Species of bacterium
Bradyrhizobium japonicum is a species of legume-root nodulating, microsymbiotic nitrogen-fixing bacteria. The species is one of many Gram-negative, rod-shaped bacteria commonly referred to as rhizobia.[citation needed] Within that broad classification, which has three groups, taxonomy studies using DNA sequencing indicate that B. japonicum belongs within homology group II.[2]
Uses
Agriculture
B. japonicum is added to legume seed to improve crop yields,[3] particularly in areas where the bacterium is not native (e.g. Arkansas soils).[4] Often the inoculate is adhered to the seeds prior to planting using a sugar solution.[5]
Research
A strain of B. japonicum, USDA110, has been in use as a model organism since 1957.[citation needed] It is widely used to study molecular genetics, plant physiology, and plant ecology due to its relatively superior symbiotic nitrogen-fixation activity with soybean (i.e. compared to other rhizobia species). Its entire genome was sequenced in 2002, revealing that the species has a single circular chromosome with 9,105,828 base pairs.[6]
Metabolism
B. japonicum is able to degrade catechin with formation of phloroglucinol carboxylic acid, further decarboxylated to phloroglucinol, which is dehydroxylated to resorcinol and hydroxyquinol.[citation needed]
B. japonicum possess the nosRZDFYLX gene, which aides in denitrification and has two catalytic subunits - Cu-a and Cu-z (with several histidine residues). It manages an expression cascade that can sense oxygen gradients, termed 'FixJ-FixK2-FixK1.' FixJ positively regulates FixK2, which activates nitrogen respiration genes, as well as FixK1. FixK1 mutants are unable to respire from nitrogen due to a defective catatylic copper subunit (Cu-z) in nosRZDFYLX.[7]
