1 mM, pH 7) exhibited significant neuroprotective activity at the lowest tested concentration.