Abstract
BackgroundPsychrotrophic lactic acid bacteria (LAB) species are the dominant species in the microbiota of cold-stored modified-atmosphere-packaged food products and are the main cause of food spoilage. Despite the importance of psychrotrophic LAB, their response to cold or heat has not been studied. Here, we studied the transcriptome-level cold- and heat-shock response of spoilage lactic acid bacteria with time-series RNA-seq for Le. gelidum, Lc. piscium, and P. oligofermentans at 0 °C, 4 °C, 14 °C, 25 °C, and 28 °C.ResultsWe observed that the cold-shock protein A (cspA) gene was the main cold-shock protein gene in all three species. Our results indicated that DEAD-box RNA helicase genes (cshA, cshB) also play a critical role in cold-shock response in psychrotrophic LAB. In addition, several RNase genes were involved in cold-shock response in Lc. piscium and P. oligofermentans. Moreover, gene network inference analysis provided candidate genes involved in cold-shock response. Ribosomal proteins, tRNA modification, rRNA modification, and ABC and efflux MFS transporter genes clustered with cold-shock response genes in all three species, indicating that these genes could be part of the cold-shock response machinery. Heat-shock treatment caused upregulation of Clp protease and chaperone genes in all three species. We identified transcription binding site motifs for heat-shock response genes in Le. gelidum and Lc. piscium. Finally, we showed that food spoilage-related genes were upregulated at cold temperatures.ConclusionsThe results of this study provide new insights on the cold- and heat-shock response of psychrotrophic LAB. In addition, candidate genes involved in cold- and heat-shock response predicted using gene network inference analysis could be used as targets for future studies.
Highlights
Psychrotrophic lactic acid bacteria (LAB) species are the dominant species in the microbiota of coldstored modified-atmosphere-packaged food products and are the main cause of food spoilage
P. oligofermentans grew slightly slower at cold-shock temperatures (0 °C, 4 °C, and 14 °C) compared to growth in control temperature (25 °C), but the difference was not statistically significant
The number of differentially expressed genes increased over time at 0 °C and 4 °C in all three species, while the number of differentially expressed genes decreased after the 35-min timepoint at 14 °C in Le. gelidum and P. oligofermentans, indicating that adaptation started after 35 min in these two species (Fig. 2)
Summary
Psychrotrophic lactic acid bacteria (LAB) species are the dominant species in the microbiota of coldstored modified-atmosphere-packaged food products and are the main cause of food spoilage. Despite the importance of psychrotrophic LAB, their response to cold or heat has not been studied. We studied the transcriptome-level cold- and heat-shock response of spoilage lactic acid bacteria with time-series RNA-seq for Le. gelidum, Lc. piscium, and P. oligofermentans at 0 °C, 4 °C, 14 °C, 25 °C, and 28 °C. Understanding gene expression mechanisms of these spoilage LAB is important, since MAP technology with combined cold storage has increased its popularity for preservation of minimally processed fresh foods. A better understanding of LAB genomics and especially mechanisms of cold-shock and stress adaptation is crucial for discovery of new methods of spoilage control
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