Genome Characteristics of Frankia sp. Reflect Host Range and Host Plant Biogeography

At present, there are six published genomes of the actinobacterium Frankia with six more at various stages of completion and several more are being planned. These genomes cover the four known phylogenetic clusters and range in size from five to ten Mb. The strains studied have different symbiotic status ranging from obligate symbionts to non-symbiotic or defective saprotrophs with several shades of facultative symbionts. There is no genetic transformation system for any frankiae and thus the symbiotic determinants are not yet known with certainty. However, the genomes have helped discern evolutionary tendencies as they relate to symbiosis