Characterization of an Epiphytic Bacterium Neptunomonas sp. BPy-1 on the Gametophytes of a Red Alga Pyropia yezoensis

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 greenshell mussels in New Zealand. Physiological tests revealed that 22 characters were identical between 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 concentration yielded two types of gametophytes, a compressed or callus-like form and a nearly normal 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.