Abstract
As alternatives to antibiotics in feed, probiotic Bacillus carries multiple advantages in animal production. Spores undergo strain-related germination in the gastrointestinal tract, but it is still unknown whether the probiotic function of the Bacillus depends on the germination of spores in vivo. In this study, based on 14 potential probiotic Bacillus strains from fermented food and feed, we detected the germination response of these Bacillus spores in relation to different germinating agents. The results showed the germination response was strain-specific and germinant-related, and nutrient germinant L-alanine significantly promoted the growth of strains with germination potential. Two strains of Bacillus subtilis, S-2 and 312, with or without a high spore germination response to L-alanine, were selected to study their morphological and genic differences induced by L-alanine through transmission electron microscopy and comparative transcriptomics analysis. Consequently, after L-alanine treatment, the gray phase was largely increased under microscopy, and the expression of the germination response genes was significantly up-regulated in the B. subtilis S-2 spores compared to the B. subtilis 312 spores (p < 0.05). The protective effect of L-alanine-induced spore germination of the two strains was comparatively investigated both in the IPEC-J2 cell model and a Sprague–Dawley (SD) rat model challenged by enterotoxigenic Escherichia coli K99. The result indicated that L-alanine helped B. subtilis S-2 spores, but not 312 spores, to decrease inflammatory factors (IL-6, IL-8, IL-1 β, TNF-α; p < 0.05) and promote the expression of occludin in IPEC-J2 cells. Besides, supplement with L-alanine-treated B. subtilis S-2 spores significantly improved the growth of the SD rats, alleviated histopathological GIT lesions, and improved the ratio of jejunal villus length to crypt depth in comparison to the B. subtilis S-2 spores alone (p < 0.05). Improved species diversity and abundance of fecal microbiota were only observed in the group with L-alanine-treated S-2 spores (p < 0.05). The study demonstrates L-alanine works well as a probiotic Bacillus adjuvant in improving intestinal health, and it also provides a solution for the practical and accurate regulation of their use as antibiotic alternatives in animal production.
Highlights
Antimicrobial resistance has been recognized as one of the top three major threats to public health by The World Health Organization (Xiong et al, 2018)
In the 14 Bacillus strains isolated for the potential sporeformer probiotics, plus the standard strain of B. subtilis 168, the result presented in Figures 1A–D showed that the germination response was strain-specific and germinant-related
L-alanine showed the potential to be a general germinating agent, which could induce the release of dipicolinic acid (DPA) and trigger the germination effect on most Bacillus spores
Summary
Antimicrobial resistance has been recognized as one of the top three major threats to public health by The World Health Organization (Xiong et al, 2018). Probiotics have been widely used in feed industries for preventing infections by alleviating antimicrobial-mediated resistance (Ouwehand et al, 2016; Mingmongkolchai and Panbangred, 2018; Abd El-Hack et al, 2020). As one of the general sources of probiotics, the spore-forming Bacillus species offer several advantages, such as heat stability and resistance to adverse environments of low pH and bile salt toxicity, in comparison to non-spore-formers (Davies, 2010; Setlow, 2010). Spore formation increases the survival of living cells during the manufacture and storage processes, including freezing, drying, thawing, and granulation. The Bacillus probiotics seemed to be more suitable for application in the feed industry because of their processing and storage stabilities and low production costs
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call