Abstract: To explain the effect of Bacillus spp. on the growth and physiology of Pyropia yezoensis, Pyropia yezoensis fronds and one of its epiphytic bacteria-Bacillus sp. LPyS1 were used as materials. Effects of the different time points (0, 6, 12, 24, 48, 72 h), the relative growth rate (RGR), the activity of superoxide dismutase (SOD), peroxidase (POD), phycobiliprotein(Chla), photosynthetic pigments (RPE，RPC and APC), total protein（TP）, malondialdehyde (MDA) and free proline (Pro) content were studied. The results showed that, compared with the control group, Bacillus could significantly increase the RGR of Pyropia yezoensis in a short period of time (P<0.05), Bacillus had no significant effect on the activity of SOD, POD and the content of malondialdehyde (MDA) in Pyropia yezoensis fronds (P>0.05). After 24 h of culture, the co-culture group and control group Pyropia yezoensis produced excessive osmotic adjustment substances. The total protein, photosynthetic pigment and phycobiliprotein of co-culture group were significantly higher than that of the control group at 48 h (P<0.05), but the content of Pro in the co-culture group was significantly lower than that in the control group at 48 h(P<0.01). This experimental study showed Bacillus sp. LPyS1 was beneficial to promote the growth of Pyropia yezoensis. Therefore, it is speculated that this algal epiphytic bacteria might provide nutrients for Pyropia yezoensis in the algal environment, thereby affecting the growth and physiological state of Pyropia yezoensis.

Key words: Pyropia yezoensis, Bacillus sp.LPyS1, phccosphere, growth, physiological