V. Leclere

Effect of pps disruption and constitutive expression of srfA on surfactin productivity, spreading and antagonistic properties of Bacillus subtilis 168 derivatives

Aims:u2002 To analyse the effects of plipastatin operon disruption and constitutive expression of surfactin operon in Bacillus subtilis 168 on surfactin productivity, in vitro invasive growth and antagonism against fungi.

Development of a biological test to evaluate the bioavailability of iron in culture media

Aims:u2002 To develop an easy‐to‐use and pathogen‐free protocol giving reliable information on the bioavailability of iron in a medium.

Nonribosomal peptide synthetase with a unique iterative-alternative-optional mechanism catalyzes amonabactin synthesis in Aeromonas

Based on the exploration of data generated by genome sequencing, a bioinformatics approach has been chosen to identify the biosynthetic pathway of the siderophores produced by Aeromonas species. The amonabactins, considered as a virulence factor, represent a family of four variants of catechol peptidic siderophores containing Dhb, Lys, Gly, and an aromatic residue either Trp or Phe in a D-configuration. The synthesis operon is constituted of seven genes named amoCEBFAGH and is iron-regulated. The cluster includes genes encoding proteins involved in the synthesis and incorporation of the Dhb monomer, and genes encoding specific nonribosomal peptide synthetases, which are responsible for the building of the peptidic moiety. The amonabactin assembly line displays a still so far not described atypical mode of synthesis that is iterative, alternative, and optional. A disruption mutant in the adenylation domain of AmoG was unable to synthesize any amonabactin and to grow in iron stress conditions while a deletion of amoH resulted in the production of only two over the four forms. The amo cluster is widespread among most of the Aeromonas species, only few species produces the enterobactin siderophore.

Bioinformatics tools for the discovery of new lipopeptides with biocontrol applications

As conventional or chemical pesticides have negative impact on environment and health of both farmer and consumers, it becomes relevant to develop alternative solutions to limit their use. In this context, innovative strategies to accelerate the development of biocontrol agents are welcome. For a decade of years, it has been demonstrated that lipopeptides are very efficient weapons against fungi responsible for crop diseases. Lipopeptides are secondary metabolites, produced by many microorganisms including beneficial rhizobacteria. The lipopeptide biosynthetic pathways include nonribosomal peptide synthetases. These modular enzymatic complexes work as assembly lines to build the peptides step by step, leading to the production of original peptide compounds with specific features as the presence of non proteinogenic monomers and cyclic and branched structures. In this paper, Florine and Norine bioinformatics tools, especially dedicated to non-ribosomal synthetases and their products are presented. Their use is mainly focused on the discovery of lipopeptides produced by Bacillus or Pseudomonas because they seem to represent a versatile reservoir of active secondary metabolites with promising activities for applications in phytosanitary area.

Lipopeptide biodiversity in antifungal Bacillus strains isolated from Algeria

Several Bacillus strains have been well studied for their ability to control soil-borne plant diseases. This property is linked to the production of several families of lipopeptides. Depending of their structure, these compounds show antifungal and/or plant systemic resistance inducing activities. In this work, the biodiversity of lipopeptides produced by different antifungal Bacillus strains isolated from seeds, rhizospheric, and non-rhizospheric soils in Algeria was analyzed. Sixteen active strains were characterized by PCR for their content in genes involved in lipopeptide biosynthesis and by MALDI-ToF for their lipopeptide production, revealing a high biodiversity of products. The difficulty to detect kurstakin genes led us to design two new sets of specific primers. An interesting potential of antifungal activity and the synthesis of two forms of fengycins differing in the eighth amino acid (Gln/Glu) were found from the strain 8. Investigation of its genome led to the finding of an adenylation domain of the fengycin synthetase predicted to activate the glutamate residue instead of the glutamine one. According to the comparison of both the results of MALDI-ToF-MS and genome analysis, it was concluded that this adenylation domain could activate both residues at the same time. This study highlighted that the richness of the Algerian ecosystems in Bacillus strains is able to produce: surfactin, pumilacidin, lichenysin, kurstakin, and different types of fengycins.