SummaryBacteria respond to diverse growth-limiting stresses by producing a large set of general stress proteins. In Bacillus subtilis and related Gram-positive pathogens, this

The infectious processes of the Frankia-Alnus and Rhizobium-legume symbioses present strong similarities, suggesting the existence of analogies between Frankia root hair deforming factor and rhizobia Nod factors. Biochemical and functional analogies were tested using ACoN24d Frankia strain. The putative chitin-like nature of the Frankia deforming factor was explored by (i) gas chromatography coupled to mass spectrometry and thin layer chromatography, after radioactive labeling of the culture for detection of chitin oligomers, and (ii) following the root hair deforming activity of the supernatant after discriminating treatments (temperature, chitinase, butanol extraction). In parallel, the functional analogy was questioned by testing the mitotic activity of the Frankia supernatant onAlnus glutinosa (L.) roots. The implication in the symbiotic process of the Frankia factor was indirectly explored by testing the effect of a nodulation inhibitor (combined nitrogen) on root hair deformation. The studies of the combined nitrogen effect on root hair deformation indicate that the deformation induced in vitro by the Frankia factor is linked to the symbiotic process. Moreover, the various approaches used suggest that rhizobia Nod factors and Frankia root hair deforming factor are two structurally divergent symbiotic factors. However, functionnal differences between Frankia root hair factor and the Nod factors have to be confirmed.Key words: Frankia, root hair deforming factor, Nod factor, actinorhizal plants.

The lin genes encode the gamma-hexachlorocyclohexane (gamma-HCH or lindane) catabolic pathway in lindane-degrading strains. The location and stability of these genes have been explored in the lindane-degrading Sphingobium francense strain Sp+, and in two non-lindane-degrading mutants (Sp1- and Sp2-). The lin genes, linA, linB, linE and linX were localized by hybridization on three of the six plasmids of the S. francense strain Sp+ showing dispersal within the genome. The linC gene was detected by PCR, but was not detected by hybridization on any of the plasmids. The hybridization of the linA and linX genes was negative with the two non-lindane-degrading mutants S. francense strains, Sp1- and Sp2-. The dynamic of this genome associated with gene loss and acquisition, and plasmid rearrangement was explored by a search for associated insertion sequences. A new insertion sequence, ISSppa4, belonging to the IS21 family was detected and compared with IS6100 and ISsp1. Insertion sequence localization was explored on different hybridization patterns (plasmid, total genome) with the lindane-degrading Sp+ strain and the two non-degrading derivatives (Sp1-, Sp2-). Insertion sequence movement and plasmid rearrangement could explain the emergence of the non-lindane-degrading mutants.

Artificial transformation is typically performed in the laboratory by using either a chemical (CaCl 2 ) or an electrical (electroporation) method. However, laboratory-scale lightning has been shown recently to electrotransform Escherichia coli strain DH10B in soil. In this paper, we report on the isolation of two "lightningcompetent" soil bacteria after direct electroporation of the Nycodenz bacterial ring extracted from prairie soil in the presence of the pBHCRec plasmid (Tc r , Sp r , Sm r ). The electrotransformability of the isolated bacteria was measured both in vitro (by electroporation cuvette) and in situ (by lightning in soil microcosm) and then compared to those of E. coli DH10B and Pseudomonas fluorescens C7R12. The electrotransformation frequencies measured reached 10 ؊3 to 10 ؊4 by electroporation and 10 ؊4 to 10 ؊5 by simulated lightning, while no transformation was observed in the absence of electrical current. Two of the isolated lightning-competent soil bacteria were identified as Pseudomonas sp. strains.