Recherche de nouvelles potentialités de bactéries du genre Bacillus pour l’agriculture et l’agroalimentaire

Abstract

The exploration of samples obtained from diverse environments of Eastern Algeria (a salt lake of Ain M’lila and the rhizosphere of an adjacent plant; the water of a thermal source of Oued El-Athmanya and the environing soil and the rhizosphere of Calendula officinalis, cultivated in a greenhouse in Setif) allowed the obtaining of 39 isolates of Bacillus and Paenibacillus genera. 28 % of these isolates are screened for their capacity to inhibit the growth of some phytopathogenic fungi as: Alternaria alternata, Aspergillus niger, Botrytis cinerea, Cladosporium cucumerinium, Fusarium oxysporium and Fusarium sp. The inhibition rate developed by the screened isolates against F. oxysporium and B. cinerea varies between 39% and 84% according to the isolate. The molecular identification of the screened bacteria by 16S-DNA and gyrase-A gene analysis showes that strains isolated from Ain M’lila are identified as B. amyloliquefaciens, those isolated from Oued El Athmanya belongs to B. amyloliquefaciens, B. atrophaeus and B. mojavensis, and finally, bacteria isolated from C. officinalis rhizosphere are B. velezensis, Paenibacillus polymyxa, B. amyloliquefaciens and B. subtilis subsp. spizezenii. The screened strains develope, in flasks conditions, important sporulation yields varying between 8 x108 and 27x108 spores/ml, while, the sporulation yield of P. polymyxa is insignificant. Only B. amyloliquefaciens strains are able to produce protease. However, the cellulase activity is observed in all Bacillus species studied here, except the B. atrophaeus which is the sole strain able to produce chitinase. All Bacillus species have the same capacity to produce the three lipopeptides families (iturin, fengycin and surfactin), siderophores and the indole 3 acetic acid (IAA). In contrast, P. polymyxa (18SRTS) produces in the same experimental conditions the best IAA concentration reaching 54µg/ml. Moreover, it is to highlight that B. amyloliquefaciens strains isolated from a salt lake and a thermal source produce new fengycin variants. In fact, it has been demonstrated that B. amyloliquefaciens (ET), produces new homologues of fengycin A and B, having fatty acid chain with 20 and 18 carbon atoms, respectively, and two new fengycin variants (fengycin X and Y) with peptide cycle whose the structure differs from that of conventional fengycins. The antifungal activity of some strains (B. amyloliquefaciens (ET), B. atrophaeus (6SEL), B. mojavensis (9SEL), B. amyloliquefaciens (9SRTS) and B. subtilis subsp. spizezenii (23SRTS)) on solid medium based on root exudates of tomato, zucchini and bean, obtained at different temperatures is observed, against A. alternata and F. oxysporium. In addition, B. atrophaeus (6SEL), B. amyloliquefaciens (9SRTS) and B. subtilis subsp. spizezenii (23SRTS) produced at the industrial scale, showe an appreciable alive cells concentration after lyophilization. Furthermore, the in situ test of these strains under greenhouse and field conditions, on chickpea, reveale their interesting phytostimulation and biocontrol capacities, which largely justify the objective assigned by this research.