Biofilm formation and regulation of salicylic acid-inducible genes expression in Arabidopsis by Algerian indigenous bacteria from wheat and potatoes rhizospheres in semi-arid Sétif region.

45 bacterial isolates from potatoes and wheat rhizospheres near Sétif (Algeria) pre-selected for their antagonistic activity against three fungal plant pathogens, two necrotrophic Fusarium solani var. coeruleum and Phytophtora infestans, and a systemic F. oxysporum f. sp. albedinis. Molecular typing of the isolates showed abundance of Bacillus compared to Pseudomonas. Some of the tested strains have shown very high biofilm formation. Among the 24 Gram-positive bacilli screened for four cyclic lipopeptides genes, some isolates harbor two or more genes, while others have a single gene or have none. Four selected isolates were able to regulate the expression of six defense-related genes in Arabidopsis and produce salicylic acid. Upon the features assessed in this study, strain B. amyloliquefaciens A16 was selected for a subsequent use as seed treatment and biocontrol agent in semi-arid region fields. This strain showed important biofilm formation, regulation of Arabidopsis defenses, and harbored three cLPs genes.

Algerian propolis extracts: Chemical composition, bactericidal activity and in vitro effects on gilthead seabream innate immune responses.

Propolis has been used as a medicinal agent for centuries. The chemical composition of four propolis samples collected from four locations of the Sétif region, Algeria, using gas chromatography-mass spectrometry was determined. More than 20 compounds and from 30 to 35 compounds were identified in the aqueous and ethanolic extracts, respectively. Furthermore, the antimicrobial activity of the propolis extracts against two marine pathogenic bacteria was evaluated. Finally, the in vitro effects of propolis on gilthead seabream (Sparus aurata L.) leucocyte activities were measured. The bactericidal activity of ethanolic extracts was very high against Shewanella putrefaciens, average against Photobacterium damselae and very low against Vibrio harveyi. The lowest bactericidal activity was always that found for the aqueous extracts. When the viability of gilthead seabream head-kidney leucocytes was measured after 30 min' incubation with the different extracts, both the ethanolic and aqueous extracts of one of the propolis samples (from Babor) and the aqueous extract of another (from Ain-Abbassa) provoked a significant decrease in cell viability when used at concentrations of 100 and 200 µg ml-1. Furthermore, significant inhibitory effects were recorded on leucocyte respiratory burst activity when isolated leucocytes where preincubated with the extracts. This effect was dose-dependent in all cases except when extracts from a third propolis sample (from Boutaleb) were used. Our findings suggest that some of Algerian propolis extracts have bactericidal activity against important bacterial pathogens in seabream and significantly modulate in vitro leucocyte activities, confirming their potential as a source of new natural biocides and/or immunomodulators in aquaculture practice.