Screening of marine Streptomyces spp. for potential use as probiotics in aquaculture

Marine Streptomyces strains (CLS-28, CLS-39 and CLS-45) were used to colonise Artemia nauplii (Instar I) and 15 d old adult Artemia prior to challenge with Vibrio harveyi and V. proteolyticus. The LC50 of V. harveyi and V. proteolyticus was found to be ∼ 106 CFU ml− 1. V. proteolyticus was more pathogenic than V. harveyi at 106 CFU ml− 1. A significant reduction in mortality (P < 0.001) was found by addition of 1% wet cell mass of Streptomyces strains in nauplii and adult Artemia against both the pathogens. The best protective responses were shown by CLS-39 in both nauplii and adults against V. harveyi and by CLS-39 in nauplii and CLS-28 in adults against V. proteolyticus. Shrimp feeds were supplemented with Streptomyces cell mass at 1% dosage and fed to black tiger shrimp Penaeus monodon postlarvae for 15 d in three treatments with two treatments of commercial probiotic (T1: feed + CLS-28; T2: feed + CLS-39; T3: feed + CLS-45; T4: feed + Sanolife® commercial probiotic and T5: Sanolife® commercial probiotic in water). During this time, ammonia was in the range of 1 to 2 ppm in all the treatments with significant differences between treatments (P < 0.05). Significant differences (P < 0.05) were also found in survival, total length and wet weight of the shrimp postlarvae during the 15 d trial. T5 showed the best gains in terms of length and weight followed by T1, T2, T3 and T4. Streptomyces treatments T1, T2 and T3 showed better survival and higher length and weight than the control and T4. Total heterotrophic bacteria and Vibrio counts were in the range of 108 and 106 CFU ml− 1 respectively in all the treatments. The Vibrio population differed significantly in the treatments (P < 0.05) and the total bacterial counts showed no significant differences in the treatments (P > 0.05). After challenge with V. harveyi at 107 CFU ml− 1, highest survival was found in T1 and T5. Among the Streptomyces treatments, T1 showed significantly higher survival compared to the control, followed by T2 and T3. Thus Streptomyces strains show promise as probiotic agents in mariculture.