Abstract
Epigallocatechin gallate (EGCG) is a main constituent of green tea polyphenols that are widely used as food preservatives and are considered to be safe for consumption. However, the underlying antimicrobial mechanism of EGCG and the bacterial response to EGCG are not clearly understood. In the present study, a genome-wide transcriptional analysis of a typical spoilage bacterium, Pseudomonas fluorescens that responded to EGCG was performed using RNA-seq technology. A total of 26,365,414 and 23,287,092 clean reads were generated from P. fluorescens treated with or without 1 mM EGCG and the clean reads were aligned to the reference genome. Differential expression analysis revealed 291 upregulated genes and 134 downregulated genes and the differentially expressed genes (DEGs) were verified using RT-qPCR. Most of the DGEs involved in iron uptake, antioxidation, DNA repair, efflux system, cell envelope and cell-surface component synthesis were significantly upregulated by EGCG treatment, while most genes associated with energy production were downregulated. These transcriptomic changes are likely to be adaptive responses of P. fluorescens to iron limitation and oxidative stress, as well as DNA and envelope damage caused by EGCG. The expression of specific genes encoding the extra-cytoplasmic function sigma factor (PvdS, RpoE and AlgU) and the two-component sensor histidine kinase (BaeS and RpfG) were markedly changed by EGCG treatment, which may play important roles in regulating the stress responses of P. fluorescens to EGCG. The present data provides important insights into the molecular action of EGCG and the possible cross-resistance mediated by EGCG on P. fluorescens, which may ultimately contribute to the optimal application of green tea polyphenols in food preservation.
Highlights
Contamination by pathogenic and spoilage bacteria is a major issue during food processing
RNA-seq using the Illumina paired-end sequencing technology was used to examine the effect of Epigallocatechin gallate (EGCG) on the P. fluorescens transcriptome
Among the P. fluorescens strains with complete genome sequence in GenBank, UK4 strain had the highest 16S gene homology with the test strain ZJL511, and the P. fluorescens UK4 strain sequence was used as the reference genome [35]
Summary
Contamination by pathogenic and spoilage bacteria is a major issue during food processing. The application of GTPs in the food industry has attracted more interest, especially in fish or meat products. Dip treatment with 0.2% GTP was effective in inhibiting spoilage bacteria growth and extending the ice storage life of fish samples to 35 days compared to 28 days for the control group [3]. GTPs were used combined with other natural preservatives. Application of GTPs (0.3% or 0.15%) in combination with 6-gingerol (0.3% or 0.15%) inhibited oxidation of protein and lipids, and reduced microorganism counts compared to control treatments during storage of shrimp paste [5]. The combination of nisin (0.625 g/L), GTPs (0.313 g/L) and chitosan (3.752 g/L) could be used as preservatives to efficiently inhibit the growth of spoilage microorganisms and pathogens in chilled mutton [6]. GTPs were considered to be a good choice of natural food preservatives, there were some challenges of the utilisation of GTPs in foods, such as the astringent and bitter taste [7], unstability during thermal processing and alkaline solutions [8,9], which may limit the application of GTPs in foods
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