Strain-specific chemotaxis of Azospirillum spp

Abstract

Chemotactic responses of three Azospirillum strains originating from different host plants were compared to examine the possible role of chemotaxis in the adaptation of these bacteria to their respective hosts. The chemotaxis to several sugars, amino acids, and organic acids was determined qualitatively by an agar plate assay and quantitatively by a channeled-chamber technique. High chemotactic ratios, up to 40, were obtained with the latter technique. The chemotactic response did not rely upon the ability of the bacteria to metabolize the attractant. Rather, it depended on the attractant concentration and stereoconfiguration. Chemotaxis was found to be strain specific. Differences were particularly observed between a wheat isolate and strains originating from the C4-pathway plants maize and Leptochloa fusca. In contrast to the other two strains, the wheat isolate was strongly attracted to D-fructose, L-aspartate, citrate, and oxalate. The other strains showed maximal attraction to L-malate. The chemotactic responses to organic acids partially correlate with the exudation of these acids by the respective host plants. Additionally, a heat-labile, high-molecular-weight attractant was found in the root exudates of L. fusca, which specifically attracted the homologous Azospirilum strain. It is proposed that strain-specific chemotaxis probably reflects an adaptation of Azospirillum spp. to the conditions provided by the host plant and contributes to the initiation of the association process.

Global expression analysis of the response to microaerobiosis reveals an important cue for endophytic establishment of Azoarcus sp. BH72

“…For these, strain BH72 was grown in an oxygen‐controlled bioreactor (Biostat B; B. Braun Melsungen AG, Melsungen, Germany) at 37°C with stirring at 600 r.p.m. under microaerobic (0.3% oxygen concentration) or aerobic conditions (21% oxygen concentration) in nitrogen‐free SM (Reinhold et al ., ), always supplemented with 10 mM ammonium chloride as N source. The pH was stably maintained at 6.95 throughout the duration of each run.…”

“…For the determination of growth rates, or membrane analysis, a malate mineral medium (SM) (Reinhold et al ., ) containing 0.01% of yeast extract and 0.05% of NH 4 Cl was used. A total of 100 ml of culture were incubated in 1 l Erlenmeyer flasks at 200 r.p.m.…”

Transcriptomic analysis of responses to exudates reveal genes required for rhizosphere competence of the endophyte Azoarcus sp. strain BH72

“…Escherichia coli strains were grown at 37°C on LB medium or LB agar plates (Sambrook et al, 1989). The Azoarcus strains were routinely grown aerobically at 37°C in VM-ethanol medium (Hurek et al, 1995) or SM medium containing combined nitrogen (Reinhold et al, 1985). For electroporation and conjugation, Azoarcus strains were grown aerobically at 37°C in VM medium with DL-malic acid (Reinhold et al, 1985;Reinhold-Hurek et al, 1993b) with a modification of 0.3% bacto peptone instead of beef extract and without biotin.…”

Quantitative estimation of complex phosphate - solubilization by immobilized or free Azospirillum Lipoferum (H3) as vital vaccine in Pikovskaya broth (PVK) medium

“…Moreover, the cultural and morphological tests and some biochemical tests were proceeded, for example the acidification of different carbon sources by the tested bacteria according to the level of acidification of the pH indicator, (bromothymol-blue) to colour the reaction. The preference of the organic acids by different Azospirillum species was reported by Reinhold et al, (1985), and can be explained on the basis that organic acids were the major source of nutrients for microflora in the rhizosphere (Curl and Truelove, 1986). All strains were positive in nitrate reductase, catalse and motility activities and the isolates were negative in gelatin and starch hydrolysis.…”