Phenotypic, fermentation characterization, and resistance mechanism analysis of bacteriophage-resistant mutants of Lactobacillus delbrueckii ssp. bulgaricus isolated from traditional Chinese dairy products

Abstract

Bacteriophage infection is a large factor in dairy industrial production failure on the basis of pure inoculation fermentation, and developing good commercial starter cultures from wild dairy products and improving the environmental vigor of starter cultures by enhancing their phage resistance are still the most effective solutions. Here we used a spontaneous isolation method to obtain bacteriophage-resistant mutants of Lactobacillus delbrueckii ssp. bulgaricus strains that are used in traditional Chinese fermented dairy products. We analyzed their phenotypes, fermentation characteristics, and resistance mechanisms. The results showed that bacteriophage-insensitive mutants (BIM) BIM8 and BIM12 had high bacteriophage resistance while exhibiting fermentation and coagulation attributes that were as satisfying as those of their respective parent strains KLDS1.1016 and KLDS1.1028. According to the attachment receptor detection, mutants BIM8 and BIM12 exhibited reduced absorption to bacteriophage phiLdb compared with their respective bacteriophage-sensitive parent strains because of changes to the polysaccharides or teichoic acids connected to their peptidoglycan layer. Additionally, genes, including HSDR, HSDM, and HSDS, encoding 3 subunits of a type I restriction-modification system were identified in their respective parent strains. We also discovered that HSDR and HSDM were highly conserved but that HSDS was variable because it is responsible for the DNA specificity of the complex. The late lysis that occurred only in strain KLDS1.1016 and not in strain KLDS1.1028 suggests that the former and its mutant BIM8 also may have an activatable restriction-modification mechanism. We conclude that the L. bulgaricus BIM8 and BIM12 mutants have great potential in the dairy industry as starter cultures, and their phage-resistance mechanism was effective mainly due to the adsorption interference and restriction-modification system.

Beyond the A‐layer: adsorption of lipopolysaccharides and characterization of bacteriophage‐insensitive mutants of Aeromonas salmonicida subsp. salmonicida

“…Having an A‐layer anchored on the LPS did not seem to modify the gel migration pattern (Shaw et al , ). A BIM may lose its ability to resist a phage if it is no longer exposed to it, or if the bacterium is subcultured several times (Deng et al , ). As previously noted (Imbault et al , ), BIMs generated from the A‐layer positive strain did not retain the resistance phenotype over time.…”

“…In Lactobacillus delbrueckii subsp. bulgaricus , analysis of BIMs showed that the attachment and the adsorption of the phage to the bacterial receptor was a critical step, and that it was hindered by a change in the polysaccharide structure on their S‐layer (Deng et al , ). Other studies pointed to the presence of quorum‐sensing‐regulated phage defense mechanisms or changes in the gene sequence of the receptor (Hossain et al , ; Tan et al , ).…”

Characteristics of lytic phage vB_EcoM-ECP26 and reduction of shiga-toxin producing Escherichia coli on produce romaine

“…However, after 10 h of infection, resistance was observed despite vB_EcoM-ECP26 being a lytic phage. This phenomenon might be due to the emergence of bacteriophage insensitive mutants (BIMs) by methods such as the restriction-modification system or CRISPR-Cas immunity [15,39]. BIM also can induced by altering the LPS or cell envelope structures [41].…”

Phage Therapy: What Have We Learned?

“…The differential phage susceptibility determinants are exchangeable between strains of a given species. Bacteria can gain or lose sensitivity to a given phage or the ability to support this phage development by mutation-, recombination-, or horizontal gene transfer-driven changes in their phage susceptibility or phage defence determinants [ 151 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 , 172 , 173 , 174 , 175 ]. Several genes associated with phage resistance or susceptibility are carried by mobile genetic elements [ 120 , 158 , 175 , 176 , 177 , 178 , 179 , 180 , 181 , 182 , 183 , 184 , 185 , 186 , 187 ].…”