Effect of Probiotics on Juvenile Tachypleus tridentatus Gut Microbiota

The population of tri-spine horseshoe crabs (HSCs) Tachypleus tridentatus has sharply decreased in recent decades. Domestication and manual releasing are now used to recover it. In order to accelerate the growth of T. tridentatus in indoor environment, in this study, gut microbiota of 2nd instar T. tridentatus was supposed to be improved by putting probiotics in water environment and thus promoted the health and growth of the host. Using 16S rRNA sequencing of gut samples, we examined the intestinal microbiome of juvenile HSCs and studied the effect of probiotics. Results showed that there was no significant difference between groups fed with high and low concentrations (1 × 10⁷, 1 × 10¹² CFU mL⁻¹) of Bacillus subtilis and high concentration (1 × 10¹² CFU mL⁻¹) of Lactobacillus, and no significant difference compared with the control group, but the diversity of Lactobacillus group with low concentration (1 × 10⁷ CFU mL⁻¹) was significantly higher than those of other groups. Microbial-mediated functions predicted by PICRUSt showed that ‘Cellular Processes’, ‘Metabolism’ and ‘Organismal Systems’ pathways significantly increased in groups of Bacillus subtilis and Lactobacillus group with low concentration. The results showed that two types of probiotics with different concentrations have other effects on the structure, richness and function of intestinal microbes. By searching the literature and conducting pre-experiments, we forecasted the short time of breeding under the probiotic environment may not have much effect. The present study for the first time investigated the impact of probiotics on gut microbiota of juvenile HSCs and found them may benefit for the growth and health of HSCs.