PREVENTION OF PINK-PIGMENTED METHYLOTROPHIC BACTERIA (METHYLOBACTERIUM-MESOPHILICUM) CONTAMINATION OF PLANT-TISSUE CULTURES

Pink-pigmented facultative methylotrophic bacteria(PPFMs) have been fo und on the surfaces of leaves of most plants tested. We found PPFMs on the leaf surfaces of all 40 plants (38 species) tested and on soybean pods by pressing onto AMS medium with methanol as the sole carbon sou rce. The abundance ranged from 0.5 colony forming unit (cfu)/cm(2) to 69.4 cfu/cm(2) on the leaf surfaces. PPFMs were found in homogenized l eaf tissues of only 4 of the species after surface disinfestation with 1.05% sodium hypochlorite and were rarely found in cultures initiated from surface disinfested Datura innoxia leaves or inside surface disi nfested soybean pods. Of 20 antibiotics tested for PPFM growth inhibit ion, rifampicin was the most effective and of seven others which also inhibited PPFM growth, cefotaxime should be the most useful due to the expected low plant cell toxicity. These antibiotics could be used in concert with common surface sterilization procedures to prevent the in troduction or to eliminate PPFM bacteria in tissue cultures. Thus, whi le PPFMs are present on the surfaces of most plant tissues, surface di sinfestation alone can effectively remove them so that uncontaminated tissue cultures can be initiated in most cases.