Identification of Tex and the Phage Shock Protein YthA as putative FtsH substrates associated with the cell envelope stress response in Lactococcus cremoris.

As part of the Cell Envelope Stress (CES) response orchestrated by the two-component system CesSR in lactococci, the FtsH protease is expected to play a role in counteracting stress, as observed in other bacteria. However, neither its specific role nor its substrates have been identified in this genus. The primary objective of this study was therefore to elucidate the FtsH function in the context of CES. A Lactococcus cremoris NZ9000 ΔftsH exhibited an extended lag phase, increased salt and heat sensitivity and lysozyme resistance. However, only the salt and heat sensitive phenotype could be restored by complementation of the ftsH deletion. Whole-genome sequencing revealed putative compensatory mutations in ΔftsH, including genes encoding a transcriptional regulator and components of ABC transporters. Although awaiting experimental validation, these mutations may nevertheless underscore the broader physiological significance of FtsH in L. cremoris. Furthermore, a comparative proteomic analysis of L. cremoris NZ9000 ΔftsH under CES conditions identified putative FtsH substrates. In vivo degradation experiments demonstrated an extended half-life of the RNA-binding protein Tex and the Phage-Shock Protein YthA in a growth-phase dependent manner, thereby proposing these proteins as putative FtsH substrates in L. cremoris. While the specific function of Tex remains to be elucidated, the regulated degradation of YthA suggests that proteolysis may represent an additional regulatory layer within the lactococcal CES response.