Short communication: Global transcriptome analysis of Lactococcus lactis ssp. lactis in response to gradient freezing

Abstract

Lactic acid bacteria are often preserved as starter cultures by freezing to extend shelf stability as well as maintain cell viability and acidification activity. Previous studies showed that the endocyte extracted from gradient-freezing pretreated cells could act as lyoprotectant in the lyophilization process of Lactococcus lactis ssp. lactis. In this study, the molecular mechanisms of L. lactis in response to gradient freezing exposure are described using high-throughput sequencing. Nineteen of 56 genes were upregulated after gradient freezing, whereas 37 genes were downregulated. Further validation results of quantitative real-time PCR experiments were consistent with the RNA sequencing. Gene Ontology (http: / / www .geneontology .org/ ) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG; https: / / www .genome .jp/ kegg/ ) pathway were used to analyze the differentially expressed genes. Several pathways, such as glutathione metabolism, ATP-binding cassette transport, metabolism of cell wall and cell membrane components, and stress response-related pathways, were affected by gradient freezing. Six genes relevant to freezing stress response were selected for quantitative real-time PCR, including 3 upregulated genes (hisK, eutD, dukA) and 3 downregulated genes (als, yedF, pepN). The Gene Ontology enrichment and KEGG pathway analyses showed these genes may influence stress response-related pathways, improving the survival of the L. lactis under freezing stress. The identification of these genes deepened an understanding about their response under freezing stress, helping us find potential genes or pathways related to gradient freezing for further research on lyoprotectants.

Omics Approaches to Assess Flavor Development in Cheese

“…Regarding cheese microbiota, the majority of the transcriptomic studies have been performed on L. lactis , due to its importance in cheese production [ 120 , 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 , 169 ]. In particular, the transcriptional responses of L. lactis have been investigated during different stresses, such as cold, heat, acid, osmotic, oxidative, and starvation [ 170 , 171 , 172 , 173 , 174 , 175 , 176 ], or during growth in media with different carbon sources [ 177 , 178 , 179 ]. Apart from L. lactis , transcriptomics studies have also been performed in other important cheese bacterial [ 163 , 180 , 181 , 182 , 183 , 184 , 185 , 186 ], yeasts [ 187 , 188 , 189 ], and fungal species [ 190 , 191 , 192 , 193 , 194 , 195 , 196 ].…”

Integrated metabonomic-proteomic analysis reveals the effect of glucose stress on metabolic adaptation of Lactococcus lactis ssp. lactis CICC23200

“…As previously shown, histidinol phosphatase (hisK) was up-regulated in L. lactis ssp. lactis in response to gradient freezing stress (Lu et al, 2019). Lysine biosynthesis might be responsible for the high-glucose stress tolerance of C. glycerinogenes (Yang et al, 2018).…”