American Journal of Plant Sciences, 2014, 5, 3652-3661 Published Online November 2014 in SciRes. http://www.scirp.org/journal/ajps http://dx.doi.org/10.4236/ajps.2014.524381 How to cite this paper: Handayani, M., Sasaki, H., Matsuda, R., Takechi, K., Takano, H. and Takio, S. (2014) Characterization of an Epiphytic Bacterium Neptunomonas sp. BPy-1 on the Gametophytes of a Red Alga Pyropia yezoensis. American Jour- nal of Plant Sciences, 5, 3652-3661. http://dx.doi.org/10.4236/ajps.2014.524381 Characterization of an Epiphytic Bacterium Neptunomonas sp. BPy-1 on the Gametophytes of a Red Alga Pyropia yezoensis Midia Handayani 1 , Hiroyuki Sasaki 1 , Ryuya Matsuda 1 , Katsuaki Takechi 1 , Hiroyoshi Takano 1 , Susumu Takio 1,2 1 Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan 2 Center for Marine Environment Studies, Kumamoto University, Kumamoto, Japan Email: stakio@gpo.kumamoto-u.ac.jp Received 3 October 2014; revised 2 November 2014; accepted 16 November 2014 Copyright © 2014 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract The established culture of gametophytes of the red alga Pyropia yezoensis (TU-1) is superficially colonized by epiphytic bacteria. By 16S rRNA sequencing, 6 bacterial species were identified, and a culturable bacterium, Neptunomonas sp. BPy-1, was isolated. The 16S rRNA sequences of BPy-1 showed 100% identity with that of Neptunomonas sp. 0536, a probiotic bacterium found in green- shell mussels in New Zealand. Physiological tests revealed that 22 characters were identical be- tween BPy-1 and 0536, but that 4 characters differed. BPy-1 cannot grow in the artificial seawater used for the culture of gametophytes. BPy-1 can grow in the artificial seawater with ethanol or butanol but not in methanol or propanol. To determine the effect of BPy-1 on gametophyte growth, BPy-1 colonization was reduced by 80% using a multi-enzyme cleaner. Changing the cleaner con- centration yielded two types of gametophytes, a compressed or callus-like form and a nearly nor- mal form. BPy-1 promoted the growth of the treated gametophytes with relatively normal form, while it showed less effect on compressed gametophytes. These findings suggested that BPy-1 promotes the growth of damaged gametophytes but does not affect the development of normal gametophytes. Keywords Neptunomonas, Pyropia yezoensis, Ethanol-Eating Bacteria, Epiphytic Bacteria