Rhizobium Gum: A Novel Cosmetic Ingredient from Soil to the Skin

Whereas many products used by cosmetic customers come from natural molecules extracted and purified from various sources, most of them are modified by technical steps in order to give new functionalities. An example of this is rhizobium gum, a new polysaccharidea produced by fermentation of a Rhizobium sp strain. It is a typical example of what technology can design to create new properties and new applications from a “basic” natural ingredient. In this article, we look at its origin, evolution and properties.

The soil is a complex biotope with many interactions occurring between plants and microorganisms. These interactions, such as symbiotism, commensalism or parasitism, are based on evolution and the necessity for each microorganism to position itself in the alimentary chain.

Our study focuses on a symbiotic interaction between a bacterium and a plant that is advantageous for both parts. For instance, rhizobium strains are well known to transform the inorganic nitrogen (gas) from the atmosphere into nitrogen usable by the plant (ions); and to counterbalance, the bacteria use the organic molecules synthesized by plants and released near the roots to grow and to maintain their metabolism.

The strength of microorganisms such as bacteria is the diversity and various skills of their species. During a screening program, in collaboration with the Centre National de la Recherche Scientifique (CNRS) – the National Council for Scientific Research – a new strain of rhizobium bacteria was isolated. Identified as a Rhizobium sp., this new species demonstrates the ability to produce a polymer near the roots of sunflowers.

In soil, during dry conditions or drought, this strain synthesizes the polymer in order to modify the structure of the soil near the roots of the sunflower to enhance the aggregation of root-adhering soil. The bacteria create a thin layer of polymer in contact with the roots system (Figure 1). This polymer maintains a high water supply near the roots that is usable by the plant in severe drought. The strain finds nutrients near the roots resulting from the roots system leaking metabolites. Thus, a symbiotic relationship exists between the plant and the bacteria: the polymer keeps the moisture near the roots of the plant and the bacteria uses nutrients lost by the plant.

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