Global transcriptome analysis of Lactococcus garvieae strains in response to temperature

Abstract

Lactococcus garvieae is an important fish and an opportunistic human pathogen. The genomic sequences of several L. garvieae strains have been recently published, opening the possibility of global studies on the biology of this pathogen. In this study, a whole genome DNA microarray of two strains of L. garvieae was designed and validated. This DNA microarray was used to investigate the effects of growth temperature (18°C and 37°C) on the transcriptome of two clinical strains of L. garvieae that were isolated from fish (Lg8831) and from a human case of septicemia (Lg21881). The transcriptome profiles evidenced a strain-specific response to temperature, which was more evident at 18°C. Among the most significant findings, Lg8831 was found to up-regulate at 18°C several genes encoding different cold-shock and cold-induced proteins involved in an efficient adaptive response of this strain to low-temperature conditions. Another relevant result was the description, for the first time, of respiratory metabolism in L. garvieae, whose gene expression regulation was temperature-dependent in Lg21881. This study provides new insights about how environmental factors such as temperature can affect L. garvieae gene expression. These data could improve our understanding of the regulatory networks and adaptive biology of this important pathogen.

Figure 1. Comparison of the transcriptomic response of Lg8831 and Lg21881 grown at 18°C and 37°C.

Up 37°C and Up 18°C represent up-regulated genes at each temperature.

Figure 2. COG categories distribution of differentially expressed genes in Lg8831 and Lg21881 at 18°C and 37°C.

Bars indicate the number of genes up-regulated in each functional group at each temperature in Lg8831 (blue) and Lg21881 (orange).

Figure 3. Correlation between RT-qPCR and microarray analysis data.

The log₁₀ values of the real-time RT-qPCR were plotted against the microarray analysis log₁₀ values. The expression levels for 10 selected genes are shown.

Figure 4. Comparison of the expression levels of cold stress-related genes in Lg8831 and Lg21881 at 18°C and 37°C by microarray analysis.