Selection and characterization of a high-temperature tolerant strain of Porphyra haitanensis Chang et Zheng (Bangiales, Rhodophyta)

Abstract

Porphyra haitanensis is one of the most economical nutritive marine algae; however, its production and quality are significantly jeopardized by high temperatures. Selection of heat-resistant strains will greatly reduce the economic risks and benefit to the nori industry. Three previously isolated and improved strains with a high yield were screened at 28°C and identified, of which one strain, ZS-1, showed significantly improved heat tolerance. Upon further characterizing of the cultures of the ZS-1 strain and the wild-type (WT) strain at 28°C and 30°C, the ZS-1 conchospore germlings survived at rates of 69.9% and 59.6%, while the WT conchospore germlings survived at significantly lower rates of 15.9% and 6.7%, respectively, over a period of 15 days. Furthermore, ZS-1 conchospore germlings divided at significantly higher rates of 100% and 88.6% compared to the WT conchospore germlings with 90.4% and 63.8%, respectively. When the 35-day-old conchospore germlings were transferred from the optimal temperature of 24°C to higher temperatures of 28°C and 30°C, the ZS-1 blades sustained growth over a 25-day period without decay and increase of blade lengths with a factor of 18.5 and 10.3 times, respectively. The blade lengths of the WT germlings only increased by a factor of 1.7 and 0.9 times and began to decay after being cultured for 15 days at 28°C and 30°C. At 24, 28, and 30°C, the ZS-1 blades grew 3.4, 8.6, and 8.0 times faster than those of the WT. Evidently, ZS-1 is a fast-growing and heat-resistant strain compared to the WT strain and may offer an alternative for the nori industry.