Atika Meklat

Isolation, Taxonomy, and Antagonistic Properties of Halophilic Actinomycetes in Saharan Soils of Algeria

ABSTRACT The diversity of a population of 52 halophilic actinomycetes was evaluated by a polyphasic approach, which showed the presence of members of the Actinopolyspora, Nocardiopsis, Saccharomonospora, Streptomonospora, and Saccharopolyspora genera. One strain was considered to be a new member of the last genus, and several other strains seemed to be new species. Furthermore, 50% of strains were active against a broad range of indicators and contained genes encoding polyketide synthetases and nonribosomal peptide synthetases.

Saccharothrix sp. PAL54, a new chloramphenicol-producing strain isolated from a Saharan soil

An actinomycete strain designated PAL54, producing an antibacterial substance, was isolated from a Saharan soil in Ghardaïa, Algeria. Morphological and chemical studies indicated that this strain belonged to the genus Saccharothrix. Analysis of the 16S rDNA sequence showed a similarity level ranging between 96.9 and 99.2% within Saccharothrix species, with S. longispora DSM 43749T, the most closely related. DNA–DNA hybridization confirmed that strain PAL54 belonged to Saccharothrix longispora. It showed very strong activity against pathogenic Gram-positive and Gram-negative bacteria responsible for nosocomial infections and resistant to multiple antibiotics. Strain PAL54 secreted the antibiotic optimally during mid-stationary and decline phases of growth. One antibacterial compound was isolated from the culture broth and purified by HPLC. The active compound was elucidated by uv-visible and NMR spectroscopy and by mass spectrometry. The results showed that this compound was a d(−)-threo chloramphenicol. This is the first report of chloramphenicol production by a Saccharothrix species.

Actinopolyspora mzabensis sp. nov., a halophilic actinomycete isolated from an Algerian Saharan soil.

A halophilic actinomycete strain, designated H55(T), was isolated from Saharan soil sampled in the Mzab region (Ghardaïa, southern Algeria) and was characterized in a taxonomic study using a polyphasic approach. The cell wall was determined to contain meso-diaminopimelic acid and the characteristic whole-cell sugars were arabinose and galactose. The predominant menaquinones were found to be MK-10(H4) and MK-9(H4). The predominant cellular fatty acids were determined to be anteiso-C17 : 0, iso-C16 : 0 and iso-C15 : 0. The diagnostic phospholipid detected was phosphatidylcholine. The morphological and chemotaxonomic characteristics of the strain were consistent with those of members of the genus Actinopolyspora, and 16S rRNA gene sequence analysis confirmed that strain H55(T) was a member of this genus. DNA-DNA hybridization values between strain H55(T) and the type strains of the nearest species of the genus Actinopolyspora, Actinopolyspora erythraea and A. alba, were clearly below the 70 % threshold. The genotypic and phenotypic data showed that the organism represents a novel species of the genus Actinopolyspora, for which the name Actinopolyspora mzabensis sp. nov. is proposed, with the type strain H55(T) ( = DSM 45460(T) = CCUG 62965(T)).

Saccharopolyspora ghardaiensis sp. nov., an extremely halophilic actinomycete isolated from Algerian Saharan soil

A novel halophilic actinomycete, strain designated H53T, was isolated from a Saharan soil sample collected from Chaâbet Ntissa, Béni-isguen, Ghardaïa (South of Algeria) and was characterized taxonomically by means of polyphasic approach. Optimal growth was found to occur at 30–35 °C, pH 6–7 and in the presence of 15–25% (w/v) NaCl. The strain was observed to produce abundant aerial mycelium, which formed long chains of rod-shaped spores at maturity, and well developed and fragmented substrate mycelium. The cell wall was determined to contain meso-diaminopimelic acid; the diagnostic whole-cell sugars were arabinose and galactose. The predominant menaquinones were found to be MK-9(H4) and MK-9(H6). The predominant cellular fatty acids were determined to be iso- and anteiso-C17:0, iso-C15:0, and cis9 iso-C17:1. The diagnostic phospholipid detected was phosphatidylcholine. The morphological and chemotaxonomic characteristics of the strain were consistent with those of members of the genus Saccharopolyspora. Phylogenetic analyses on the basis of the 16S ribosomal RNA (rRNA) gene sequence showed that this strain formed a distinct phyletic line within the radiation of the genus Saccharopolyspora. The 16S rRNA sequence similarities between strain H53T and other members of the genus Saccharopolyspora ranged from 92.1 to 94.3%. The DNA G+C content of strain H53T was 72.6%. The genotypic and phenotypic data showed that the strain H53T represents a novel species of the genus Saccharopolyspora, for which the name Saccharopolyspora ghardaiensis sp. nov. is proposed, with the type strain H53T (=DSM 45606T=CCUG 63370T=CECT 8304T).

A novel hydroxamic acid-containing antibiotic produced by a Saharan soil-living Streptomyces strain.

During screening for potentially antimicrobial actinobacteria, a highly antagonistic strain, designated WAB9, was isolated from a Saharan soil of Algeria. A polyphasic approach characterized the strain taxonomically as a member of the genus Streptomyces. The strain WAB9 exhibited a broad spectrum of antimicrobial activity toward various multidrug‐resistant micro‐organisms. A PCR‐based assay of genomic potential for producing bioactive metabolites revealed the presence of PKS‐II gene. After 6 days of strain fermentation, one bioactive compound was extracted from the remaining aqueous phase and then purified by HPLC. The chemical structure of the compound was determined by spectroscopic (UV–visible, and 1H and 13C NMR) and spectrometric analysis. The compound was identified to be 2‐amino‐N‐(2‐amino‐3‐phenylpropanoyl)‐N‐hydroxy‐3‐phenylpropanamide, a novel hydroxamic acid‐containing molecule. The pure molecule showed appreciable minimum inhibitory concentration values against a selection of drug‐resistant bacteria, filamentous fungi and yeasts.

Prauserella isguenensis sp. nov., a halophilic actinomycete isolated from desert soil

Two actinomycete strains, designated H225(T) and H137, were isolated from two soil samples collected from the arid region of Ahbas at Béni-Isguen (Mzab), located in the Algerian Sahara. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the novel strains should be assigned to the genus Prauserella of the family Pseudonocardiaceae , and they were therefore subjected to a polyphasic taxonomic study. These two strains contained meso-diaminopimelic acid as the diagnostic diamino acid and arabinose and galactose as major whole-cell sugars. The diagnostic phospholipid was phosphatidylethanolamine. The predominant menaquinone was MK-9(H4), and the major fatty acid was iso-C16 : 0. DNA-DNA hybridization values between strain H225(T) and its closest phylogenetic neighbours, namely Prauserella flava DSM 45265(T), Prauserella alba DSM 44590(T), Prauserella aidingensis DSM 45266(T), Prauserella salsuginis DSM 45264(T) and Prauserella sediminis DSM 45267(T), were clearly below the 70% threshold used for species delineation. The genomic DNA G+C content of strains H225(T) and H137 was 70.4 mol%. On the basis of phenotypic and genotypic data, strains H225(T) and H137(T) are considered to represent a novel species of the genus Prauserella , for which the name Prauserella isguenensis sp. nov. is proposed. The type strain is H225(T) ( =DSM 46664(T) = CECT 8577(T)).

A novel strain of Actinopolyspora mortivallis with antibacterial activity isolated from a Saharan soil

A new halophilic actinomycete strain, designated H16, has been isolated from a hypersaline Saharan soil in Ouargla province (southern Algeria) and characterized taxonomically using a polyphasic approach. The strain grew at 18–50°C, pH 5–9, and 7–32% (w/v) NaCl. It produced abundant aerial mycelia, which formed long chains of rod-shaped spores at maturity, and fragmented substrate mycelia. The strain contained chemotaxonomic markers that were diagnostic for the genus Actinopolyspora, such as meso-diaminopimelic acid, arabinose, and galactose, phosphatidylcholine as a diagnostic phospholipid, and predominant menaquinones MK-9(H4) and MK-10(H4). The predominant fatty acids were anteiso- and iso-C17:0, iso-C15:0, and 9-methyl-C16:0. Phylogenetic analysis, based on 16S rDNA gene sequences, confirmed that strain H16 is a member of the genus Actinopolyspora and most closely related to A. mortivallis (98.7% identity). DNA–DNA hybridization confirmed that it belonged to A. mortivallis. This strain showed high activity against Klebsiella pneumoniae and optimally secreted antibiotics during the mid-stationary growth phase in liquid culture. The antibiotics were extracted with n-butanol and separated on silica gel plates by ethanol–ammonia–water (mobile phase). The results of bioautography revealed the presence of five antibiotics. The chemical revelations showed that these antibiotics were glycosylated polycyclic aromatic compounds containing amine groups and hydroxamic acids. The UV-visible and mass spectra of the most active antibiotics were determined.

Diversity and antagonistic properties of culturable halophilic actinobacteria in soils of two arid regions of septentrional Sahara:M'zab and Zibans

The diversity of culturable halophilic actinobacteria in two Algerian arid ecosystems (M’zab and Zibans) of septentrional Sahara was investigated. A total of 69 halophilic strains were isolated from 19 soil samples. Taxonomy was determined using a polyphasic approach based on morphological, physiological (with the application of numerical taxonomy), chemotaxonomic and molecular investigations. Sequencing of the 16S rRNA gene revealed that the strains belonged to six clusters corresponding to six genera: Actinopolyspora, Nocardiopsis, Prauserella, Saccharomonospora, Saccharopolyspora and Streptomonospora. Some strains were found to represent known species, but others formed distinct phyletic lines. Interestingly, cluster VII, which contained four strains, represents an unknown actinobacterial genus. An assessment of the biological properties of the actinobacterial strains showed moderate to strong antimicrobial activities against fungi and bacteria, including methicillin-resistant Staphylococcus aureus. The bioactive potential of strains which did not show any antimicrobial activity on yeast extract-malt extract agar was analyzed based on the genetic background of these strains using polyketide synthase (type I, II and PKSE) and non-ribosomal peptide synthetase (NRPS) gene sequences. Most of the strains harbored NRPS and PKS-II genes, indicating that they might have a great potential to produce bioactive compounds if the laboratory culture conditions were changed.