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Distribution, Enumeration, and Identification of Nitrogen-Fixing Bacteria Associated with Decay in Living White Fir Trees. Paul E. Aho, Plant Pathologist, Forestry Sciences Laboratory, Pacific Northwest Forest and Range Experiment Station, Forest Service, USDA, Corvallis, Oregon 97331; Ramon J. Seidler(2), Harold J. Evans(3), and P. N. Raju(4). (2)Department of Microbiology, Oregon State University, Corvallis 97331; (3)Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; (4)Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, Present address: Botany Department, University of Madras, Madras, India. Phytopathology 64:1413-1420. Accepted for publication 3 June 1974. DOI: 10.1094/Phyto-64-1413.

Of 130 fermentative, gram-negative bacterial isolates from the major decays in white fir trees, 68 were shown to be capable of fixing atmospheric nitrogen as determined by the acetylene reduction technique. Five isolates were also tested quantitatively by use of ¹⁵N₂. The N₂-fixing bacteria were isolated from 31 trees in 16 widely scattered locations and were associated with all decay stages caused by the most important fungal associations in white fir heartwood. High populations (10⁵ to 10⁶ cells/ml expressed sap) of these important bacteria were associated with the early and incipient decay stages caused by Hericium abietis and Phellinus chrysoloma, but not with Echinodontium tinctorium. The bacteria were characterized and identified as Enterobacter agglomerans, E. aerogenes, Klebsiella pneumoniae, and other atypical Enterobacter sp. This is the first report of N₂ fixation by the species E. agglomerans.