Professor, Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan

Biograph
M. Morikawa is a Professor of Environmental Molecular Biology at Faculty of Environmental Earth Science, Hokkaido University. He also serves as a vice president of the Japan Society for Environmental Biotechnology. His interest is in environmental microbiology. He obtained his doctoral degree from Graduate School of Engineering, Osaka University in 1994. Currently, he is one of the project leaders of Advanced Low Carbon Technology Research and Development Program, Japan Science and Technology Agency (JST-ALCA), under the project title of “Effective Aquatic Biomass Production Utilizing Mutualistic Microorganisms.” He has published more than 120 research articles and total times cited are 3,246 (Mar, 2019).

Speech Title: Axenic duckweed, a useful platform to study the holobiont plant

Abstract: Every plant harbors complex indogeneous and exogneous microbial communities that hold positive or negative symbiotic relationships. Bacteria that promote plant growth and health are called plant growth-promoting bacteria, PGPB, while those inhibit the growth are plant growth-inhibiting bacteria, PGIB (Ishizawa et al. 2019). Designing and stabilizing the microbial community structure with dominant PGPB and recessive PGIB population would be an ultimate biotechnology of nature-friendly and cost competitive industrial production of plant biomass. Compared with the soil environment, the microorganisms in the aquatic environments that associate to the plants are necessary to adhere and colonize on the plant bodies so that they may not be drained off by continuously running water. Quick adhesion and stable colonization are expected to be important traits of aquatic PGPB except for endophytes. Acinetobacter calcoaceticus P23 is one of the first duckweed PGPB described in the literature (Yamaga et al. 2010). P23 adheres and colonizes not only on the surface of plants but also to the plastic surfaces, excelling in the ability to form beneficial biofilm. P23 also has ability to increase the chlorophyll content in lettuce, a dicotyledon, as well as of a monocotyledon plant, duckweed (Suzuki et al. 2014).

We obtained a series of surface-colonizing PGPB for common duckweed, Lemna minor that widely distributes in freshwater areas and is one of the representative species in the genus Lemna. Aseptic L. minor was submerged short time in the water of the original pond. This method enabled us to select bacteria that can potentially establish symbiosis with L. minor at an early stage. It was found that seven out of eight of the early colonizing bacteria are PGPB, beneficial symbionts. Second, we constructed a triple symbiosis by intermixing the most competent PGPB Pseudomonas fulva Ps6 and A. calcoaceticus P23 on the host plant L. minor. This made it possible to evaluate the cooperation and competition quantitatively between the member bacteria. Because the duckweed is a fastest growing vascular plant that are easy to prepare aseptic and axenic plant, duckweed/bacteria co-culture system will be a potential platform for studying multiple way interaction among the host plant and its associated bacteria (Yamakawa et al. 2018).

References:
Yamaga et al. (2010) Envion. Sci. Technol. 44(16): 6470-6474
Suzuki et al. (2014) J. Biosci. Bioeng. 118(1): 41-44
Yamakawa et al. (2018) Plant Growth Regul. 86(2): 287-296
Ishizawa et al. (2019) Microb. Ecol. 77(2): 440-445