Phosphate and potash solubilizing bacteria from Moroccan phosphate mine showing antagonism to bacterial canker agent and inducing effective tomato growth promotion.

Most agricultural soils are facing limited phosphorus availability that challenges modern agriculture. Phosphate solubilizing microbia (PSM) has been explored extensively as potential biofertilizers for plant growth and nutrition, and harnessing phosphate rich areas could provide such beneficial microorganisms. Isolation of PSM from Moroccan rock phosphate led to the selection of two bacterial isolates, Bg22c and Bg32c, showing high solubilization potential. The two isolates were also tested for other in vitro PGPR effects and compared to a non-phosphate solubilizing bacterium Bg15d. In addition to phosphates, Bg22c and Bg32c were able to solubilize insoluble potassium and zinc forms (P, K, and Zn solubilizers) and produce indole-acetic acid (IAA). Mechanisms of solubilization involved production of organic acids as demonstrated by HPLC. In vitro, the isolates Bg22c and Bg15d were able to antagonize the phytopathogenic bacteria Clavibacter michiganensis subsp. michiganensis, causal agent of tomato bacterial canker disease. Phenotypic and molecular identification by 16S rDNA sequencing demonstrated delineation of Bg32c and Bg15d as members of the genus Pseudomonas and Bg22c as member of the genus Serratia. The two isolates Bg22c and Bg32c were further tested either alone or in a consortium and compared to the non-P, K, and Zn solubilizing Pseudomonas strain Bg15d for their efficacy to promote tomato growth and yield. They were also compared to treatment with a conventional NPK fertilizer. Under greenhouse conditions, Pseudomonas strain Bg32c remarkably improved the growth of whole plant height, root length, shoot and root weight, number of leaves and fruits, as well as fruit fresh weight. This strain also induced stomatal conductance enhancement. The strain also improved total soluble phenolic compounds, total sugars, protein, phosphorus and phenolic compounds contents compared to the negative control. All increases were more pronounced in plants inoculated with strain Bg32c in comparison with control and strain Bg15d. The strain Bg32c could be considered a potential candidate for formulation of a biofertilizer in order to improve tomato growth.

Streptomyces thinghirensis sp. nov., isolated from rhizosphere soil of Vitis vinifera.

A novel actinomycete, strain S10(T), was isolated from rhizosphere soil of wild Vitis vinifera in Thinghir, Ouarzazate Province, Southern Morocco. The taxonomic status of this strain was established using a polyphasic approach. Strain S10(T) had white-grey aerial mycelium with long, spiral spore chains bearing smooth surfaced spores and produced a yellow diffusible pigment. Chemotaxonomic analyses showed that the cell wall of strain S10(T) contained ll-diaminopimelic acid and glycine. Phylogenetic analysis based on the almost complete 16S rRNA gene sequence indicated that strain S10(T) belonged to the Group I streptomycetes, branching off next to Streptomyces marokkonensis LMG 23016(T) from the Streptomyces violaceoruber group. DNA-DNA relatedness and phenotypic data distinguished strain S10(T) from the phylogenetically closest related type strains. It is therefore proposed that strain S10(T) (=CCMM B35(T)=DSM 41919(T)) represents the type strain of a novel species of the genus Streptomyces, for which the name Streptomyces thinghirensis sp. nov. is proposed.

Streptomyces marokkonensis sp. nov., isolated from rhizosphere soil of Argania spinosa L.

The novel actinomycete strain Ap1(T) was isolated from rhizosphere soil of the argan tree (Argania spinosa L.) in the south of Morocco. Strain Ap1(T) has been reported as a novel producer of the pentaene polyene macrolide isochainin, which strongly inhibits the growth of pathogenic yeasts and phytopathogenic fungi. Strain Ap1(T) shows a greyish-white aerial mycelium with chains of smooth-surfaced spores of the Spiralis type and a cell wall containing ll-diaminopimelic acid. Based on chemotaxonomy and morphological features, strain Ap1(T) was identified as a member of the genus Streptomyces. 16S rRNA gene sequence similarities based on almost-complete 16S rRNA gene sequences showed that strain Ap1(T) is closely associated with members of the Streptomyces violaceoruber species group (S. violaceoruber, S. coelescens, S. violaceorubidus, 'S. caesius', 'S. lividans', S. violaceolatus and S. humiferus) and others (Streptomyces aurantiogriseus, S. lienomycini, S. chattanoogensis, S. rubrogriseus and S. tendae). However, protein profiling, DNA-DNA hybridization and BOX-PCR fingerprinting proved a relationship above the species level. In addition, the phenotype also allowed for the differentiation of strain Ap1(T) from its closest neighbours. As a result of this polyphasic approach, we conclude that strain Ap1(T) represents a novel species of the genus Streptomyces, for which the name Streptomyces marokkonensis sp. nov. is proposed. The type strain is Ap1(T) (=R-22003(T) =LMG 23016(T) =DSM 41918(T)).

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.