Geobacillin II

Catalases catalyze the decomposition of hydrogen peroxide into water and oxygen. We have characterized two manganese-catalases from Geobacillus thermopakistaniensis, CatGt and Cat-IIGt, which exhibited significant variation in their sequence, structure and properties. There was only 23% sequence identity between the two. The striking structural difference was the presence of an extended C-terminal domain in CatGt. Molecular modelling and docking studies revealed that deletion of the C-terminal domain removes non-specific binding, which results in increased substrate affinity. To verify experimentally, a C-terminal truncated version of CatGt, named as CatGt-ΔC, was produced in Escherichia coli and effects of deletion were analyzed. There was no significant difference in optimal pH, optimal temperature and substrate specificity of CatGt and CatGt-ΔC. However, Km value was reduced from 259 to 157 mM and CatGt-ΔC exhibited ~1.5-fold higher catalytic efficiency as compared to CatGt. Furthermore, removal of the C-terminal domain converted the tetrameric nature to monomeric, and reduced the thermostability of the truncated protein. These results demonstrate that C-terminal domain of CatGt might have little role in maintaining enzyme function but provides additional structural stability to the protein, which is a desired property for industrial applications.

This study deals with the preconcentrations of Ni(II) and Co(II) ions in real samples using the solid phase extraction method (SPE) before their determinations by inductively coupled plasma optical emission spectrometry (ICP-OES). Thermophilic bacterium Geobacillus stearothermophilus SO-20 (Accession number: KJ095002), loaded with Amberlite XAD-4, was utilized as a novel biosorbent. Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscope (SEM) were employed for the investigation of the bacterial surface before and after Ni(II) and Co(II) biosorption. The experimental parameters were examined to find the best conditions. The retained Ni(II) and Co(II) ions on the biosorbent were eluted by using 5.0 ml of 1.0 mol l-1 HCI as the best eluent. The sorption capacities were found to be 16.8 mg g-1 for Ni(II) and 21.6 mg g-1 for Co(II). It was also successfully used for the quantification of Ni(II) and Co(II) in a river water sample, some vegetables and soil.

The toxin-antitoxin (TA) systems have been attracting attention due to their role in regulating stress responses in prokaryotes and their biotechnological potential. Much recognition has been given to type II TA system of mesophiles, while thermophiles have received merely limited attention. Here, we are presenting the putative type II TA families encoded on the genomes of four Geobacillus strains. We employed the TA finder tool to mine for TA-coding genes and manually curated the results using protein domain analysis tools. We also used the NCBI BLAST, Operon Mapper, ProOpDB, and sequence alignment tools to reveal the geobacilli TA features. We identified 28 putative TA pairs, distributed over eight TA families. Among the identified TAs, 15 represent putative novel toxins and antitoxins, belonging to the MazEF, MNT-HEPN, ParDE, RelBE, and XRE-COG2856 TA families. We also identified a potentially new TA composite, AbrB-ParE. Furthermore, we are suggesting the Geobacillus acetyltransferase TA (GacTA) family, which potentially represents one of the unique TA families with a reverse gene order. Moreover, we are proposing a hypothesis on the xre-cog2856 gene expression regulation, which seems to involve the c-di-AMP. This study aims for highlighting the significance of studying TAs in Geobacillus and facilitating future experimental research.