The use of Racomitrium japonicum, a drought resistant bryophyte used for roof-greening, is gradually increasing. However, its utilization is hampered by slow growth rate. Here we isolated culturable bacteria from hydroponic cultivation samples to identify isolates that could promote moss growth. Most of the isolates belonged to Pseudomonas, Rhodococcus, and Duganella species. The isolates were biochemically characterized according to their type of interaction with plants, i.e., production of auxin, siderophores, or hydrogen cyanate, growth in the absence of an added nitrogen source, calcium phosphate solubilization, utilization of sugars, polymers, or aliphatic compounds, and antifungal activity. The isolates were applied to sterile protonemata and non-sterile adult gametophytes of R japonicum to evaluate their effect on plant growth. Furthermore, we isolated fungi that inhibited moss growth. Our results suggest that the microbial community structure in hydroponic cultures is important to stabilize moss production and the isolates that promote moss growth have potential to be utilized as biofertilizers for moss production. (C) 2011, The Society for Biotechnology, Japan. All rights reserved.