High population of Sphingomonas species on plant surface


Hongik Kim, Department of Applied Biological Chemistry, Graduate School of Agriculture & Agricultural Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (e-mail: aa67039@hongo.ecc.u-tokyo.ac.jp).


A unique microbial community exists on upper leaf surfaces because strong irradiation by the sun restricts and selects growing micro-organisms. The micro-organisms on plant aerial parts are possibly able to control plant pathogens and to promote plant growth as do some of the micro-organisms on plant roots. Sphingomonas species on plant tissues (seed, leaf and flower) were detected and enumerated by the amplification of a specific part of the small subunit rRNA gene. Sphingomonads were found on 26 plant species belonging to 11 families. The maximum population number of Sphingomonas was 108 g−1 (wet weight) plant tissue. The maximum population ratio of Sphingomonas to the total aerobic bacteria was 58% when it was counted on glucose-nutrient agar plates. Consistent differences in population number and population ratio were not found among seeds, leaves and flowers. The role of sphingomonads on plant aerial parts is discussed.