Saccharothrix tamanrassetensis sp. nov., an actinomycete isolated from Saharan soil

Diversity and Bioactivity of Endophytic Actinobacteria Associated with the Roots of Artemisia herba-alba Asso from Algeria

The isolation of endophytic actinobacteria from the roots of wild populations of Artemisia herba-alba Asso, a medicinal plant collected from the arid lands of Algeria, is reported for the first time. Forty-five actinobacterial isolates were identified by molecular analysis and in vitro evaluated for antimicrobial activity and plant growth-promoting (PGP) abilities (1-Aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, nitrogen fixation, phosphate and potassium solubilization, ammonia, and siderophores production). The phylogenetic relationships based on 16S rRNA gene sequences show that the genus Nocardioides (n = 23) was dominant in the sampled localities. The remaining actinobacterial isolates were identified as Promicromonospora (n = 11), Streptomyces (n = 6), Micromonopora (n = 3), and Saccharothrix (n = 2). Only six (13.33%) strains (five Streptomyces and one Saccharothrix species) were antagonistic in vitro against at least one or more indicator microorganisms. The antimicrobial activity of actinobacterial strains targeted mainly Gram-positive bacteria. The results demonstrate that more than 73% of the isolated strains had ACC deaminase activity, could fix atmospheric nitrogen and were producers of ammonia and siderophores. However, only one (2.22%) strain named Saccharothrix sp. BT79 could solubilize phosphorus and potassium. Overall, many strains exhibited a broad spectrum of PGP abilities. Thus, A. herba-alba provides a source of endophytic actinobacteria that should be explored for their potential biological activities.

Actinobacteria From Desert: Diversity and Biotechnological Applications

Deserts, as an unexplored extreme ecosystem, are known to harbor diverse actinobacteria with biotechnological potential. Both multidrug-resistant (MDR) pathogens and environmental issues have sharply raised the emerging demand for functional actinobacteria. From 2000 to 2021, 129 new species have been continuously reported from 35 deserts worldwide. The two largest numbers are of the members of the genera Streptomyces and Geodermatophilus, followed by other functional extremophilic strains such as alkaliphiles, halotolerant species, thermophiles, and psychrotolerant species. Improved isolation strategies for the recovery of culturable and unculturable desert actinobacteria are crucial for the exploration of their diversity and offer a better understanding of their survival mechanisms under extreme environmental stresses. The main bioprospecting processes involve isolation of target actinobacteria on selective media and incubation and selection of representatives from isolation plates for further investigations. Bioactive compounds obtained from desert actinobacteria are being continuously explored for their biotechnological potential, especially in medicine. To date, there are more than 50 novel compounds discovered from these gifted actinobacteria with potential antimicrobial activities, including anti-MDR pathogens and anti-inflammatory, antivirus, antifungal, antiallergic, antibacterial, antitumor, and cytotoxic activities. A range of plant growth-promoting abilities of the desert actinobacteria inspired great interest in their agricultural potential. In addition, several degradative, oxidative, and other functional enzymes from desert strains can be applied in the industry and the environment. This review aims to provide a comprehensive overview of desert environments as a remarkable source of diverse actinobacteria while such rich diversity offers an underexplored resource for biotechnological exploitations.

Diversity of Actinobacteria Isolated from Date Palms Rhizosphere and Saline Environments: Isolation, Identification and Biological Activity Evaluation

The diversity of cultural Actinobacteria in two types of Algerian Sahara environments, including saline environments and date palms rhizosphere, was investigated. In this study, a total of 40 strains of actinomycetes was isolated from different soil samples, using a rehydration and centrifugation method. Molecular identification, based on 16S rRNA gene sequence analysis, revealed that these isolates were affiliated to six clusters corresponding to eight genera, including Streptomyces, Nocardiopsis, Saccharopolyspora, Actinomadura, Actinocorallia, Micromonospora, Couchioplanes, and Planomonospora. A taxonomic analysis, based on the morphological, physiological, biochemical, and molecular investigation, of selected strains, which belong to the rare Actinobacteria, was undertaken. Four strains (CG3, A111, A93, and A79) were found to form distinct phyletic lines and represent new actinobacterial taxa. An assessment of antimicrobial proprieties of the 40 obtained actinomycetes strains, showed moderate to strong antimicrobial activities against fungi and bacteria. This study demonstrated the richness of Algerian Sahara with rare Actinobacteria, which can provide novel bioactive metabolites, to solving some of the most challenging problems of the day, such as multi-drug resistance.

Saccharothrix deserti sp. nov., an actinomycete isolated from desert soil

A Gram-stain-positive, aerobic actinomycete, designated strain BMP B8144^T, was isolated from desert soil, in Xinjiang province, northwest China. The isolate produced scanty aerial mycelium and fragmented substrate mycelium on most tested media. Cell-wall hydrolysates contained meso-diaminopimelic acid, galactose and mannose. The diagnostic phospholipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylhydroxylethanolamine, phosphatidylinositol, and phosphatidylinositol mannosides. The major fatty acids included iso-C_16 : 0, C_17 : 1 ω8c and iso-C_15 : 0. The predominant menaquinones were MK-9(H₄) and MK-10(H₄). The DNA G+C content was 70.4 mol% (genome). Based on the 16S rRNA gene sequence analysis on EzBioCloud server, strain BMP B8144^T showed the closest similarities to Saccharothrix lopnurensis YIM LPA2h^T (98.9 %) and 'Saccharothrix yanglingensis' Hhs.015 (98.6 %). However, it can be distinguished from the closest strains based on the low levels of DNA-DNA relatedness (59.3±1.8 and 47.9±2.3 %, respectively). A combination of morphological, chemotaxonomic and phylogenetic characteristics, strain BMP B8144^T represents a novel species of the genus Saccharothrix, for which the name Saccharothrix deserti sp. nov. is proposed. The type strain is BMP B8144^T (=CGMCC 4.7490^T=KCTC 49001^T).

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.

Antimicrobial activities of novel bipyridine compounds produced by a new strain of Saccharothrix isolated from Saharan soil

The actinobacterium strain ABH26 closely related to Saccharothrix xinjiangensis, isolated from an Algerian Saharan soil sample, exhibited highly antagonist activity against Gram-positive bacteria, yeasts and filamentous fungi. Its ability to produce antimicrobial compounds was investigated using several solid culture media. The highest antimicrobial activity was obtained on Bennett medium. The antibiotics secreted by strain ABH26 on Bennett medium were extracted by methanol and purified by reverse-phase HPLC using a C18 column. The chemical structures of the compounds were determined after spectroscopic (¹H NMR, ¹³C NMR, ¹H-¹H COSY and ¹H-¹³C HMBC spectra), and spectrometric (mass spectrum) analyses. Two new cyanogriside antibiotics named cyanogriside I (1) and cyanogriside J (2), were characterized along with three known caerulomycins, caerulomycin A (3), caerulomycin F (4) and caerulomycinonitrile (5). This is the first report of cyanogrisides and caerulomycins production by a member of the Saccharothrix genus. The minimum inhibitory concentrations (MIC) of these antibiotics were determined against pathogenic microorganisms.

Saccharothrix ghardaiensis sp. nov., an actinobacterium isolated from Saharan soil

The taxonomic position of a new Saccharothrix strain, designated MB46^T, isolated from a Saharan soil sample collected in Mzab region (Ghardaïa province, South Algeria) was established following a polyphasic approach. The novel microorganism has morphological and chemical characteristics typical of the members of the genus Saccharothrix and formed a phyletic line at the periphery of the Saccharothrix espanaensis subcluster in the 16S rRNA gene dendrograms. Results of the 16S rRNA gene sequence comparisons revealed that strain MB46^T shares high degrees of similarity with S. espanaensis DSM 44229^T (99.2%), Saccharothrix variisporea DSM 43911^T (98.7%) and Saccharothrix texasensis NRRL B-16134^T (98.6%). However, the new strain exhibited only 12.5-17.5% DNA relatedness to the neighbouring Saccharothrix spp. On the basis of phenotypic characteristics, 16S rRNA gene sequence comparisons and DNA-DNA hybridizations, strain MB46^T is concluded to represent a novel species of the genus Saccharothrix, for which the name Saccharothrix ghardaiensis sp. nov. (type strain MB46^T = DSM 46886^T = CECT 9046^T) is proposed.

Saccharothrix isguenensis sp. nov., an actinobacterium isolated from desert soil

A novel actinobacterial strain, designated MB27T, was isolated from a Saharan soil sample collected in Mzab region (Ghardaïa province, South Algeria). Strain MB27T was characterized following a polyphasic taxonomic approach. This strain produced a branched and fragmented substrate mycelium, which was found to have a yellowish orange colour. A white scanty aerial mycelium was produced on most media tested. Chemotaxonomic and phylogenetic studies clearly demonstrated that strain MB27T belongs to the family Pseudonocardiaceae and is closely related to the genus Saccharothrix. Cell-wall hydrolysates contained meso-diaminopimelic acid but not glycine, and whole-cell hydrolysates contained galactose, glucose, ribose and small amounts of mannose and rhamnose. The detected phospholipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannosides. Mycolic acids were not detected while the predominant fatty acid was iso-branched hexadecanoate (iso-C16 : 0). The major menaquinone was MK-9(H4). Results of 16S rRNA gene sequence comparisons revealed that strain MB27T shairs the highest degree of similarity with Saccharothrix ecbatanensis DSM 45486T (99.8%), Saccharothrix hoggarensis DSM 45457T (99.3 %), Saccharothrix longispora DSM 43749T (98.6 %) and Saccharothrix yanglingensis DSM 45665T (98.6 %). However, it exhibited only 11-42 % DNA-DNA relatedness to the neighbouring Saccharothrixspecies. On the basis of phenotypic characteristics, 16S rRNA gene sequence comparisons and DNA-DNA hybridization, strain MB27T is shown to represent a novel species of the genus Saccharothrix, for which the name Saccharothrix isguenensis sp. nov. (type strain MB27T=DSM 46885T=CECT 9045T) is proposed.

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

A novel actinobacterial strain, designated ACD12^T, was isolated from a Saharan soil sample collected from Adrar province, southern Algeria. A polyphasic study was carried out to establish the taxonomic position of this strain. Strain ACD12^T was observed to form extensively branched substrate mycelia. Aerial mycelium was absent or was weakly produced on all media tested, while spore chains were short with a hooked and irregular spiral form (2-3 turns). The dominant diaminopimelic acid isomer in the cell wall was meso-diaminopimelic acid. Glucose, ribose, galactose, mannose and madurose occured in whole-cell hydrolysates. The major phospholipid was diphosphatidylglycerol and phosphatidylinositol. The predominant menaquinone was MK-9(H6). The fatty acid profile was characterized by the presence of C16 : 0, C17 : 0, C15 : 0, C18 : 0, C18 : 1 cis9 and iso-C16 : 0. Results of 16S rRNA gene sequence comparisons revealed that strain ACD12^T shared the highest degree of 16S rRNA gene sequence similarity with Actinomadura sputi DSM 45233^T (98.3 %) and Actinomadura hallensis DSM 45043^T (97.8 %). All tree-making algorithms used also supported strain ACD12^T forming a distinct clade with its most closely related species. In addition, DNA-DNA hybridization indicated only 39.8 % relatedness with A. sputi DSM 45233^T and 18.7 % relatedness with A. hallensis DSM 45043^T. The combined phenotypic and genotypic data show that the novel isolate represents a novel species of the genus Actinomadura, for which the name Actinomadura adrarensis sp. nov., is proposed, with the type strain ACD12^T (=DSM 46745^T =CECT 8842^T).

Saccharothrix stipae sp. nov., an actinomycete isolated from the rhizosphere of Stipa grandis

An actinomycete, strain D34^T, was isolated from a soil sample collected from the rhizosphere of Stipa grandis at Yunwu Mountain in Ningxia, north-west China. Strain D34^T showed highest 16S rRNA gene sequence similarity to Saccharothrix espanaensis DSM 44229^T (99.0 %), Saccharothrix texasensis NRRL B-16107^T (98.7 %) and Saccharothrix variisporea NRRL B-16296^T (98.6 %). The strain contained meso-diaminopimelic acid, alanine, glycine and glutamic acid as major cell-wall amino acids. Mannose, rhamnose and galactose were the characteristic whole-cell sugars. The fatty acid profile consisted predominantly of iso-C_15 : 0, iso-C_16 : 0, iso-C_16 : 1, C_17 : 1ω6c, anteiso-C_17 : 0 and anteiso-C_15 : 0. The phospholipid profile included phosphatidylethanolamine (typical of phospholipid pattern type II). Furthermore, a combination of some physiological and biochemical properties and low DNA-DNA relatedness values indicated that strain D34^T was differentiated from members of closely related species. On the basis of these phenotypic, genotypic and chemotaxonomic data, strain D34^T represents a novel species of the genus Saccharothrix, for which the name Saccharothrix stipae sp. nov. is proposed. The type strain is D34^T ( = JCM 30560^T = ACCC19714^T).

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)).