Cryotolerance of Lactobacillus delbrueckii subsp. bulgaricus CFL1 is modified by acquisition of antibiotic resistance

This study aimed to relate the acquisition of different antibiotic resistances and the corresponding physiological responses to cold stress of Lactobacillus delbrueckii subsp. bulgaricus strain CFL1. Six resistant mutants were spontaneously obtained and studied depending on the target of the antibiotic: (i) bacitracin and vancomycin (BacR, VanR, wall synthesis), (ii) novobiocin (NovR, DNA replication), and (iii) kanamycin, spiramycin, streptomycin (KanR, SpiR, StrR, RNA translation). The mutations modified the growth and the cold stress response at three different physiological levels: (i) VanR and SpiR mutants showed significant lower growth rates compared to the wild type strain. (ii) VanR and BacR mutants displayed a slightly higher resistance to a freezing-thawing challenge whereas StrR and SpiR mutants were more sensitive compared to the wild type. (iii) The recovery of acidification activity after freezing and during frozen storage was improved by considering the NovR strain, but not with the VanR and SpiR mutants. Thus, acquisition of some antibiotic resistance by spontaneous mutation led to modification of the cold stress response. The hypothesis of a unique cellular thermostat is discussed regarding the diversity of the tested antibiotics.