Pressure and Temperature Combined With Microbial Supernatant Effectively Inactivate Bacillus subtilis Spores.

Jingyu Li,Xiaosong Hu,Fang Chen,Li Dong,Yaxin Sun

doi:10.3389/fmicb.2021.642501

Abstract

Spores from the Bacillus species pose a challenge to the food industry because of their ubiquitous nature and extreme resistance. Accumulated evidence indicates that it is effective to induce spore germination homogenously before killing them. However, it is difficult to obtain and apply exogenous germination factors, which will affect food composition. Therefore, this study screened endogenous germinants from microorganisms by assessing the effect of Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae, Lactiplantibacillus plantarum, and Streptococcus thermophilus cultures (cell-free) on B. subtilis spore germination. The results showed that the supernatants from these five microorganisms induced spore germination instead of sediments. Moreover, the supernatants of E. coli, B. subtilis, and S. cerevisiae exhibited higher germination rates than L. plantarum and S. thermophilus, and the induction effects were concentration-dependent. Furthermore, plate counting confirmed that the microbial supernatants induced the lowest spore germination ratio on strains B. subtilis FB85 [germination receptors (GRs) mutant] but not strains B. subtilis PB705 (PrkC mutant). In addition, B. subtilis and S. cerevisiae supernatants, combined with pressure and temperature, were effective in spore inactivation. The findings suggested that microbial supernatants may include agents that induce spore germination and may be used for spore inactivation.

Highlights

The Bacillus species is a major concern in the food industry as its spores can trigger food spoilage and even food poisoning (Kochan et al, 2018; Ortiz et al, 2019)
The supernatants, filtered supernatants, solid and liquid bacterial precipitation after ultrasonic crushing from B. subtilis, E. coli, S. thermophilus, L. plantarum, and S. cerevisiae were prepared and exposed to 108 CFU/ml spores of B. subtilis strain 168 at 37°C
In the experiments with the treatment of supernatants, S. thermophilus and L. plantarum exhibited the same effect for dipicolinic acid (DPA) release of spores, which was better than the others, with a 30–40% ratio

Summary

Introduction

The Bacillus species is a major concern in the food industry as its spores can trigger food spoilage and even food poisoning (Kochan et al, 2018; Ortiz et al, 2019). The germination pathways of most spores have been mainly divided into two types: nutrient and non-nutrient germinants (Setlow et al, 2017). PGNs can interact with the PASTA (penicillin binding-associated and serine/threonine kinaseassociated) domain of PrkC kinase, and activated PrkC induces spore germination by delivering the signal to downstream proteins such as phosphorylating EF-G (Shah et al, 2008). Most of these germinants are not used in food processing because it is difficult to gain substances such as peptidoglycans in large amounts. It is of great significance to screen the germinants for inducing spore germination, and sterilize them to effectively control food spoilage

Methods

Results

Conclusion