Phosphatidylcholine levels of peanut-nodulatingBradyrhizobiumsp. SEMIA 6144 affect cell size and motility

Abstract

Phosphatidylcholine, the major phospholipid in eukaryotes, is found in rhizobia and in many other bacteria interacting with eukaryotic hosts. Phosphatidylcholine has been shown to be required for a successful interaction of Bradyrhizobium japonicum USDA 110 with soybean roots. Our aim was to study the role of bacterial phosphatidylcholine in the Bradyrhizobium-peanut (Arachis hypogaea) symbiosis. Phospholipid N-methyltransferase (Pmt) and minor phosphatidylcholine synthase (Pcs) activities were detected in crude extracts of the peanut-nodulating strain Bradyrhizobium sp. SEMIA 6144. Our results suggest that phosphatidylcholine formation in Bradyrhizobium sp. SEMIA 6144 is mainly due to the phospholipid methylation pathway. Southern blot analysis using pmt- and pcs-probes of B. japonicum USDA 110 revealed a pcs and multiple pmt homologues in Bradyrhizobium sp. SEMIA 6144. A pmtA knockout mutant was constructed in Bradyrhizobium sp. SEMIA 6144 that showed a 50% decrease in the phosphatidylcholine content in comparison with the wild-type strain. The mutant was severely affected in motility and cell size, but formed wild-type-like nodules on its host plant. However, in coinoculation experiments, the pmtA-deficient mutant was less competitive than the wild type, suggesting that wild-type levels of phosphatidylcholine are required for full competitivity of Bradyrhizobium in symbiosis with peanut plants.

Restrictive water condition modifies the root exudates composition during peanut-PGPR interaction and conditions early events, reversing the negative effects on plant growth

“…The relationship between bacterial motility and phosphatidylcholine levels have been previously demonstrated by our working group, showing that a SEMIA6144 mutant in phosphatidylcholine biosynthesis presented reduced motility (Medeot et al, 2010). In our work, the addition of peanuts RE in the culture medium, favored the motility of both microorganisms.…”

“…Bradyrhizobium sp. SEMIA6144 (SEMIA6144 in the rest of the text) was grown in B-medium (Van Brussel et al, 1977;Medeot et al, 2010). Azospirillum brasilense (Az39 in the rest of the text) was grown in NFb (Döbereiner & Day, 1976).…”

ExoS/ChvI Two-Component Signal-Transduction System Activated in the Absence of Bacterial Phosphatidylcholine

“…Swim plates (LB/MC+ medium with 0.3% agar) were pointinoculated with a toothpick and usually incubated for 48 h at 28 • C similarly as described (Medeot et al, 2010). Swimming was assessed qualitatively by examining the circular turbid zone formed by the bacterial cells migrating away from the point of inoculation.…”

Reorganization of Azospirillum brasilense cell membrane is mediated by lipid composition adjustment to maintain optimal fluidity during water deficit

“…Photographs were processed and bacterial size was determined using the axiovision 4.1 software (Carl Zeiss) (Medeot et al . ).…”

“…Bacterial cells from the control and stress treatment groups were stained by Gram staining and observed under a Zeiss microscope (Axiophot Carl Zeiss, Weimar, Germany) equipped with a Canon PC1089 Powershot G6 7.1-megapixel digital camera (Canon Inc., Japan). Photographs were processed and bacterial size was deter-mined using the AXIOVISION 4.1 software (Carl Zeiss) (Medeot et al 2010).…”