title: Evaluation of environmental bacterial communities as a factor affecting the growth of duckweedLemna minor.
abstract: BACKGROUND
  Duckweed (familyLemnaceae) has recently been recognized as an ideal biomass feedstock for biofuel production due to its rapid growth and high starch content, which inspired interest in improving their productivity. Since microbes that co-exist with plants are known to have significant effects on their growth according to the previous studies for terrestrial plants, this study has attempted to understand the plant-microbial interactions of a duckweed,Lemna minor, focusing on the growth promotion/inhibition effects so as to assess the possibility of accelerated duckweed production by modifying co-existing bacterial community.
  
  
  RESULTS
  Co-cultivation of asepticL. minorand bacterial communities collected from various aquatic environments resulted in changes in duckweed growth ranging from -24 to +14% compared to aseptic control. A number of bacterial strains were isolated from both growth-promoting and growth-inhibitory communities, and examined for their co-existing effects on duckweed growth. Irrespective of the source, each strain showed promotive, inhibitory, or neutral effects when individually co-cultured withL. minor. To further analyze the interactions among these bacterial strains in a community, binary combinations of promotive and inhibitory strains were co-cultured with asepticL. minor, resulting in that combinations of promotive-promotive or inhibitory-inhibitory strains generally showed effects similar to those of individual strains. However, combinations of promotive-inhibitory strains tended to show inhibitory effects while onlyAquitalea magnusoniiH3 exerted its plant growth-promoting effect in all combinations tested.
  
  
  CONCLUSIONS
  Significant change in biomass production was observed when duckweed was co-cultivated with environmental bacterial communities. Promotive, neutral, and inhibitory bacteria in the community would synergistically determine the effects. The results indicate the possibility of improving duckweed biomass production via regulation of co-existing bacterial communities.
authors.affiliation: Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871 Japan.
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Ishizawa
authors.affiliation: Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871 Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Kuroda
authors.affiliation: Division of Biosphere Science, Graduate School of Environmental Science, Hokkaido University, N10-W5, Kita-ku, Sapporo, 060-0810 Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Morikawa
authors.affiliation: Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871 Japan.
authors.forename: Michihiko
authors.initials: M
authors.lastname: Ike
keywords: Biomass production; Duckweed; Plant growth-inhibiting bacteria; Plant growth-promoting bacteria