Microbial Interactions & Microbial Ecology

Biography

Biography: Verena Hauke-Poinsot

Abstract

Nitrogen fixation results from a successful and complex interaction between bacteria (rhizobia) and a family of crops (legumes). This process is an endosymbiosis as the bacteria invade the root hairs and dedicated root organs: the nodules. One crucial signal to start this interaction is a family of lipochito oligosaccharides (LCO) called Nod factors (1). The variety of the backbone decorations and the length of the fatty chain are keys to the specific recognition of the host. The plant recognizes one precise design, allowing protecting itself from the invasion of pathogens. Their structure has been studied in detail in recent decades and encoding genes (almost located on a plasmid (pSym)) have been determined (2). However, the time-course of their biosynthesis is a recent discovery (2016). This could only be achieved by combining site-directed mutagenesis on a rhizobium model (here Sinorhizobium sp. IRBG) with highly specific and sensitive LC/MSMS analyses (MRM, EPI and EMS) of LCOs and COs. The last are chitooligomers without lipid chain, which are synthesis intermediates that could be analyzed in parallel to the Nod factors (3). These advances in analytical techniques provided a new point of view on the biosynthesis of LCOs. Actually, even if some decoration genes are in the same locus than the one encoding the skeleton and even some other genes encoding for sugar moieties are located  in distant loci, le sugar backbone is synthesized completely first and decorated later.