Genome-wide transcriptional analysis of temperature shift in L. interrogans serovar lai strain 56601

Abstract

Background: Leptospira interrogans is an important mammalian pathogen. Transmission from an environmental source requires adaptation to a range of new environmental conditions in the organs and tissues of the infected host. Several studies have shown that a shift in culture temperature from 28 degrees C to 37 degrees C, similar to that encountered during infection of a host from an environmental source, is associated with differential synthesis of several proteins of the outer membrane, periplasm and cytoplasm. The whole genome of the Leptospira interrogans serogroup Icterohaemorrhagiae serovar lai type strain #56601 was sequenced in 2003 and microarrays were constructed to compare differential transcription of the whole genome at 37 degrees C and 28 degrees C.

Results: DNA microarray analyses were used to investigate the influence of temperature on global gene expression in L. interrogans grown to mid-exponential phase at 28 degrees C and 37 degrees C. Expression of 106 genes differed significantly at the two temperatures. The differentially expressed genes belonged to nine functional categories: Cell wall/membrane biogenesis genes, hemolysin genes, heat shock proteins genes, intracellular trafficking and secretion genes, two-component system and transcriptional regulator genes, information storage and processing genes, chemotaxis and flagellar genes, metabolism genes and genes with no known homologue. Real-time reverse transcription-PCR assays confirmed the microarray data.

Conclusion: Microarray analyses demonstrated that L. interrogans responds globally to temperature alteration. The data delineate the spectrum of temperature-regulated gene expression in an important human pathogen and provide many new insights into its pathogenesis.

Figure 1

correlation of microarray and Real-time PCR. Comparison of transcription measurements by microarray (red bar) and real-time PCR assays (blue bar). The fold change ratios are shown for nine genes at 37°C compared with 28°C.

Figure 2

Comparison of transcription measurements by microarray and real-time PCR assays. The relative transcriptional levels for the 9 genes listed in Figure 1 were determined by microarray and real-time RT-PCR. The real-time RT-PCR log₂ values were plotted against the microarray data log₂ values. The correlation coefficient (R²) between the two datasets is 0.8267.

Figure 3

functional categories. Genes differentially expressed at 37°C and 28°C, grouped by functional classification according to the NCBI L. interrogans 56601 COGs database . Genes were regarded as differentially expressed when the expression levels differed by at least twofold. The number of upregulated (red bars) and downregulated (blue bars) genes in each functional group is shown.