Climatic Zone and Soil Properties Determine the Biodiversity of the Soil Bacterial Communities Associated to Native Plants from Desert Areas of North-Central Algeria.

Algeria is the largest country in Africa characterized by semi-arid and arid sites, located in the North, and hypersaline zones in the center and South of the country. Several autochthonous plants are well known as medicinal plants, having in common tolerance to aridity, drought and salinity. In their natural environment, they live with a great amount of microbial species that altogether are indicated as plant microbiota, while the plants are now viewed as a "holobiont". In this work, the microbiota of the soil associated to the roots of fourteen economically relevant autochthonous plants from Algeria have been characterized by an innovative metagenomic approach with a dual purpose: (i) to deepen the knowledge of the arid and semi-arid environment and (ii) to characterize the composition of bacterial communities associated with indigenous plants with a strong economic/commercial interest, in order to make possible the improvement of their cultivation. The results presented in this work highlighted specific signatures which are mainly determined by climatic zone and soil properties more than by the plant species.

Deoxynivalenol-producing ability of Fusarium culmorum strains and their impact on infecting barley in Algeria.

The cereal-pathogenic Fusarium culmorum (W.G. Smith), causal agent of various blights and rot diseases, is considered as a chronic fungus of economic concern worldwide including North African countries such as Algeria. This pathogen produces a wide range of mycotoxins, amongst which the type B-trichothecene deoxynivalenol (DON). In addition to its acute and chronic side effects in livestock and humans, DON is believed to play a determinant role in the pathogenesis toward Triticeae. However, regardless its significant occurrence and impact, little is known about trichothecenes-producing ability of F. culmorum infecting cereals in Algeria. The PCR assay based on Tri genes of 12 F. culmorum strains (designated Fc1-Fc12), which were recovered from several cropping areas of North Algeria, revealed their trichothecenes-producing ability with 3-AcDON genotype. The molecular prediction was confirmed by HPLC analysis. All strains were able to produce the toxin at detectable levels. Strains Fc1 and Fc12 were the highest producers of this mycotoxin with 220 and 230 µg g(-1), respectively. The evaluation of pathogenic ability of strains through a barley infesting experiment exhibited the significant disease impact of most strains. Significant correlation between the DON-producing ability of strains and the increase in both disease severity (r = 0.88, P = 0.05) and disease occurrence (r = 0.70, P = 0.05) was observed. Chemotyping of F. culmorum isolates and evaluation of their pathogenic ability are reported for the first time for isolates from Algeria, and highlights the important potential of F. culmorum to contaminate cultivated cereal with DON trichothecenes.

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 12800(T) (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%.

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.

Endophytic actinomycetes from spontaneous plants of Algerian Sahara: indole-3-acetic acid production and tomato plants growth promoting activity.

Twenty-seven endophytic actinomycete strains were isolated from five spontaneous plants well adapted to the poor sandy soil and arid climatic conditions of the Algerian Sahara. Morphological and chemotaxonomical analysis indicated that twenty-two isolates belonged to the Streptomyces genus and the remaining five were non-Streptomyces. All endophytic strains were screened for their ability to produce indole-3-acetic acid (IAA) in vitro on a chemically defined medium. Eighteen strains were able to produce IAA and the maximum production occurred with the Streptomyces sp. PT2 strain. The IAA produced was further extracted, partially purified and confirmed by thin layer chromatography (TLC) analysis. The 16S rDNA sequence analysis and phylogenetic studies indicated that strain PT2 was closely related to Streptomyces enissocaecilis NRRL B 16365(T), Streptomyces rochei NBRC 12908(T) and Streptomyces plicatus NBRC 13071(T), with 99.52 % similarity. The production of IAA was affected by cultural conditions such as temperature, pH, incubation period and L-tryptophan concentration. The highest level of IAA production (127 µg/ml) was obtained by cultivating the Streptomyces sp. PT2 strain in yeast extract-tryptone broth supplemented with 5 mg L-tryptophan/ml at pH 7 and incubated on a rotary shaker (200 rpm) at 30 °C for 5 days. Twenty-four-hour treatment of tomato cv. Marmande seeds with the supernatant culture of Streptomyces sp. PT2 that contained the crude IAA showed the maximum effect in promoting seed germination and root elongation.