Background: Actinobacteria is as a group of advanced filamentous bacteria. Rare Actinobacteria are of special interest as they are rarely isolated from the environments. They are a major source of important bioactive compounds. Determining the proper strategy for the identification of Actinobacteria harboring biosynthetic gene clusters and producing bioactive molecules is a challenging platform. Methodology: In this review, we discuss a consequence of microbiological and molecular methods for the identification of rare Actinobacteria. In addition to that, we shed light on rare Actinobacteria's significance in antibiotic production. We also clarified molecular approaches for the manipulation of novel biosynthetic gene clusters via PCR screening, fosmid libraries, and Illumina whole-genome sequencing in combination with bioinformatics analysis. Conclusion: Perceptions of the conventional and molecular identification of Actinobacteria were conducted. This will open the door for the genetic manipulation of novel antibiotic gene clusters in heterologous hosts. Also, these conclusions will lead to constructing new bioactive molecules via genetically engineering biosynthetic pathways.

A distinct strain named Micromonospora sp. Rc5 was isolated from Sinai desert of Egypt and recorded high antagonistic activities against some food and bloodborne pathogens. Morphological and chemotaxonomy characterization confirmed that this isolate belongs to genus Micromonospora. Sequencing of partial 16S rDNA and BLASTN showed that isolate Rc5 is identical to Micromonospora haikouensis (99%) but with low bootstrap value in NJ phylogenetic tree. Comprehensive optimization of several growth factors was performed including initial pH, incubation periods, and different sources of carbon and nitrogen. The highest yield of antimicrobial agent production was obtained after 8 days of incubation at 30°C, pH 6.0, 3 x 10 5 CFU/ml in soya bean meal broth media with agitation of 150 rpm. A dramatic proportional decrease occurred with Original Research Article

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Background Antibiotic resistance is on the rise, and new antibiotic research has slowed in recent years, necessitating the discovery of possibly novel microbial resources capable of producing bioactive compounds. Microbial infections are gaining resistance to existing antibiotics, emphasizing the need for novel medicinal molecules to be discovered as soon as possible. Because the possibilities of isolating undiscovered actinomycetes strains have decreased, the quest for novel products has shifted to rare actinomycetes genera from regular environments or the identification of new species identified in unusual habitats. Main body of the abstract The non-streptomyces actinobacteria are known as rare actinomycetes that are extremely difficult to cultivate. Rare actinomycetes are known to produce a variety of secondary metabolites with varying medicinal value. In this review, we reported the diversity of rare actinomycetes in several habitat including soil, plants, aquatic environment, caves, insects and extreme environments. We also reported some isolation methods to easily recover rare Actinobacteria from various sources guided with some procedures to identify the rare Actinobacteria isolates. Finally, we reported the biosynthetic potential of rare actinomycetes and its role in the production of unique secondary metabolites that could be used in medicine, agriculture, and industry. These microbial resources will be of interest to humanity, as antibiotics, insecticides, anticancer, antioxidants, to mention but a few. Short conclusion Rare actinomycetes are increasingly being investigated for new medicinal compounds that could help to address existing human health challenges such as newly emerging infectious illnesses, antibiotic resistance, and metabolic disorders. The bioactive secondary metabolites from uncommon actinomycetes are the subject of this review, which focuses on their diversity in different habitats, isolation, identification and biosynthetic potentials.

Background: Antibiotic resistance occurs rapidly and naturally. However, the misuse of antibiotics is accelerating the process. And therefore, exploring new antibiotics has been a great demand in order to save people's life. Actinobacteria have been the major source of antibiotics. In this study, we focused on rare types of actinobacteria which are hard to isolate from the environment by traditional methods. Fifty rare actinobacteria were isolated from Egyptian soils, and they were screened against some bacterial pathogens (Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 10145, Klebsiella pneumonia CCM 4415, Streptococcus mutans ATCC 25175, Escherichia coli O157:H7 ATCC 51659, and Salmonella enterica ATCC 25566). Illumina whole genome sequencing was performed for potent isolates. The whole genomes of selected rare actinobacteria were investigated via bioinformatics analysis using neighbor-joining phylogenetic analysis and Antibiotics and Secondary Metabolite Analysis SHell. Results: Isolates Rc5 and Ru87 showed the highest inhibition activity against selected Gram-positive and Gramnegative pathogens. Neighbor-joining phylogenetic analysis confirmed that isolate Rc5 belonged to Micromonospora oryzae and Micromonospora harpali with 73% bootstrap value while isolate Ru87 was grouped with Streptomyces gingianensis and Streptomyces morales with 89% bootstrap value. Bioinformatics analysis using antiSMASH 3.0 predicted 33 and 19 secondary metabolite gene clusters in Micromonospora sp. Rc5 and Streptomyces sp. Ru87, respectively. Gene annotation predicted the presence of valuable biosynthetic gene clusters in both strains such as polyketides, non-ribosomal peptides, terpenes, siderophores, bacteriocin, lasso peptide, ectoine, and lantipeptide. Conclusion: We concluded that exploring cryptic and novel biosynthetic gene clusters via Illumina whole genome sequencing and bioinformatics analysis is a useful method. We confirmed that Egyptian soil is very rich in high potential biosynthetic of rare actinobacteria. Further genetic engineering manipulation of biosynthetic pathways would eventually lead to producing novel bioactive molecules.