Temperature-dependent expression of Listeria monocytogenes internalin and internalin-like genes suggests functional diversity of these proteins among the listeriae

Abstract

The Listeria monocytogenes genome contains genes encoding several internalins and internalin-like proteins. As L. monocytogenes is present in many environments and can infect numerous, diverse host species, the environmental temperature was hypothesized to be a signal that might affect internalin gene transcription. A subgenomic microarray was used to investigate temperature-dependent transcription of 24 members of the internalin gene family in L. monocytogenes 10403S. The levels of internalin gene transcripts for cells grown at 37 degrees C were compared to the levels of transcripts for cells grown at 16, 30, and 42 degrees C using competitive microarray hybridization, and the results were confirmed by performing quantitative reverse transcriptase PCR for 14 internalin genes. Based on these studies, the internalin genes can be grouped into the following five temperature-dependent categories: (i) four sigma(B)-dependent internalin genes (inlC2, inlD, lmo0331, and lmo0610) with the highest levels of transcripts at 16 degrees C and generally the lowest levels of transcripts at 37 degrees C; (ii) three partially PrfA-dependent internalin genes (inlA, inlB, and inlC) with the lowest levels of transcripts at 16 degrees C and the highest levels of transcripts at 37 and 42 degrees C; (iii) four genes (inlG, inlJ, lmo0514, and lmo1290) with the lowest levels of transcripts at 16 degrees C and the highest levels of transcripts at 30 and/or 37 degrees C; (iv) one gene (lmo0327) with the highest levels of transcripts at 16 degrees C and low levels of transcripts at higher temperatures; and (v) 12 internalin genes with no differences in the levels of transcripts at the temperatures used in this study. The temperature-dependent transcription patterns suggest that the relative importance of different internalins varies by environment, which may provide insight into the specific functions of these proteins.

FIG. 1.

Line plots of pooled, log-transformed absolute levels of transcripts for gap (▪) and rpoB (○) and the geometric mean for rpoB and gap transcript levels (). The levels of transcripts were determined by qRT-PCR for L. monocytogenes 10403S grown to the early stationary phase at 16, 30, 37, or 42°C. The error bars indicate one standard deviation based on three independent replicates.

FIG. 2.

Normalized, log-transformed levels of transcripts for category I genes (A), category II genes (B), selected category III genes (C), and selected category IV genes (D). For details, see Table 2. Levels of transcripts were determined by qRT-PCR for L. monocytogenes 10403S grown to the early stationary phase at 16, 30, 37, or 42°C. The data are average log-transformed levels of transcripts (normalized to the geometric mean for rpoB and gap) for three independent replicates (i.e., three RNA isolations performed on different days); the error bars indicate one standard deviation. For each gene, Tukey's multiple-comparison procedure was used to determine whether the levels of transcripts of the gene differed at the four temperatures; different letters above bars indicate that the levels of transcripts were significantly different (P < 0.05), while identical letters above bars indicate that the levels of transcripts were not significantly different. NS, levels of transcripts at the different temperatures were not significantly different.