Identification of Three Superoxide dismutase Genes from a Geobacillus sp

The phosphotransferase system gene ptsH plays an important role in MnSOD production, biofilm formation, swarming motility, and root colonization in Bacillus cereus 905

The rhizosphere bacterium Bacillus cereus 905 is capable of promoting plant growth through effective colonization on plant roots. The sodA2-encoding manganese-containing superoxide dismutase (MnSOD2) is important for survival of B. cereus 905 in the wheat rhizosphere. However, the genes involved in regulating sodA2 expression and the mechanisms of rhizosphere colonization of B. cereus 905 are not well elucidated. In this study, we found that the deletion of the ptsH gene, which encodes the histidine-phosphorylatable protein (HPr), a component of the phosphotransferase system (PTS), causes a decrease of about 60% in the MnSOD2 expression. Evidences indicate that the ptsH dramatically influences resistance to oxidative stress, glucose uptake, as well as biofilm formation and swarming motility of B. cereus 905. Root colonization assay demonstrated that ΔptsH is defective in colonizing wheat roots, while complementation of the sodA2 gene could partially restore the ability in utilization of arabinose, a non-PTS sugar, and root colonization caused by the loss of the ptsH gene. In toto, based on the current findings, we propose that PtsH contributes to root colonization of B. cereus 905 through multiple indistinct mechanisms, involving PTS and uptake of PTS-sugars, up-regulation of MnSOD2 production, and promotion of biofilm formation and swarming motility.

A novel mechanism of protein thermostability: a unique N-terminal domain confers heat resistance to Fe/Mn-SODs

Superoxide dismutases (SODs), especially thermostable SODs, are widely applied in medical treatments, cosmetics, food, agriculture, and other industries given their excellent antioxidant properties. A novel thermostable cambialistic SOD from Geobacillus thermodenitrificans NG80-2 exhibits maximum activity at 70°C and high thermostability over a broad range of temperatures (20–80°C). Unlike other reported SODs, this enzyme contains an extra repeat-containing N-terminal domain (NTD) of 244 residues adjacent to the conserved functional SODA domain. Deletion of the NTD dramatically decreased its optimum active temperature (OAT) to 30°C and also impaired its thermostability. Conversely, appending the NTD to a mesophilic counterpart from Bacillus subtilis led to a moderately thermophilic enzyme (OAT changed from 30 to 55°C) with improved heat resistance. Temperature-dependant circular dichroism analysis revealed the enhanced conformational stability of SODs fused with this NTD. Furthermore, the NTD also contributes to the stress resistance of host proteins without altering their metal ion specificity or oligomerisation form except for a slight effect on their pH profile. We therefore demonstrate that the NTD confers outstanding thermostability to the host protein. To our knowledge, this is the first discovery of a peptide capable of remarkably improving protein thermostability and provides a novel strategy for bioengineering thermostable SODs.