Global transcriptome analysis of the heat shock response of Bifidobacterium longum

Abstract

Bifidobacteria are natural inhabitants of the human gastrointestinal tract and have been widely used as functional foods in different products. During industrial processing, bacterial cells undergo several stresses that can limit large-scale production and stability of the final product. To better understand the stress-response mechanisms of bifidobacteria, microarrays were used to obtain a global transcriptome profile of Bifidobacterium longum NCC2705 exposed to a heat shock treatment at 50 degrees C for 3, 7 and 12 min. Gene expression data highlighted a profound modification of gene expression, with 46% of the genes being altered. This analysis revealed a slow-down of Bi. longum general metabolic activity during stress with a simultaneous activation of the classical heat shock stimulon. Moreover, the expression of several genes with unknown function was highly induced under stress conditions. Three of these were conserved in other bacteria species where they were also previously shown to be induced by high temperature, suggesting their widespread role in the heat stress response. Finally, the implication of the trans-translation machinery in the response of Bi. longum cells to heat shock was suggested by the induction of the gene encoding the tmRNA-associated small protein B (SmpB) with concomitant high constitutive expression of the tmRNA gene.

HspR Mutations Are Naturally Selected in Bifidobacterium longum When Successive Heat Shock Treatments Are Applied

“…We hypothesized that the increased heat resistance of the new strains resulted from a difference in the expression of genes involved in the stress response, compared to the parental strain previously investigated (27). Whole-genome expression analysis of the mutants versus that of the wt NCC2705 would then focus on what make these strains more resistant to HS.…”

“…In order to guarantee that the transcriptomic differences observed in the HS-tolerant mutants were relevant to their improved heat resistance, their phenotypes were validated in the same conditions: after 10 min of HS at 50°C, the viability of strain NCC2705 started an exponential decline and lost 2 log units after 50 min, whereas the viability of strains NCC2912 and NCC2913 remained unaffected (data not shown). For their transcriptomic analysis, the three strains were grown separately at 37°C in fermentors and harvested in mid-exponential phase with or without being subjected to HS, as previously described (27). Then, by microarray hybridizations, we compared the whole transcriptomes of these strains under two conditions, no HS and 7-min HS (Fig.…”

“…Whole-genome expression analysis of the mutants versus that of the wt NCC2705 would then focus on what make these strains more resistant to HS. In the documented HS study (27), a NCC2705 liquid culture was challenged in exponential phase at 50°C. In order to guarantee that the transcriptomic differences observed in the HS-tolerant mutants were relevant to their improved heat resistance, their phenotypes were validated in the same conditions: after 10 min of HS at 50°C, the viability of strain NCC2705 started an exponential decline and lost 2 log units after 50 min, whereas the viability of strains NCC2912 and NCC2913 remained unaffected (data not shown).…”

“…Gene expression measurement by qPCR. Three biological replicates of cultures in stationary phase were analyzed by quantitative PCR (qPCR) as previously described (27). Results were normalized with the housekeeping genes BL0301 and BL0118.…”

“…The genetic response of Bifidobacterium longum to heat shock (HS) was recently documented in its complexity (27,31). When doing a global transcriptomic analysis by microarrays, HS altered the transcription of 46% of the genes analyzed.…”