Actinoalloteichus hoggarensis sp. nov., an actinomycete isolated from Saharan soil

Antibacterial and antibiofilm properties of two cyclic dipeptides produced by a new desert Streptomyces sp. HG-17 strain against multidrug-resistant pathogenic bacteria

INTRODUCTION

The emergence of multidrug-resistant bacteria and biofilms requires discovering new antimicrobial agents from unexplored environments.

OBJECTIVES

This study aims to isolate and characterize a new actinobacterial strain from the Hoggar Mountains in southern Algeria and evaluate its ability to produce bioactive molecules with potential antibacterial and antibiofilm activities.

METHODS

A novel halotolerant actinobacterial strain, designated HG-17, was isolated from the Hoggar Mountains, and identified based on phenotypic characterizations, 16S rDNA sequence analysis, and phylogenetic analysis. The antibacterial and antibiofilm activities of the strain were assessed, and the presence of biosynthetic genes (PKS-I and NRPS) was confirmed. Two active compounds, HG-7 and HG-9, were extracted butanol solvent, purified by HPLC, and their chemical structures were elucidated using ESI mass spectrometry and NMR spectroscopy.

RESULTS

The strain HG-17 was identified as Streptomyces purpureus NBRC with 98.8% similarity. It exhibited strong activity against multidrug-resistant and biofilm-forming bacteria. The two purified active compounds, HG-7 and HG-9, were identified as cyclo-(d-cis-hydroxyproline-l-phenylalanine) and cyclo-(l-prolone-l-tyrosine), respectively. The minimum inhibitory concentrations (MICs) of HG-7 and HG-9 ranged from 3 to 15 μg/mL, comparable to the MICs of tetracycline (8 to 15 μg/mL). Their minimum biofilm inhibitory concentration (MBIC 50%) showed good inhibition from 48.0 to 52.0% at concentrations of 1 to 7 μg/mL against the tested bacteria.

CONCLUSION

This is the first report of cyclo-(d-cis-hydroxyproline-l-phenylalanine) and cyclo-(l-prolone-l-tyrosine) antibiotics from S. purpureus and their anti-multi-drug-resistant and biofilm-forming bacteria. These results indicate that both antibiotics could be used as effective therapeutics to control infections associated with multidrug-resistant bacteria.

Microbiota and Resistome Analysis of Colostrum and Milk from Dairy Cows Treated with and without Dry Cow Therapies

This study investigated the longitudinal impact of methods for the drying off of cows with and without dry cow therapy (DCT) on the microbiota and resistome profile in colostrum and milk samples from cows. Three groups of healthy dairy cows (n = 24) with different antibiotic treatments during DCT were studied. Colostrum and milk samples from Month 0 (M0), 2 (M2), 4 (M4) and 6 (M6) were analysed using whole-genome shotgun-sequencing. The microbial diversity from antibiotic-treated groups was different and higher than that of the non-antibiotic group. This difference was more evident in milk compared to colostrum, with increasing diversity seen only in antibiotic-treated groups. The microbiome of antibiotic-treated groups clustered separately from the non-antibiotic group at M2-, M4- and M6 milk samples, showing the effect of antibiotic treatment on between-group (beta) diversity. The non-antibiotic group did not show a high relative abundance of mastitis-causing pathogens during early lactation and was more associated with genera such as Psychrobacter, Serratia, Gordonibacter and Brevibacterium. A high relative abundance of antibiotic resistance genes (ARGs) was observed in the milk of antibiotic-treated groups with the Cephaguard group showing a significantly high abundance of genes conferring resistance to cephalosporin, aminoglycoside and penam classes. The data support the use of non-antibiotic alternatives for drying off in cows.

Cytotoxic and antimicrobial activities of secondary metabolites isolated from the deep-sea-derived Actinoalloteichus cyanogriseus 12A22

A new deep-sea-derived actinomycete 12A22 was isolated from the sediment of the South China Sea which showed potential cytotoxic and antimicrobial activities. The actinomycete was identified as Actinoalloteichus cyanogriseus by investigating morphological characteristics and phylogenetic analyses based on its 16S rRNA gene sequence. Two compounds, cyclo-(L-Pro-D-Pro-L-Tyr-L-Tyr) (1) and 2-hydroxyethyl-3-methyl-1,4-naphthoquinone (2), were isolated and characterized from the fermentation broth of the strain 12A22. Compound 2 exhibited significant inhibitory activities against a variety of phytopathogenic fungi (Fusarium oxysporum f. sp. cucumerinum, Setosphaeria turcica, and Botrytis cinerea) and Gram-positive bacterium (Bacillus subtilis). In particular, this compound showed better antifungal activity against Botrytis cinerea than positive control amphotericin B. Besides, compound 2 showed moderate cytotoxic activity against human breast cancer MDA-MB-435 cells with IC50 10.59 µM, weaker than the positive control diaminedichloroplatinum with 5.91 μM. Our results suggested that this naphthoquinone could be used as a potential antimicrobial and antitumor agent.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02846-0.

Bioactive Alkaloids from the Actinomycete Actinoalloteichus sp. ZZ1866

The new alkaloids marinacarbolines E-Q (1-10, 12-14), caerulomycin N (15), and actinoallonaphthyridine A (16), together with the known marinacarboline C (11) and cyanogramide (17), were isolated from the actinomycete Actinoalloteichus sp. ZZ1866. The structures of the isolated compounds were elucidated based on their HRESIMS data, extensive NMR spectroscopic analyses, Mosher's method, ECD calculations, single-crystal X-ray diffraction analysis, and chemical degradation studies. Marinacarbolines E-L (1-8) share an indole-pyridone-imidazole tetracyclic skeleton, which is the first example of this kind of skeleton. Caerulomycin N (15) and cyanogramide (17) exhibited cytotoxic activity against both human glioma U251 and U87MG cells with IC₅₀ values of 2.0-7.2 μM. Marinacarbolines E (1), G (3), I (5), and M (9) showed cytotoxic activity against U87MG cells with IC₅₀ values of 2.3-8.9 μM.

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.

Actinoalloteichus fjordicus sp. nov. isolated from marine sponges: phenotypic, chemotaxonomic and genomic characterisation

Two actinobacterial strains, ADI 127-17^T and GBA 129-24, isolated from marine sponges Antho dichotoma and Geodia barretti, respectively, collected at the Trondheim fjord in Norway, were the subjects of a polyphasic study. According to their 16S rRNA gene sequences, the new isolates were preliminarily classified as belonging to the genus Actinoalloteichus. Both strains formed a distinct branch, closely related to the type strains of Actinoalloteichus hoggarensis and Actinoalloteichus hymeniacidonis, within the evolutionary radiation of the genus Actinoalloteichus in the 16S rRNA gene-based phylogenetic tree. Isolates ADI 127-17^T and GBA 129-24 exhibited morphological, chemotaxonomic and genotypic features distinguishable from their close phylogenetic neighbours. Digital DNA: DNA hybridization and ANI values between strains ADI 127-17^T and GBA 129-24 were 97.6 and 99.7%, respectively, whereas the corresponding values between both tested strains and type strains of their closely related phylogenetic neighbours, A. hoggarensis and A. hymeniacidonis, were well below the threshold for delineation of prokaryotic species. Therefore, strains ADI 127-17^T (= DSM 46855^T) and GBA 129-24 (= DSM 46856) are concluded to represent a novel species of the genus Actinoalloteichus for which the name of Actinoalloteichus fjordicus sp. nov. (type strain ADI 127-17^T = DSM 46855^T = CECT 9355^T) is proposed. The complete genome sequences of the new strains were obtained and compared to that of A. hymeniacidonis DSM 45092^T and A. hoggarensis DSM 45943^T to unravel unique genome features and biosynthetic potential of the new isolates.

Complete genome sequence of the actinomycete Actinoalloteichus hymeniacidonis type strain HPA 177T isolated from a marine sponge

Actinoalloteichus hymeniacidonis HPA 177T is a Gram-positive, strictly aerobic, black pigment producing and spore-forming actinomycete, which forms branching vegetative hyphae and was isolated from the marine sponge Hymeniacidon perlevis. Actinomycete bacteria are prolific producers of secondary metabolites, some of which have been developed into anti-microbial, anti-tumor and immunosuppressive drugs currently used in human therapy. Considering this and the growing interest in natural products as sources of new drugs, actinomycete bacteria from the hitherto poorly explored marine environments may represent promising sources for drug discovery. As A. hymeniacidonis, isolated from the marine sponge, is a type strain of the recently described and rare genus Actinoalloteichus, knowledge of the complete genome sequence enables genome analyses to identify genetic loci for novel bioactive compounds. This project, describing the 6.31 Mbp long chromosome, with its 5346 protein-coding and 73 RNA genes, will aid the Genomic Encyclopedia of Bacteria and Archaea project.

Actinomadura algeriensis sp. nov., an actinobacterium isolated from Saharan soil

During the course of a screening programme for new taxa of actinobacteria, a strain designated ACD1(T), was isolated from a Saharan soil in the Hoggar region (Algeria). The taxonomic position of this strain was determined using a polyphasic taxonomic approach. The strain was observed to form extensively branched, non-fragmenting substrate mycelium, and aerial mycelium with straight to flexuous, hooked and irregular spirals (1-2 turns) forming short chains of spores. The diamino acid present in the cell wall is meso-diaminopimelic acid. Galactose, glucose, madurose, mannose and ribose occur in whole-cell hydrolysates. The diagnostic phospholipids detected were diphosphatidylglycerol and phosphatidylinositol. The major menaquinones were identified as MK-9 (H4) and MK-9 (H2). The major fatty acids were found to be C16:0, C18:1 cis9, iso-C16:0 and 10-methyl C18:0. Phylogenetic analysis based on the 16S rRNA gene showed that the strain belongs to the genus Actinomadura, and is closely related to Actinomadura sediminis DSM 45500(T) (98.5 % similarity) and Actinomadura cremea subsp. cremea DSM 43676(T) (98.3 % similarity). However, DNA-DNA hybridization revealed only 48.0 % relatedness with A. sediminis DSM 45500(T) and 33.2 % relatedness with A. cremea subsp. cremea DSM 43676(T). The combined phenotypic and genotypic data showed that the strain represents a novel species of the genus Actinomadura, for which the name Actinomadura algeriensis sp. nov. is proposed, with the type strain ACD1(T) (= DSM 46744(T) = CECT 8841(T)).