d-Methionine and d-Phenylalanine Improve Lactococcus lactis F44 Acid Resistance and Nisin Yield by Governing Cell Wall Remodeling

Hao Wu; Ershu Xue; Ning Zhi; Qianqian Song; Kairen Tian; Qinggele Caiyin; Lin Yuan; Jianjun Qiao

doi:10.1128/AEM.02981-19

d-Methionine and d-Phenylalanine Improve Lactococcus lactis F44 Acid Resistance and Nisin Yield by Governing Cell Wall Remodeling

Appl Environ Microbiol. 2020 Apr 17;86(9):e02981-19. doi: 10.1128/AEM.02981-19. Print 2020 Apr 17.

Authors

Hao Wu^#^{1

2}, Ershu Xue^#^{1

2}, Ning Zhi^{1

2}, Qianqian Song^{1

2}, Kairen Tian^{1

2}, Qinggele Caiyin^{1

2}, Lin Yuan¹, Jianjun Qiao^{3

2

4}

Affiliations

¹ Department of Pharmaceutical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.
² Key Laboratory of Systems Bioengineering, Ministry of Education, Tianjin, China.
³ Department of Pharmaceutical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin, China jianjunq@tju.edu.cn.
⁴ SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, China.

^# Contributed equally.

Abstract

Lactococcus lactis encounters various environmental challenges, especially acid stress, during its growth. The cell wall can maintain the integrity and shape of the cell under environmental stress, and d-amino acids play an important role in cell wall synthesis. Here, by analyzing the effects of 19 different d-amino acids on the physiology of L. lactis F44, we found that exogenously supplied d-methionine and d-phenylalanine increased the nisin yield by 93.22% and 101.29%, respectively, as well as significantly increasing the acid resistance of L. lactis F44. The composition of the cell wall in L. lactis F44 with exogenously supplied d-Met or d-Phe was further investigated via a vancomycin fluorescence experiment and a liquid chromatography-mass spectrometry assay, which demonstrated that d-Met could be incorporated into the fifth position of peptidoglycan (PG) muropeptides and d-Phe could be added to the fourth and fifth positions. Moreover, overexpression of the PG synthesis gene murF further enhanced the levels of d-Met and d-Phe involved in PG and increased the survival rate under acid stress and the nisin yield of the strain. This study reveals that the exogenous supply of d-Met or d-Phe can change the composition of the cell wall and influence acid tolerance as well as nisin yield in L. lactisIMPORTANCE As d-amino acids play an important role in cell wall synthesis, we analyzed the effects of 19 different d-amino acids on L. lactis F44, demonstrating that d-Met and d-Phe can participate in peptidoglycan (PG) synthesis and improve the acid resistance and nisin yield of this strain. murF overexpression further increased the levels of d-Met and d-Phe incorporated into PG and contributed to the acid resistance of the strain. These findings suggest that d-Met and d-Phe can be incorporated into PG to improve the acid resistance and nisin yield of L. lactis, and this study provides new ideas for the enhancement of nisin production.

Keywords: Lactococcus lactis; acid resistance; cell wall; d-amino acid; nisin.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Acids / metabolism*
Cell Wall / physiology*
Lactococcus lactis / metabolism*
Methionine / metabolism*
Nisin / biosynthesis*
Phenylalanine / metabolism*

Substances

Acids
Nisin
Phenylalanine
Methionine