In this article, we focused on the occurrence and the diversity of actinobacteria from sebkhas using two techniques: cultural and culture-independent (molecular cloning). Therefore, studying the diversity and distribution of actinobacteria in such special environments is important for determining the ecological and biotechnological roles of these microorganisms.
Actinobacteria play an important role in safeguarding the environment by improving plant growth through nitrogen fixation, biodegradation, and bioremediation. Such unexplored ecological niches have been considered by many authors as sources of novel actinobacteria and bioactive molecules. These salt lakes are situated in the east of Algeria and they are microbiologically underexploited. The main purpose of this research is to study the microbial diversity of actinobacteria, living in “Ezzemoul” and “Djendli” sebkhas soils. niger RAF106 and its intracellular enzymes or proteins have a promising potential to be applied commercially in the processing and industry of food and feed to detoxify AFB1. Furthermore, genomic sequence analysis indicated that the fungus was considered to be safe owing to the absence of virulence genes and the gene clusters for the synthesis of mycotoxins. In addition, intracellular enzymes or proteins with excellent thermotolerance were verified as being able to degrade AFB1 into metabolites with low or no mutagenicity. niger RAF106 still degraded AFB1 at initial pH values that ranged from 4 to 10 and at cultivation temperatures that ranged from 25 to 45 ☌. Treatment with yeast extract as a nitrogen source stimulated the degradation, but treatment with NaNO3 and NaNO2 as nitrogen sources and lactose and sucrose as carbon sources suppressed the degradation. In this study, Aspergillus niger RAF106 could effectively degrade AFB1 when cultivated in Sabouraud dextrose broth (SDB) with contents of AFB1 ranging from 0.1 to 4 μg/mL. Microbial degradation is an effective and attractive method for eliminating aflatoxin B1 (AFB1), which is severely toxic to humans and animals. This study provides a novel production strain for compounds 1, 2, 3 and 5, and four potential promising anticancer agents. In addition, compounds 1, 2, 3 and 5 was first found to have the ability to inhibit the invasion and migration of A549 cells (lung cancer cells), which exhibited the potentiality for these compounds to be used as novel anticancer drugs. The minimum inhibitory concentrations (MICs) against Staphylococcus aureus, Klebsiella aerogenes and Proteus vulgaris are 160 µg/mL, 100 µg/mL, 120 µg/mL for the compound 3 and 180 µg/mL, 130 µg/mL 150 µg/mL for the compound 5, respectively. Compounds 3 and 5 exhibit antibacterial activity against Staphylococcus aureus, Klebsiella aerogenes and Proteus vulgaris. Herein, four cyclic dipeptides, namely, cyclo(L-Val-L-Pro) (compound 1), cyclo(L-Pro-L-Leu) (compound 2), cyclo(L-Pro-L-Tyr) (compound 3) and cyclo(L-Pro-L-Phe) (compound 5), and an N-acetyltyramine (compound 4) were first isolated and identified as products of the marine Streptomyces griseorubens f8. Marine actinomycetes are a potential source of a wide variety of bioactive natural products. These findings led us to suggest that these actinobacterial strains could be used as decontamination treatments for the reduction of AFB1 content. Among the latter, strains ACD6 and ABH19 showed no adsorption mechanism involved, suggesting a potential degradation mechanism.
The three most efficient reducers (94.9–97.6%) were two strains belonging to the genus Streptomyces and one to the genus Saccharothrix. AFB1 content was reduced by all strains (42.9–97.6%). After a 4-day incubation at 30☌ on AFB1-supplemented medium (5 ppm of AFB1), AFB1 was extracted and quantified. Secondly, each strain’s efficacy to reduce pure AFB1 content was studied in ISP2-medium. Firstly, morphological study and molecular analysis, based on the 16S rRNA gene, indicated that these strains belong to Actinomadura, Nocardiopsis, Nonomuraea, Saccharothrix and Streptomyces genera. In order to reduce AFB1 occurrence in foodstuffs, 13 strains of mycelial actinobacteria were tested in vitro for the efficacy to reduce AFB1 content all were isolated from the Saharan soils of Algeria.
Aflatoxin B1 (AFB1) is a carcinogenic compound produced by filamentous fungi.
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