Isolation and characterization of wastewater sand filter actinomycetes

One hundred twenty-two different actinomycete strains were isolated from sample collected from several depths of the Marrakech wastewater infiltration-percolation system. To evaluate the antimicrobial effect of the different actinomycetes recovered, eleven wastewater-associated micro-organisms known as human potential pathogens were used. Results showed that 44 isolates had an in vitro inhibitory effect toward at least seven of the indicator microorganisms while only five active strains inhibited all these pathogens. All five selected active isolates belonged to the genus Streptomyces. Three were identified as Streptomyces violaceorubidus. These isolates showed the broad activity spectrum against a wastewater-associated pathogenic yeast (Candida albicans), Gram-negative (Salmonella sp. CCMM B₁₇) and Gram-positive (Staphylococcus aureus CCMM B₃). These findings indicate the potential involvement of antagonistic actinomycetes in the removal of wastewater-associated pathogens.     

Actinomycetes from Moroccan habitats: isolation and screening for cytotoxic activities

In our screening for actinomycetes showing cytotoxic activities, 8 samples were collected from various Moroccan habitats, 136 isolates were tested for their capacity to produce antibacterial compounds against gram positive bacteria. Thirty-seven strains of these isolates were active against Gram-positive bacteria. Using the following steps of primary screening: antibacterial activity, confrontation between the isolates and toxicity to Artemia salina; fifteen different isolates were used for further investigation. The aqueous extracts of Streptomyces sp. T5 and Streptomyces sp. AS8 were selected for their cytotoxic activity against Hep2, BSR and P815 cell lines, and two active compounds were observed on HPLC. The two isolates exhibited high activity against human cancer cell lines and were inactive on PBMC cell lines. Furthermore, the Streptomyces sp. T5 extract showed a proliferative activity.     

Electrophysiological Responses to Fusaric Acid of Root Hairs from Seedlings of Date Palm-susceptible and -resistant to Fusarium oxysporum f. sp. albedinis

Bayoud, a vascular wilt of date palm caused by Fusarium oxysporum f. sp. albedinis (Foa), is the most devastating disease in palm groves of north Africa. Although Foa is able to induce resistance mechanisms in its host plant, no data are available on the early responses of the root cells. Fusaric acid (FA) is the main toxin found in culture filtrates from Foa aggressive strains. This phytotoxin induces modifications of membrane permeability or membrane potential in various cell types and could thus be involved in the early steps of signal exchange between the pathogen and the plant. We showed an early differential behaviour of the disease‐resistant and ‐susceptible cultivars from date palm when challenged by FA. This response could be due to a differential sensitivity of H⁺‐ATPases to FA.     

Rock phosphate-solubilizing Actinomycetes: screening for plant growth-promoting activities

In order to select Actinobacteria that could improve plant growth and thus agricultural yield, we assessed different plant growth promoting (PGP) abilities of eight rock phosphate (RP)-solubilizing Actinomycete isolates originating from Moroccan phosphate mines. Six of these strains were able to grow on root exudates of the wheat plant as sole nutrient sources and were efficiently releasing soluble phosphate from RP. These strains also inhibited the growth of potentially phytopathogenic fungi, bacteria (Gram +/−) or yeasts. Five of these strains produced indoleacetic acid and four showed endophytic properties. When these strains were grown, in the presence of the wheat plant, in a synthetic minimum medium (SMM) containing insoluble RP as unique phosphate source or in soil experiment, the most active RP-solubilizing strains had the highest stimulatory effect on the production of plant biomass. The most efficient strain Streptomyces griseus-related strain (BH₇), stimulated aerial growth of the plant more than 70% in test tubes and more than 30% in RP soil compared to the non-inoculated control treatment. This study demonstrated that our selected Actinomycete strains could be used for the development of novel, non-polluting; farming practices by entering in the formulation of novel biofertilizer and biocontrol products constituted by spores and/or mycelium of the ad hoc Actinobacteria in association with pulverized RP.     

Novel Production of Isochainin by a Strain of <Emphasis Type="Italic">Streptomyces </Emphasis>sp<Emphasis Type="Italic">.</Emphasis> Isolated from Rhizosphere Soil of the Indigenous Moroccan Plant <Emphasis Type="Italic">Argania Spinosa</Emphasis> L

Summary An actinomycete strain (designated Ap1) isolated from the rhizosphere soil of Argania spinosa L. strongly inhibited the growth of two plant pathogens: Fusarium oxysporum f.sp. albedinis and Verticillium dahliae. The spore morphology suggested that the Ap1 strain belonged to the genus Streptomyces. The antifungal compound produced by Ap1 was purified by HPLC and identified as the polyene macrolide, isochainin, by NMR and mass spectroscopy. Ap1 showed normal biosynthesis of isochainin in comparison with S. cellulosae ATTC 12625, in which precursor-directed biosynthesis by feeding ethyl (Z)-16-phenylhexadec-9-enoate to the culture medium is required. In addition, Streptomyces sp. strain Ap1 produces isochainin with a 6.5-fold higher concentration than Streptomyces cellulosae ATTC 12625.     

Pril-ampicillin-dextrin-ethanol agar for the isolation and quantification of Aeromonas spp. from polluted environmental waters

Several selective media were evaluated for their suitability for the isolation and quantification of mesophilic Aeromonas species from naturally polluted samples. Satisfactory recoveries were obtained with most of them but only when densities of background microflora were low. When analysed samples were from highly polluted waters, results were inconsistent because they did not give quantitative recovery of mesophilic aeromonads or they did not permit ready differentiation of Aeromonas species from the competitive bacteria. A new medium was developed on the basis of the combination of some positive aspects of several published media, pril-ampicillin-dextrin-ethanol (PADE) agar. The medium employs dextrin (Merck 3006) as a fermentable carbohydrate and pril, ampicillin and ethanol as inhibitory substances. Recovery on PADE agar from suspensions of 15 tested strains of Aeromonas prepared from pure cultures was excellent. The confirmation rate of typical colonies designated Aeromonas spp. isolated from polluted samples exceeded 90%. Recoveries of stressed aeromonad strains on both PADE agar and a non-selective medium (TSA) did not show any significant difference ( P 0.05). PADE agar was more reliable for quantitative recovery of mesophilic aeromonads than the other selective media because of its characteristics: (i) inhibition of the swarming of Proteus , (ii) good reduction of the background, (iii) inhibition of the over growth of Klebsiella spp., (iv) absence of NaCl makes it unfavourable for the growth of halophilic vibrios, (v) combination of two pH indicators permitted a very easy differentiation between Aeromonas colonies and the competitive microflora. The medium can also be used for isolation of aeromonads from various sources by membrane filtration.     

A putative role for fusaric acid in biocontrol of the parasitic angiosperm Orobanche ramosa

Fusarium spp. are ubiquitous fungi found in soil worldwide as both pathogenic and nonpathogenic strains. The signals leading to disease or the absence of disease are poorly understood. We recently showed that fusaric acid (FA), a nonspecific toxin produced by most Fusarium spp., could elicit various plant defense responses at 100 nM without toxic effect. In this study, we checked for the effect of FA on root and root hairs, probable first site of contact between the fungi and the host. Large FA concentrations reduce root and root-hair growth and induce a rapid transient membrane hyperpolarization, followed by a large depolarization, due to the inhibition of H(+)-ATPase currents. Nanomolar concentrations of FA induced only an early transient membrane hyperpolarization of root hairs compatible with the induction of a signal transduction pathway. FA at 10(-7) M failed to induce salicylic acid- and jasmonic acid/ethylene-dependent defense-related genes but inhibited the germination of the angiosperm parasite Orobanche ramosa in contact of FA-pretreated Arabidopsis thaliana seedlings. These data suggest that FA at nontoxic concentrations could activate signal transduction components necessary for plant-defense responses that could contribute to biocontrol activity of Fusarium spp.     

Characterization of rhizospheric soil streptomycetes from Moroccan habitats and their antimicrobial activities

During an investigation on actinomycetes from rhizospheric soils from Moroccan habitats, 131 streptomycetes were recovered, morphologically characterized and assessed for their antimicrobial activity. Eleven isolates were characterized by the absence of an aerial mycelium. According to the colour of aerial mycelium, the rest were grouped into seven main classes, namely, grey, yellow, cream, white, green, red and polymorphic colours (pink, orange or violet). The grey colour class dominated (40%) and the red one was found only in rhizospheric soil of the Moroccan endemic plant Argania spinosa. About one third of the isolates (34%) produced soluble pigments of various colours and 14% produced melanoid pigments. Most of the isolates (83%) were active against one or more of the organisms tested (one gram-negative bacterium, three gram-positive bacteria, three yeasts and two filamentous fungi). Most antibiotic-producing isolates possess red and white colour. Strong antibiosis was exhibited against Streptomyces scabies, Staphylococcus aureus and Bacillus subtilis (75, 68 and 60% respectively), while only 14 and 8% of isolates displayed an activity against Escherichia coli and Verticillium dahliae respectively.     

Early physiological responses of Arabidopsis thaliana cells to fusaric acid: toxic and signalling effects

Fusaric acid (FA) is a toxin produced by Fusarium species. Most studies on FA have reported toxic effects (for example, alteration of cell growth, mitochondrial activity and membrane permeability) at concentrations greater than 10(-5) m. FA participates in fungal pathogenicity by decreasing plant cell viability. However, FA is also produced by nonpathogenic Fusarii, potential biocontrol agents of vascular wilt fusaria. The aim of this study was to determine whether FA, at nontoxic concentrations, could induce plant defence responses. Nontoxic concentrations of FA were determined from cell-growth and O2-uptake measurements on suspensions of Arabidopsis thaliana cells. Ion flux variations were analysed from electrophysiological and pH measurements. H2O2 and cytosolic calcium were quantified by luminescence techniques. FA at nontoxic concentrations (i.e. below 10(-6) m) was able to induce the synthesis of phytoalexin, a classic delayed plant response to pathogen. FA could also induce rapid responses putatively involved in signal transduction, such as the production of reactive oxygen species, and an increase in cytosolic calcium and ion channel current modulations. FA can thus act as an elicitor at nanomolar concentrations.     

Antagonistic actinomycetes from Moroccan soil to control the grapevine gray mold

One hundred and forty-two different actinomycete strains were isolated from rhizosphere soil of Vitis vinifera L. sampled from four Moroccan areas. To evaluate the antifungal effect of the different collected actinomycete isolates, five fungi known to be phytopathogens (Pythium ultimum, Fusarium oxyysporum f. sp. albedinis, Sclerotium rolfsii, Verticillium dahliae and Botrytis cinerea) were used. Results showed that 24 isolates had an in vitro inhibitory effect toward at least 4 of the indicator fungi, but only 9 inhibited all these phytopathogens. These nine isolates were subsequently evaluated individually using in vitro grapevine plantlets for their ability to protect against plant gray mold. We demonstrate here that pre-inoculation of plantlets with these isolates allow them to withstand Botrytis cinerea. Six of these strains were shown to belong to the genus Streptomyces and three to the genus Micromonospora. These findings indicate the potential of developing effective actinomycetes from Moroccan habitats for the biological control of Botrytis cinerea. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.