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Grapevine trunk diseases (GTDs) are among the most destructive diseases of vineyards worldwide, including Algeria. In the fungal complex involved in GTD symptoms, referred as grapevine trunk-pathogens, Paeomoniella chlamydospora and Phaeoacremonium minimum have a determining infecting role as pioneer fungi. Due to the lack of efficiency of conventional disease management practices, a search for alternative strategies, such as biocontrol, is needed. Taking the approach of looking for biocontrol candidates in the environment surrounding the plant, the present study explored actinobacteria diversity within vineyard soils of six grape-producing regions in Algeria. Based on their 16S rRNA gene sequence, identification and phylogenic analysis were performed on the 40 isolates of actinobacteria obtained. Forty percent of strains were attached to Streptomyces, including two evidenced new species, and 32.5% were affiliated to Saccharothrix. The other less represented genera were Actinoplanes, Nocardia, Nocardiopsis, Lentzea, Nonomuraea, Promicromonospora, Saccharopolyspora and Streptosporangium. Screening based on antagonistic and plant growth promotion (PGP) abilities of the strains showed that 47.5% of the isolates exhibited appreciable antagonistic activities against both Pa. chlamydospora and Pm. minimum, with the two best strains being Streptomyces sp. Ms18 and Streptomyces sp. Sb11. Screening for plant growth promoting properties demonstrated that majority of the strains were able to produce indole acetic acid, siderophores, ammonia, ACC deaminase, cellulase and amylase, and fix N2. Through a PGP-traits-based cluster analysis, the most interesting strains were highlighted. Taking into account both antagonistic and PGP properties, Streptomyces sp Sb11 was selected as the most promising candidate for further evaluations of its efficiency in a GTDs context.

The biodiversity of actinobacteria in the Mediterranean Sea habitat has drawn limited attention compared to that paid to terrestrial habitats. The work presented here focused on the biodiversity of culturable marine actinobacteria from sediments and seawater collected from the Algerian coast, and led to the identification of 114 actinobacterial isolates. The morphological study revealed higher actinobacterial diversity in sediment than in seawater. Fifty strains were selected for 16 S rRNAgene sequencing. The results revealed that the isolates belonged to ten different genera, Streptomyces (n = 17) and Micromonospora (n = 15) being the most dominant. The remaining actinobacterial isolates, identified as belonging to rare genera, included Nocardia (n = 5), Nocardiopsis (n = 3), Saccharothrix (n = 2), Rhodococcus (n = 2), Promicromonospora (n = 2), Nonomuraea (n = 2), Actinomadura (n = 1) and Saccharomonospora (n = 1). Interestingly, through 16 S rRNA sequence-based identification and phylogenetic analysis, two strains of the genus Streptomyces (MAT1 and MAS22) and a strain of the genus Nonomuraea (MAG8) both constituted a novel species. Screening of antibacterial activity of identified isolates against a panel of human pathogenic bacteria demonstrated that 36% of the isolates were active, particularly against Gram-positive bacteria. The ability to grow in the presence of NaCl and seawater revealed that 98% of the strains were halotolerant, with different levels of NaCl acceptance (from 3 to 13%) but no isolates required seawater to grow.

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.

A novel halophilic actinobacterium strain, designated H8 T , was isolated from a Saharan soil sample collected in El-Goléa, South Algeria. Strain H8 T was identified as representing a new genus using a polyphasic taxonomic approach. Phylogenetic analysis revealed that strain H8 T shared the highest degree of 16S rRNA gene sequence similarity with ‘ Mzabimyces algeriensis ’ DSM 46680 T (93.0 %), Saccharopolyspora ghardaiensis DSM 45606 T (91.2 %), Halopolyspora alba DSM 45976 T (90.8 %) and Actinopolyspora mortivallis DSM 44261 T (90.0 %). The strain was found to grow optimally at 28–35 °C, at pH 6.0–7.0, and in the presence of 15–25 % (w/v) NaCl. The substrate mycelium was observed to be well developed and fragmented in liquid medium and on solid medium. The aerial mycelium was observed to be moderately abundant and to form long chains with non-motile, smooth-surfaced and ovoid or spherical spores at maturity. The cell wall of strain H8 T was found to contain meso -diaminopimelic acid. The whole-cell hydrolysates were found to mainly contain arabinose and galactose. The diagnostic phospholipid detected was phosphatidylcholine, and MK-9(H 4 ), MK-9(H 2 ) and MK-10(H 2 ) were found to be the predominant menaquinones. The major cellular fatty acids were determined to be anteiso-C 17:0 and iso-C 15:0 . The genomic DNA G+C content of strain H8 T was determined to be 71.3 mol%. The genotypic and phenotypic data showed that the strain represents a novel genus and species, for which the name Bounagaea algeriensis gen. nov., sp. nov. is proposed, with the type strain H8 T (=DSM 45966 T  = CECT 8470 T ).

A novel actinomycete strain, designated PAL84, was isolated from a Saharan soil sample collected from Béni-Isguen, Ghardaïa (South of Algeria). This strain was studied for its taxonomic position using a polyphasic approach and was identified as a member of the genus Actinokineospora. Phylogenetic analysis showed that strain PAL84 had 16S rRNA gene sequence similarities with members of the genus Actinokineospora ranging from 96.2 % (Actinokineospora inagensis DSM 44258ᵀ) to 97.8 % (Actinokineospora baliensis NBRC 104211ᵀ). The strain was observed to produce pinkish-purple aerial mycelium and purplish red substrate mycelium, which fragmented readily into chains of non-motile elements. The optimum growth temperature and pH were found to be 25–30 °C and 5.0–7.0, respectively. The cell-wall hydrolysate of strain PAL84 was found to contain meso-diaminopimelic acid and the diagnostic whole-cell sugars were identified as arabinose and galactose. The predominant menaquinone was identified as MK-9 (H₄). The major fatty acids were found to be iso-C₁₆:₀, iso-C₁₅:₀, iso-C₁₆:₁H and iso-C₁₆:₀2OH. The diagnostic phospholipid detected was phosphatidylethanolamine. The genotypic and phenotypic data show that the strain represents a novel species of the genus Actinokineospora, for which the name Actinokineospora mzabensis sp. nov. is proposed, with the type strain PAL84ᵀ(=DSM 45961ᵀ = CECT 8578ᵀ).

A filamentous actinobacterium, designated strain PM3 T , was isolated from a Saharan soil sample collected from Béni-Abbès, Béchar (South-West Algeria). A polyphasic taxonomic study was carried out to establish the status of strain PM3 T . The isolate was found to have morphological and chemotaxonomical properties associated with members of the genus Planomonospora . The new isolated microorganism developed cylindrical sporangia arranged in double parallel rows on aerial mycelium, each one containing a motile single sporangiospore. The cell wall of the strain was found to contain meso -diaminopimelic acid. Whole-cell hydrolysates were found to contain madurose, glucose, mannose and ribose. The predominant menaquinone was identified as MK-9(H 2 ) (69.6%). The polar lipids detected were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylethanolamine, phosphatidylhydroxyethanolamine and glucosamine-containing lipids. The major fatty acids were found to be C 17:1 ω9c (38.6%) and C 17:0 (24.2%). Results of 16S rRNA gene sequence comparison revealed that strain PM3 T shared a high degree of 16S rRNA gene sequence similarity with Planomonospora sphaerica DSM 44632 T (99.3%), Planomonospora parontospora subsp. parontospora DSM 43177 T (99.2%) and P. parontospora subsp. antibiotica DSM 43869 T (99.0%). DNA–DNA hybridization values between strain PM3 T and the type strains of the closely related species were between 58.4 and 70.1%. The combination of phylogenetic analysis, DNA–DNA relatedness data, phenotypic characteristics and chemotaxonomic data support the conclusion that strain PM3 T represents a novel species of the genus Planomonospora , for which the name Planomonospora algeriensis sp. nov. is proposed. The type strain is PM3 T (=DSM 46752 T  = CECT 9047 T ).

A novel thermophilic filamentous bacterium, designated strain T36ᵀ, was isolated from soil sediment sample from a hot spring source collected in Khenchela province, Algeria. Strain T36ᵀ was identified as a member of the genus Thermoactinomyces by a polyphasic approach. Strain T36ᵀ was observed to form white aerial mycelium and non-coloured to pale yellow substrate mycelium, both producing endospores, sessile or borne by short sporophores. The optimum growth temperature and pH were found to be 37–55 °C and 7.0–9.0, respectively and the optimum NaCl concentration for growth was found to be 0–7 % (w/v). The diagnostic diamino acid in the cell wall peptidoglycan was identified as meso-diaminopimelic acid. The predominant menaquinone of strain T36ᵀ was identified as MK-7 (H₀). The major fatty acids were found to be iso-C₁₅:₀ and iso-C₁₇:₀. The phospholipids detected were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and phosphoglycolipid. The chemotaxonomic properties of strain T36ᵀ are consistent with those shared by members of the genus Thermoactinomyces. 16S rRNA gene sequence analysis indicated that the sequence similarities between strain T36ᵀ and Thermoactinomyces species with validly published names were less than 98 %. Based on the combined genotypic and phenotypic evidence, it is proposed that strain T36ᵀ should be classified as representative of a novel species, for which the name Thermoactinomyces khenchelensis sp. nov. is proposed. The type strain is T36ᵀ (=DSM 45951ᵀ = CECT 8579ᵀ).

A novel actinomycete strain, designated PAL84, was isolated from a Saharan soil sample collected from Béni-Isguen, Ghardaïa (South of Algeria). This strain was studied for its taxonomic position using a polyphasic approach and was identified as a member of the genus Actinokineospora . Phylogenetic analysis showed that strain PAL84 had 16S rRNA gene sequence similarities with members of the genus Actinokineospora ranging from 96.2 % ( Actinokineospora inagensis DSM 44258 T ) to 97.8 % ( Actinokineospora baliensis NBRC 104211 T ). The strain was observed to produce pinkish-purple aerial mycelium and purplish red substrate mycelium, which fragmented readily into chains of non-motile elements. The optimum growth temperature and pH were found to be 25–30 °C and 5.0–7.0, respectively. The cell-wall hydrolysate of strain PAL84 was found to contain meso -diaminopimelic acid and the diagnostic whole-cell sugars were identified as arabinose and galactose. The predominant menaquinone was identified as MK-9 (H 4 ). The major fatty acids were found to be iso-C 16:0 , iso-C 15:0 , iso-C 16:1 H and iso-C 16:0 2OH. The diagnostic phospholipid detected was phosphatidylethanolamine. The genotypic and phenotypic data show that the strain represents a novel species of the genus Actinokineospora , for which the name Actinokineospora mzabensis sp. nov. is proposed, with the type strain PAL84 T (=DSM 45961 T  = CECT 8578 T ).

With the aim of studying the biodiversity and the antimicrobial potential of three rare actinobacterial genera: Planomonospora, Saccharothrix and Actinophytocola in Algerian Saharan soils, 65 isolates representing the morphological characteristics of Planomonospora (17) and Saccharothrix/Actinophytocola (48) were isolated from 13 soil samples at 4 different sites in southern Algeria. The isolation was carried out on humic acid-vitamin agar medium using dilution techniques with several soil pretreatment and antibiotics as selective agents. Based on preliminary examination, 21 out of 65 isolates were kept for further investigations: Planomonospora (10) and Saccharothrix/Actinophytocola (11). 16S rRNA gene sequence analysis and DNA/DNA hybridization (DDH) showed that four strains, isolated from two different sites: Béchar (PM3) and Ghardaïa (MB20 and MB27), were found to represent four novel species. Moreover, they formed a distinct phyletic line within the clade of the most related genus: PM3 (DSM 46752T) with Planomonospora, MB27 (DSM 46885T) and MB46 (DSM 46886T) with Saccharothrix and MB20 (DSM 46746T) with Actinophytocola. While many novel species belonging to the genera Saccharothrix have been isolated from Algerian Saharan soils, this is the first report to describe the isolation of new species of Planomonospora and Actinophytocola from this extreme habitat. An assessment of the antimicrobial properties of the actinobacterial strains showed that 38 out of 65 have moderate to strong antimicrobial activities against Gram positive bacteria, fungi or yeasts. These results indicated the importance of further exploration of rare Saharan Actinobacteria for potentially original antimicrobial agents.