PCR Analysis of expR Gene Regulating Biosynthesis of Exopolysaccharides in Sinorhizobium meliloti

Exopolysaccharide (EPS) production by the rhizobacterium Sinorhizobium meliloti is essential for root nodule formation on its legume host (alfalfa), and for establishment of a nitrogen‐fixing symbiosis between the two partners. Production of EPS II (galactoglucan) by certain S. meliloti strains results in a mucoid colony phenotype. Other strains that are unable to produce EPS II display a dry phenotype, due to the presence of an insertion element in the gene expR, a key regulator involved in many important cellular processes, including production of low‐molecular‐weight EPS II. We describe a series of three programmed undergraduate biochemistry laboratory classes teaching PCR and electrophoresis procedures to detect non‐functional expR loci in S. meliloti.