Abdelghani Zitouni

Biocontrol of Rhizoctonia solani damping-off and promotion of tomato plant growth by endophytic actinomycetes isolated from native plants of Algerian Sahara?

Thirty-four endophytic actinomycetes were isolated from the roots of native plants of the Algerian Sahara. Morphological and chemical studies showed that twenty-nine isolates belonged to the Streptomyces genus and five were non-Streptomyces. All isolates were screened for their in vitro antifungal activity against Rhizoctonia solani. The six that had the greatest pathogen inhibitory capacities were subsequently tested for their in vivo biocontrol potential on R. solani damping-off in sterilized and non-sterilized soils, and for their plant-growth promoting activities on tomato seedlings. In both soils, coating tomato seeds with antagonistic isolates significantly reduced (P<0.05) the severity of damping-off of tomato seedlings. Among the isolates tested, the strains CA-2 and AA-2 exhibited the same disease incidence reduction as thioperoxydicarbonic diamide, tetramethylthiram (TMTD) and no significant differences (P<0.05) were observed. Furthermore, they resulted in a significant increase in the seedling fresh weight, the seedling length and the root length of the seed-treated seedlings compared to the control. The taxonomic position based on 16S rDNA sequence analysis and phylogenetic studies indicated that the strains CA-2 and AA-2 were related to Streptomyces mutabilis NBRC 12800(T) (100% of similarity) and Streptomyces cyaneofuscatus JCM 4364(T) (100% of similarity), respectively.

Taxonomy and chemical characterization of new antibiotics produced by Saccharothrix SA198 isolated from a Saharan soil

Actinomycete strain SA198, isolated from a Saharan soil sample of Algeria, exhibited antimicrobial activity against Gram-positive and Gram-negative bacteria, and phytopathogenic and toxinogenic fungi. The morphological and chemotaxonomic characteristics of the strain were consistent with those of the genus Saccharothrix. Analysis of the 16S rRNA gene sequence of strain SA198 showed a similarity level ranging between 97.2 and 98.8% within Saccharothrix species, S. australiensis being the most closely related. Two new active products were isolated by reverse HPLC using a C18 column. The ultraviolet-visible (UV-VIS), infrared (IR), mass, and (1)H and (14)C nuclear magnetic resonance (NMR) spectra showed that these products were new bioactive compounds. The minimum inhibitory concentrations of these antibiotics showed a strong activity against fungi and moderate activities against Gram-positive and Gram-negative bacteria.

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.

New Dithiolopyrrolone Antibiotics from Saccharothrix sp. SA 233

Three new natural dithiopyrrolone antibiotics, 3-methyl-2-butenoylpyrrothine (1), tigloylpyrrothine (2), and n-butyropyrrothine (3) were isolated along with the known isobutyropyrrothine (4) and thiolutin (5) from the fermentation broth of Saccharothrix sp. SA 233. The structures of the novel compounds were established on the basis on their spectral data.

Essential oils from wild populations of Algerian Lavandula stoechas L.: composition, chemical variability, and in vitro biological properties.

In an effort to develop local productions of aromatic and medicinal plants, a comprehensive assessment of the composition and biological activities of the essential oils (EOs) extracted from the aerial flowering parts of wild growing Lavandula stoechas L. collected from eleven different locations in northern Algeria was performed. The oils were characterized by GC‐FID and GC/MS analyses, and 121 compounds were identified, accounting for 69.88–91.2% of the total oil compositions. The eleven oils greatly differed in their compositions, since only 66 compounds were common to all oils. Major EO components were fenchone (2; 11.27–37.48%), camphor (3, 1.94–21.8%), 1,8‐cineole (1; 0.16–8.71%), and viridiflorol (10; 2.89–7.38%). The assessed in vitro biological properties demonstrated that the DPPH‐based radical‐scavenging activities and the inhibition of the β‐carotene/linoleic acid‐based lipid oxidation differed by an eight‐fold factor between the most and the least active oils and were linked to different sets of molecules in the different EOs. The eleven EOs exhibited good antimicrobial activities against most of the 16 tested strains of bacteria, filamentous fungi, and yeasts, with minimum inhibitory concentrations (MICs) ranging from 0.16 to 11.90 mg/ml.

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.

Characterization and antagonistic properties of Streptomyces strains isolated from Saharan soils, and evaluation of their ability to control seedling blight of barley caused by Fusarium culmorum

During a screening for potential plant disease control actinomycetes, a total of 133 strains were isolated from Saharan soil samples of seven Algerian regions by dilution technique on chitin‐vitamins agar medium. Screening for antagonistic properties using streak assay method showed that 25% of isolates demonstrated strong activities against a wide range of plant pathogenic fungi. Due to their strong anti‐Fusarium activities, six of these isolates were selected and subsequently related to Streptomyces species by polyphasic analysis. These isolates were evaluated for their biocontrol ability against Fusarium culmorum, a serious pathogenic fungus of cereals crops related to damping‐off and seedling blight resulting in yield loss. Barley seeds were chosen as cereal plant model. Surface bacterized seeds with TW3, RI3 and TW2 strains expressed the highest performances and permit to reduce significantly both the disease occurrence on seedlings (62–76%) and the extent of seedling blight symptoms (over than 95%). However, a negative effect on plant establishment was observed for RI3 treatment.

Antifungal properties of an actinomycin D‐producing strain, Streptomyces sp. IA1, isolated from a Saharan soil

An actinomycete strain named IA1, which produced an antimicrobial compound, was isolated from a Saharan soil in In Amenas, Algeria. The study of the 16S rDNA sequence of this strain permitted to relate it to Streptomyces mutabilis NBRC 12800T (99.93% of similarity). Strain IA1 exhibited strong activity against a wide range of plant pathogenic fungi. One bioactive compound produced in large amounts (46.7 mg L−1 day−1), named YA, was isolated and purified by TLC and reverse phase HPLC. The structure elucidation of the pure substance, using combined data from UV visible, NMR spectra, and mass spectrometry, permitted to identify it as actinomycin D, and was thus found for the first time in S. mutabilis related species. The biocontrol abilities of the strain IA1 and compound YA were evaluated through two diseases, i.e., chocolate spot of field bean and Fusarium wilt of flax. The occurrence of the two fungal diseases was effectively reduced. The reduction of chocolate spot disease symptoms reached 80 and 91.7% with IA1 and YA seedlings pretreatments, respectively. Soil pretreatment with IA1 or YA also allowed to reduce Fusarium wilt disease impact by almost 60%.

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

An actinomycete, designated SA181(T), was isolated from Saharan soil in the Hoggar region (south Algeria) and was characterized taxonomically by using a polyphasic approach. The morphological and chemotaxonomic characteristics of the isolate were consistent with the genus Saccharothrix, and 16S rRNA gene sequence analysis confirmed that strain SA181(T) was a novel member of the genus Saccharothrix. DNA-DNA hybridization values between strain SA181(T) and its closest phylogenetic neighbours, the type strains of Saccharothrix longispora, Saccharothrix texasensis and Saccharothrix xinjiangensis, were clearly below the 70 % threshold. The genotypic and phenotypic data showed that the isolate represents a novel species of the genus Saccharothrix, for which the name Saccharothrix hoggarensis sp. nov. is proposed, with the type strain SA181(T) ( = DSM 45457(T)  = CCUG 60214(T)).

Antibiotic R2, a new angucyclinone compound from Streptosporangium sp. Sg3

Angucyclinones are a subclass of angucyclines, which are defined as microbial quinone natural products related to tetracyclines and anthracyclines and bearing, as characteristic structural feature, a tetracyclic benz[a]anthracene ring system assembled in an angular manner.1 This structural moiety is biosynthetically derived from a decaketide chain formed via the polyketide biosynthetic pathway. The term ‘angucycline’ includes molecules with hydrolysable sugar moieties, whereas ‘angucyclinone’ refers to a sugarless compound or a compound with a C-glycosidic linked sugar moiety.1,2 Angucyclines are isolated from the fermentation broth of actinomycetes, mostly from the genus Streptomyces, but also from Actinomadura, Nocardia and Streptosporangium genera.1 Angucyclines show a broad spectrum of biological activities including antitumor,1,2 antibacterial, antifungal, antiviral,3,4 enzyme inhibitory5,6 and platelet aggregation inhibitory properties.7,8 In a continuous search for new bioactive compounds from actinomycetes other than the genus Streptomyces, several Saharan soil samples collected in arid ecosystems were explored.9–11 Among the isolates, we were interested by a new actinomycete strain belonging to the genus Streptosporangium and producing a new compound (R2) identified as a new angucyclinone. This paper describes the isolation, structure elucidation and antimicrobial activities of compound R2. Details on the isolation and the taxonomy of the producing organism Streptosporangium sp. Sg3 were described in a previous paper.11 To isolate compound R2, Streptosporangium sp. Sg3 was cultivated at 30 1C for 9 days in Erlenmeyer flasks (500 ml) containing 100 ml of ISP2 broth (yeast extract 4 g, malt extract 10 g, glucose 4 g, in 1 l distilled water, pH 7.2) on a rotary shaker (250 r.p.m.). The cultures (8 l) were centrifuged and filtered to remove mycelium. The culture filtrate was extracted with an equal volume of n-butanol to generate a crude extract (1.9 g). The latter was fractionated by size exclusion chromatography on Sephadex LH-20 (75% MeOH in H2O), resulting in five fractions, I–V. Fraction IV including R2, was of red color and exhibited an antibacterial activity. It was subjected to semipreparative reversed-phase HPLC using an Interchim UP5ODB column (250 7.8 mm) (Interchim, Montlucon, France) and developed using a continuous grade from 20 to 75% MeOH in H2O (UV detection at 220 nm), yielding three active fractions (1, 2, 3). The major peak 2 with the main antibacterial activity was subjected to repeated HPLC to yield 3.5 mg of compound R2. Compound R2 was obtained as a red powder (optical rotation [a]D +56 (c 0.11, MeOH). The ESI-MS spectrum contained an ion peak at m/z 475.1 [M–H] , and its molecular formula was determined by HRESI-MS analysis as C26H19O9 (calcd 475.43 for (M–H) , found 475.43). The UV absorption maximum at 535 nm was because of the red color and suggested a quinone chromophore. Absorptions at 3259, 2949 and 1721 cm 1 in the IR spectrum of R2 were characteristic of hydroxy, methyl and carbonyl groups, respectively. R2 was soluble in MeOH and DMSO, and insoluble in chloroform, n-hexane and H2O. The structure of R2 (Figure 1) was determined by 1H and 13C NMR spectroscopy and by using 1H–1H COSY45, 1H–13C HMQC and 1H–13C HMBC experiments. The 1H and 13C chemical shifts of compound R2 are given in Table 1. The 13C and Heteronuclear SingleQuantum Correlation spectra showed 26 carbon signals with a large number of quaternary carbons (17 out of 26). From the 13C data, it was possible to discern two keto-carbonyl groups (dc 188.4 and 186.5), one carboxylic acid group (dc 174.1), 19 sp2-hybridized carbons (dc from 160.2 to 114.7), two sp3-hybridized carbons bearing an electronegative heteroatom (dc 73.0 and 72.5), one sp3-hybridized carbon (dc 22.6) and two methyl groups (dc 22.4 and 12.4). In CD3OD, the 1H NMR spectrum revealed two ortho-coupled aromatic protons (dH 7.82 and 7.66, 2H, J1⁄47.5 Hz), two aromatic protons (dH 8.24 and 7.02, 2H, s), an AB system (dH 4.45 and 4.36, JAB1⁄410.7 Hz), an ethyl group (dH 2.83 and 1.32, 5H, J1⁄47.4 Hz) and a methyl group (dH 2.70, 3H, s). In DMSO, NMR signals were significantly broader but the