The zone immediately surrounding the actively growing region of a plant root. Typically 1–2 mm thick, it consists of a biofilm of water and soluble substances derived from the plant, soil constituents, and a community of fungi, bacteria, and other microorganisms that interact with each other and with the plant. The rhizosphere has a profound influence on the growth and survival of the plant, notably in helping it to absorb nutrients from the soil and inhibiting root pathogens, and on soil composition and structure. The root releases or actively secretes a wide range of soluble substances, including amino acids, proteins, sugars, polysaccharides, and vitamins, as well as the layer of slime (mucigel) that helps to protect and lubricate the growing root tip. These substances attract, and are exploited as food by, microflora (fungi, bacteria, etc.) and microfauna (e.g. nematodes, mites, and snails), which together form a complex community in the rhizosphere. Some microorganisms are beneficial to the plant, for example by mineralizing soil nutrients to make them available to the plant or by producing vitamins, antibiotics, or signal molecules that encourage plant growth. Also, conditions in the rhizosphere encourage the germination of spores of fungi that form mutualistic mycorrhizas with plant roots; in some cases the rhizospere can inhibit the growth of competing plant species. The community of organisms found in any particular rhizosphere can be characterized by direct analysis of their genetic material derived from a suitable sample, using the techniques of metagenomics.