Culture of low density E. coli cells in alginate–chitosan microcapsules facilitates stress resistance by up-regulating luxS/AI-2 system

• Cells in ELDCwc group have superior stress resistant ability to dEHDC group.
• Stress resistance of encapsulated bacteria was explained in quorum sensing aspect.
• The luxS deficient E. coli strain possessed weaker stress resistance in microcapsules.

Entrapped low density cells with culture (ELDCwc) have been proved as a more effective way than direct entrapped high density cells (dEHDC) and free cells to protect probiotics from harsh environment, that is, to improve their stress resistance. The aim of this study was to investigate whether bacterial quorum sensing (QS) facilitated the stress resistance of Escherichia coli in microcapsules by detecting the expression of luxS/AI-2 system. As a result, both the expression of luxS gene and the concentration of autoinducer-2 (AI-2, QS signal molecule) have been discovered higher in ELDCwc than in dEHDC and free cells. Besides that, the luxS mutant E. coli strain was used as a negative control of QS to verify the influence of QS on bacterial stress resistance in microcapsules. The significantly decreased viability of luxS mutant strain in simulated gastric fluid also indicated that the QS played a critical role in protecting microorganisms from severe environment.