Table 2 Physical and chemical parameters of the three sHSPs from A. ferrooxidans. Gene Length Molecular weight (Da) Theoretical pI Identity/similarity to Afe_1009 Identity/similarity to Afe_1437 Identity/similarity NVP-BGJ398 to Afe_2172 Afe_1009 145 16934 6.20 – 29/58% 26/47% Afe_1437 148 16680 5.43 29/58% – 22/53% Afe_2172 134 16401 5.60 26/47% 22/53% – Afe_1009, Afe_1437, and Afe_2172 are not organized in an operon in the A. ferrooxidans genome. Indeed, most of the known sHSP genes are not arranged in operons
[33, 34], with some exceptions such as the Escherichia coli ibpAB operon, which contains two sHSP genes (ibpA and ibpB) [35, 36], and Bradyrhizobium japonicum, which has sHSP genes found as independent units and others grouped in the same operon . sHSP genes expression in A. ferrooxidans LR cells subjected to heat shock qRT-PCR was used to determine the transcript levels of the Afe_1009, Afe_1437, and Afe_2172 genes in A. ferrooxidans LR cells LY2874455 grown at 30°C (control) or subjected to a 40°C heat shock for 15, 30 and 60 minutes (Figure 1). The qRT-PCR results indicate that after 60 minutes all three sHSP genes were significantly up-regulated
(p < 0.05 and fold change ≥ 2.0), although the expression level of Afe_2172 was considerably lower than the expression levels of Afe_1437 and Afe_1009. The expression level for Afe_1437 was 20-fold higher than that observed for Afe_2172, and 11.5-fold higher than the expression level of Afe_1009. Xiao et al.  observed a similar pattern Aurora Kinase of expression for the Afe_1437 gene. Our results
for Afe_1009 and Afe_2172 were dissimilar to those obtained by Xiao et al. . However, this comparison may not be reliable due to differences in the A. ferrooxidans strains as well as the heat shock experiments used in the two studies. Figure 1 Expression of the shsp genes from A. ferrooxidans LR. Expression of the genes located at loci Afe_1009, Afe_1437, and Afe_2172 in A. ferrooxidans LR cells submitted to heat shock (40°C) at different times (15, 30, and 60 min). The expression values, obtained by Real time PCR, are relative to the ones obtained from cells maintained at 30°C. The observed differences in the expressions of the three A. ferrooxidans sHSP genes suggest possible regulatory differences. In many bacteria, the σ32 factor regulates the expression of the sHSP-encoding genes in a temperature-dependent manner . Under stress conditions, the transcription of heat shock genes is induced following a rapid and transient increase of this factor . A bioinformatics analysis was therefore performed in the deduced -10 and -35 regions of the three sHSP genes. The results indicated that the three genes had possible σ32-dependent promoters (Figure 2). In the work undertaken by Xiao et al. , σ32-dependent promoters were only found for the Afe_1437 and Afe_2172 genes. However, the disparities between the two studies can be explained by the different in silico strategies chosen.