This study was designed to describe a series of in vitro tests that may aid the discovery of probiotic strains from actinomycetes. Actinomycetes were isolated from marine sediments using four different isolation media, followed by antimicrobial activity and toxicity assessment by the agar diffusion method and the hemolysis of human blood cells, respectively. Extracellular enzymatic production was monitored by the hydrolysis of proteins, lipids and carbohydrates. Tolerance to different pH values and salt concentrations was also determined, followed by hydrophobicity analysis and genetic identification of the most promising strains. Five out of 31 isolated strains showed antimicrobial activity against three Vibrio species. Three non-hemolytic strains (N7, RL8 and V4) among these active isolates yielded positive results in hydrophobicity tests and exhibited good growth at salt concentrations ranging from 0% to 10%, except strain RL8, which required a salt concentration >0.6%. Although these strains did not grow at pH<3, they showed different enzymatic activities. Phylogenetic analysis revealed that strains N7 and V4 have more than 99% identity with several Streptomyces species, whereas the closest matches to strain RL8 are Streptomyces panacagri and Streptomyces flocculus, with 98% and 98.2% similarity, respectively. Three actinomycetes strains showing probiotic-like properties were discovered using several in vitro tests that can be easily implemented in different institutions around the world.

Growth in shrimp farming has shown an expansion of rearing farms and intensification of production methods, which have affected shrimp health, growth and survival and environmental integrity of the coastal areas, making the long-term viability of this farming industry doubtful. This industry demands alternative strategies to improve shrimp production, enhance disease resistance and take good care of the environment. Yeasts (live cell, total cell, or their active by-products) confer a benefit to the host by providing nutrition and protection against pathogens. This review summarizes the current knowledge of yeast species on: (i) shrimp aquaculture; (ii) shrimp nutrition; (iii) shrimp immunity; (iv) water and environment. Yeasts are used as alternative feed ingredients in aquaculture because of their nutritional value. Some products, such as b-glucans, chitin, nucleic acids, mannan oligosaccharides, b-carotene, B-complex, torulene, and torularhodin have been used in shrimp diets, showing direct effect on shrimp growth. Amylases, chitinases, phytases, and proteases are used to enhance gut maturity and digestive enzyme activity in shrimp larvae. The immune and antioxidant proprieties of yeasts have an important role as probiotics and immunostimulants to enhance shrimp resistance against common viral and bacterial diseases. Yeast bioactive products, such as glucans, nucleotides, polysaccharides, carotenoid pigments, lipids, proteins, and vitamins, activate the immune response directly or improve intestinal microbiota, specially glucans, which enhance shrimp circulating hemocytes (THC), phagocytosis, encapsulation, ProPO activity and melanization. Different yeast species, such as Debaryomyces sp., Candida sp., Rhodosporidium sp., Saccharomyces sp., and Yarrowia sp. have recently gained popularity as beneficial candidates in farmed organisms to maintain health conditions and well-being of different aquatic animals, including rearing shrimp. In addition, this study condensed current knowledge of the ability of yeasts to sustain the performance of marine shrimp and provide information for future research and development of yeast application in aquaculture.