Yeast Lactose Agar

Principle And Interpretation

Symbiotic nitrogen fixation is accomplished by bacteria of the genus Rhizobium in association with legumes (plants that bear seeds in pods). These bacteria infect the root system of the legumes and further invade the host plant cells via an infection thread. Some of the cells of the plant are thus infected causing cell enlargement and an increased rate of cell division, leading to the formation of abnormal growth (nodules) on the root system. The legume, the bacteria and the nodule together constitute the nitrogen fixing system. The bacteria make nitrogen available to the plant, and in turn the bacteria derive nutrients from the tissues of the plant (1). Yeast Lactose Agar (2) is used for cultivation of soil microorganisms such as Rhizobium species (3).

Yeast extract serves as a good source of readily available amino acids, including vitamin B complex and accessory growth factors. It also poises the oxidation-reduction potential of medium in the range favourable for Rhizobia and serves as hydrogen donor in respiratory process (4). Lactose is the fermentable carbohydrate source. Magnesium provides cations essential for the growth of Rhizobia.