NITROGEN-FIXATION IN A BIOTYPE OF ERWINIA-HERBICOLA RESEMBLING ESCHERICHIA-COLI

Two nitrogen‐fixing members of the Enterobacteriaceae have been isolated from paper mill process water and compost. Although they closely resembled Escherichia coli, detailed biochemical characterization of these and 7 other isolates established that they should be assigned to a biotype of Erwinia herbicola. They may be distinguished from E. coli by their lack of amino acid decarboxylase activity, their ability to utilize cellobiose and malonate and to ferment cellobiose and amygdalin. In one of them, the capacity to fix nitrogen, ferment cellobiose and utilize malonate was resistant to the effects of ethidium bromide, acridine orange and sodium dodecyl sulphate, and the ability to utilize cellobiose could not be transferred on to E. coli or Salmonella typhi. It is therefore concluded that these characters are not carried on transferable plasmids. Forty‐eight strains of E. coli of varying origin were examined for acetylene reducing activity and all were found to be negative. It is concluded that hitherto no naturally occurring strains of E. coli have been shown to fix nitrogen. Copyright © 1979, Wiley Blackwell. All rights reserved