Under UV-B stress, the MAAs exhibited efficient protection on Escherichia coli cells ( Fig. 7). The photoprotection or survival rate of E. coli cells was 26.0, 29.8, 38.8 and 59.7% at 1.38, 2.77, 5.55 and 11.1 mg mL−1 MAAs, respectively. No significant negative effect of MAAs was found on the growth of E. coli cells at the same concentration of MAAs as mentioned above ( Fig. 7); however, the growth was greatly affected under UV-B radiation and survival rate of E. coli cells was only 14.8% after above-mentioned period of UV-B irradiation.