Mechanism for Utilization of the Populus-Derived Metabolite Salicin by a Pseudomonas—Rahnella Co-Culture

Abstract

Pseudomonas fluorescens GM16 associates with Populus, a model plant in biofuel production. Populus releases abundant phenolic glycosides such as salicin, but P. fluorescens GM16 cannot utilize salicin, whereas Pseudomonas strains are known to utilize compounds similar to the aglycone moiety of salicin–salicyl alcohol. We propose that the association of Pseudomonas to Populus is mediated by another organism (such as Rahnella aquatilis OV744) that degrades the glucosyl group of salicin. In this study, we demonstrate that in the Rahnella–Pseudomonas salicin co-culture model, Rahnella grows by degrading salicin to glucose 6-phosphate and salicyl alcohol which is secreted out and is subsequently utilized by P. fluorescens GM16 for its growth. Using various quantitative approaches, we elucidate the individual pathways for salicin and salicyl alcohol metabolism present in Rahnella and Pseudomonas, respectively. Furthermore, we were able to establish that the salicyl alcohol cross-feeding interaction between the two strains on salicin medium is carried out through the combination of their respective individual pathways. The research presents one of the potential advantages of salicyl alcohol release by strains such as Rahnella, and how phenolic glycosides could be involved in attracting multiple types of bacteria into the Populus microbiome.

Catabolic pathway acquisition by soil pseudomonads readily enables growth with salicyl alcohol but does not affect colonization ofPopulusroots

“…Eight of the isolates grew in M9 minimal medium with SA as the sole source of carbon and energy, including the previously-characterized Pseudomonas sp. GM16 (hereafter ‘GM16’) [25]. One strain, Pseudomonas sp.…”

“…Poplar trees exude large quantities of phenolic compounds derived from salicyl alcohol (SA), including salicin, populin, and tremuloidin [23]. These compounds are thought to act primarily as inhibitors of herbivory [24] but also serve as potential carbon sources for soil microbes [25]. An intermediate in the SA catabolic pathway, salicylic acid is a major component of plant exudates and thought to influence microbiome community composition [26].…”