Differential Expression of Proteins and Genes in the Lag Phase of Lactococcus lactis subsp. lactis Grown in Synthetic Medium and Reconstituted Skim Milk

Abstract

We investigated protein and gene expression in the lag phase of Lactococcus lactis subsp. lactis CNRZ 157 and compared it to the exponential and stationary phases. By means of two-dimensional polyacrylamide gel electrophoresis, 28 highly expressed lag-phase proteins, implicated in nucleotide metabolism, glycolysis, stress response, translation, transcription, cell division, amino acid metabolism, and coenzyme synthesis, were identified. Among the identified proteins, >2-fold induction and down-regulation in the lag phase were determined for 12 proteins in respect to the exponential phase and for 18 proteins in respect to the stationary phase. Transcriptional changes of the lag-phase proteins in L. lactis were studied by oligonucleotide microarrays. Good correlation between protein and gene expression studies was demonstrated for several differentially expressed proteins, including nucleotide biosynthetic enzymes, adenylosuccinate synthase (PurA), IMP dehydrogenase (GuaB), and aspartate carbamoyl transferase (PyrB); heat-shock protein DnaK; serine hydroxymethyl transferase (GlyA); carbon catabolite control protein (CcpA); elongation factor G (FusA); and cell division protein (FtsZ).Intracellular events occurring in bacteria just after introduction to a new environment provide the first evidence about physiological changes in the cells. When lactic acid bacteria are used as starter cultures, these intracellular changes may ensure a rapid prediction of the overall physiological status of the culture, which in turn defines the activity of the culture. Upon inoculation, the culture is exposed to massive environmental changes including nutrient availability, temperature, and pH. To adapt to new environments, bacteria have developed various metabolic responses. Recent research revealed a number of responses in Lactococcus lactis caused by exhaustion of essential nutrients such as purines (1), carbohydrates (7,18,36), and branched amino acids (10, 29), as well as responses to the temperature shift (6, 42), low pH (4,23,26,31), and a combination of these factors (13,25). However, only a few papers describe the intracellular changes occurring early in the cultivation upon transfer of the culture to a new rich medium. For example, proteomic research carried out with Lactobacillus delbrueckii subsp. bulgaricus showed that several proteins were strongly expressed in the lag phase, although only one protein (phosphoryl carrier protein HPr) was positively identified (30). Expression studies of Saccharomyces cerevisiae revealed about 20 proteins induced in the lag phase, which were primarily involved in protein synthesis, biosynthesis of amino acids, and carbohydrate metabolism (2, 3). A recent transcriptional study of Bacillus licheniformis based on 250 DNA probes exposed at least 15 differentially expressed genes of diverse functions in the lag phase (14).In this work, we investigated protein and gene expression in Lactococcus lactis subsp. lactis CNRZ 157 in the lag phase in comparison to the exponential and stationary growt...

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