Abstract:

Cobalt （Co） is an important essential trace element for aquatic animals and is critical for maintaining their physiological and metabolic functions. Probiotics can convert inorganic cobalt into organic cobalt forms with less toxicity and higher bioavailability， providing dual benefits of cobalt and probiotics.Yeast R was screened to improve cobalt-enriched ability from the probiotics recommended by the European Union Qualification for the Safety of Microbial Strains （QPS）， which had high tolerance and enrichment capacity for cobalt chloride. The optimal cobalt enrichment conditions was determined as initial pH 5.5， incubation temperature 30 ℃， incubation time 76 h， and the addition of 1.5 g·L^-1 cobalt chloride for 4 h， resulting in total cobalt content of 3.78 g·kg^-1. Characterization tools confirmed the possible presence of spherical cobalt on the surface of cobalt-enriched yeast （R-Co） nanoparticles. In the zebrafish test， the addition of 0.166 7 mg·kg^-1 R-Co had no effect on growth performance and improved survival rate under ammonia-nitrogen stress and cold stress compared with the addition of 0.166 7 mg·kg^-1 inorganic cobalt， suggesting that yeast R is an efficient cobalt-enriched strain with the potential of replacing inorganic cobalt for promising applications in improving the health and resilience of aquatic animals.

Key words: probiotic yeast, trace element cobalt, characterization, zebrafish, stress resistance

摘要：

钴（Co）是水产动物的必需微量元素，对维持其生理和代谢功能至关重要，益生菌可以将无机钴转化为毒性更小、生物利用度更高的有机钴形式，为水产动物提供钴元素和益生菌的双重益处。从欧盟微生物菌种安全资格认证（Qualified Presumption of Safety，QPS）推荐的益生菌中筛选出对氯化钴具有高耐受性和高富集能力的酵母R并对其富钴能力进行提升。确定最佳富钴条件为初始pH 5.5、培养温度为30 ℃、培养时间为76 h、在培养4 h时添加1.5 g·L^-1氯化钴，总钴含量为3.78 g·kg^-1。表征手段证实了富钴酵母（R-Co）表面可能存在球形钴纳米粒子。在斑马鱼试验中，与添加0.166 7 mg·kg^-1的无机钴相比，0.166 7 mg·kg^-1的R-Co对其生长性能没有影响，并且在氨氮应激和冷胁迫下提高了斑马鱼存活率，表明酵母R是一种高效富钴菌株，具有替代无机钴的潜力在提高水产动物健康和抗逆性方面具有广阔的应用前景。

关键词: 益生酵母, 微量元素钴, 表征, 斑马鱼, 抗应激