Studies of growth and morphology of Frankia strains EAN1pec, EuI1c, CpI1, and ACN1AG

Abstract

A study was made of the ability of four strains of Frankia, representing two distinct host-compatibility groups, to utilize various carbon sources for growth. Isolates EAN1pec and EuI1c, representatives of host-compatibility group II, utilized a variety of sugars and sugar alcohols as carbon sources. Isolates CpI1 and ACN1AG, members of host-compatibility group I, did not use these substrates for growth. All of the isolates studied except for EAN1pec utilized propionate for growth. The only one of the four isolates unable to grow on dicarboxylic acids was EuI1c. Vesicles were detected microscopically during growth of EAN1pec and ACN1AG in media containing ammonia. The numbers and size of vesicles, however, were greater in media without ammonia. Strain ACN1AG did not form vesicles in any of the media when incubated at temperatures greater than 33 °C. The CpI1 isolate formed vesicles only when grown in ammoniafree media. Vesicles were not formed by strain EuI1c in any of the media. Sporulation of the four isolates was carbon-source dependent. Isolate CpI1 formed sporangia when grown in propionate-containing medium at 20 °C but formed none in the medium at 33 °C.