Actinobacteria are found spread widely in nature and particular attention is given to their role in the production of various bioactive secondary metabolites. Tests on soil samples show that there can be a diversity of actinomycetes depending on the climate, the area it is growing in, how dry the soil is, and the quality of the soil. However, it was agreed after tests in Yunnan, China, that the genus Streptomyces sp. is most important in ecological function, representing up to 90% of all soil actinomycetes, and therefore helping to show the important characteristics needed of the soil actinomycete population. Streptomycete compounds are used for other biological activities, not just for antibiotics. It has been found that metabolites can be broadly divided into four classes: (1) regulatory activities in compounds, these include consideration of growth factors, morphogenic agents and siderophores, and plants promoting rhizobia; (2) antagonistic agents, these include antiprotozoans, antibacterials, antifungals, as well as antivirals; (3) agrobiologicals, these include insecticides, pesticides, and herbicides; and (4) pharmacological agents, these include neurological agents, immunomodulators, antitumorals, and enzyme inhibitors. It is found that Streptomyces hygroscopicus is one of the very best examples because it secretes in excess of 180 secondary metabolites to locate simultaneous bioactivities for a given compound. Increasingly, both its agricultural and pharmacological screenings are being used in conjunction with antimicrobial tests and have revealed several unusual aerobiological and therapeutic agents, which were hitherto unknown for biological use as antibiotics. Since streptomycetes are now being used increasingly to screen for antimicrobial activity, reports show the existence of secondary metabolites with other activities that may have been missed. Currently, nearly 17% of biologically active secondary metabolites (nearly 7600 out of 43,000) are known from streptomycetes. It has been found that soil streptomycetes are the main source used by bioactive secondary metabolites. However, recently there have been many and varied types of structurally unique and biologically active secondary metabolites found and obtained from marine actinomycetes, including those from the genus Streptomyces. Also, compounds that are synthesized by streptomycetes exhibit extreme chemical diversity. Diverse form made from from simple amino acid

No abstract

Among 131 rhizobacteria isolates, 29 potentially antagonistic strains were screened in in vitro assays. The five antagonistic Bacillus spp. Rb29, Rb6, Rb12, Rb4, and Rb15 showed the most inhibitory effect against FOC1 (from 25.63 to 71.11%), mycelial growth, and FOC2 (from 28.43 to 60.65%) in vitro. Results also revealed that production of volatile metabolite, components and inhibition of the test pathogen by volatile metabolites varied among different antagonistic rhizobacteria. Isolates Rb29, Rb6, Rb12, Rb4, and Rb15 produced more volatile metabolites which inhibited mycelial FOC growth by 40%. Chickpea Fusarium wilt severity caused by FOC1 was reduced from 60 to 99% in the susceptible cultivar ILC 482 treated with antagonistic Bacillus spp. (Rb29, Rb6, Rb12, Rb4, and Rb15) in pot assays and by 98, 81, 68, 64, 57.20%, respectively, in the field trials. As for their beneficial effects on disease control, the results revealed that Bacillus spp. may improve plant growth and disease control.

Different desert truffles, collected from Algerian Saharan soils, were identified and their capacity to produce bioactive substances with antimicrobial activity was analyzed. Based on morphological characterization using Melzer's reagent staining, the collected strains were identified as Terfezia arenaria. The bioactive substances from T. arenaria were extracted using the following techniques: maceration with methanol and Soxhlet with dichloromethane. The former led to a yield much higher than that of the latter (i.e., 15% and 0.48%, respectively). Both extracts presented antifungal activities against all the tested strains (i.e., A. niger, Penicillium sp., and C. albicans). However, the dichloromethane extracts showed much higher antibacterial activities against all the tested bacteria (i.e., S. aureus, E. faecalis, E. coli, and P. aeruginosa) than the methanol extracts. The thin layer chromatography of both extracts confirmed the presence of polyphenols and flavonoids.

Aims: The capacity of some soil microorganisms to solubilize in soil is an important activity exhibited by plant growth promoting rhizobacteria (PGPR) to increase plant performance. This study aimed at isolation and selection of phosphate solubilizing bacteria from saline soil and in vitro evaluation of their plant growth promoting traits. Methodology and results: Phosphate solubilizing bacteria isolated from wheat rhizosphere, of saline soil in western region of Algeria were tested for their plant growth promoting traits such us indole acetic acid (IAA), hydrogen cyanide (HCN), siderophore and ammonia production and their ability to fix nitrogen. Among 104 bacterial isolates, 41 were selected for their phosphate solubilizing activity using tricalcium phosphate (TCP) as a sole phosphorus source. IAA production was shown by almost all the bacterial isolates. Twelve isolates were recorded positive for HCN production, 32 produced siderophore and 31 were able to fix nitrogen. The most dominant phosphate solubilizing bacteria found were identified as Pseudomonas followed by Aeromomas hydrophila Bacillus sp. and Burkholderia cepacia. Conclusion: Phosphate solubilizing bacteria that were isolated from saline soil showed a high potential in to producing growth promoting traits and can be used as inoculants to increase the phosphorus uptake by plants.

Purpose: To investigate the intra-specific variations in eleven Fusarium oxysporum isolates from infected date palm using pathogenicity and molecular methods. Methods: Eleven isolates of Fusarium oxysporum obtained from infected date palms in the southwest region of Algeria were subjected to confirmatory test using a specific polymerase chain reaction (PCR) technique with the primer pairs, TL3-FOA28 and BIO3-FOA1. Polymorphism in the 5' domain of the large subunit rRNA was investigated. Small libraries of the domain, amplified by the primer pair, LR3/LROR, were constructed and the inserts sequenced. Results: The 11 isolates of Fusarium oxysporum collected from the infected date palm were confirmed as Fusarium oxysporun f. sp albedinis. Results from the investigation of polymorphism in the 5' domain of the large subunit rRNA revealed that the sequences were 100 % homologous or extremely close (> 99.4 %, differing by no more than one to three nucleotides) to several Fusarium oxysporum sequences. In addition, F. inflexum (U34548.1) was highly homologous to one of the F. oxysporum f. sp. albedinis. Conclusion: The sequences of the 11 isolates are almost 100 % homologous to several F. oxysporum species. It is noteworthy that a sequence highly homologous to one of the F. oxysporum f. sp. albedinis is obtainable from a different species, F. inflexum (U34548.1).

This study concerned the characterization of endomycorrhizal fungi associated to a variety of olive tree which is endemic to Algeria ; the Sigoise variety (Olea europea L.). The study was carried out in western Algeria where the cultivation of this variety is dominant. As methodological approaches, we used techniques that allow to highlight several biological aspects of endomycorrhization. Indeed, the estimation of the natural endomycorrhizal infection in the roots of olive trees was carried out as well as the study of the endomycorrhizal potential of the soil (EMP). Also, an estimation and identification of natural endomycorrhizal fungi of the soil and their effects on the sanitary state (growth) of the olive plants were undertaken in the greenhouse. In results, microscopic examinations of olive tree root fragments revealed a very high mycorrhization rate (more than 80%) with the presence of different structures characteristic of arbuscular endomycorrhizae : arbuscules, vesicles and pellets, independently of the age and season of sampling. Morphological characterization of fungal spores, isolated from rhizospheric soils of olive tree, revealed the presence of three genera belonging to the order of Glomales: Glomus sp., Acaulospora sp. and Gigaspora sp. with a predominance of Glomus. Moreover, the growth parameters of the aerial and underground parts of the olive plants were positively affected after inoculation, which reflects a good sanitary condition of the plants. In conclusion, our work provided additional knowledge on the controlled mycorrhization of olive plants and opened interesting perspectives for the application of this biotechnology to the production of olive plants in greenhouses.