Name: Ali Md Muntasir
Date: November 18, 2019
Campus Humanities, Sciences and Engineering
Vrije Universiteit Brussel
Novel metal resistance mechanisms of Cupriavidus metallidurans
bacteria, belonging to the Burkholderiaceae
family, are characterized by their resistance to multiple metals. In this work, the rapid evolution of C. metallidurans
towards significantly increased metal ion resistance was investigated by performing adaptive laboratory evolution experiments with silver and platinum.
For silver, the canonical resistance mechanisms did surprisingly not participate in this adaptive evolution. In contrast, a novel and unique resistance mechanism, with a pivotal role for small periplasmic proteins partially controlled by a two-component regulatory system, was discovered. As the formation of silver nanoparticles was observed, we hypothesize that this formation prevents ionic silver to exert its action in the cytoplasm and provides the ability to withstand much higher silver concentrations than efflux-mediated resistance. Binding and interaction of the involved two-component regulatory system AgrRS (and CzcR2S2) with DNA target sites was further scrutinized. Interestingly, the unphosphorylated response regulators were found to be the active form and high-resolution contact maps were obtained by various enzymatic and chemical footprinting and premodification binding interference techniques. These analyses led to a general regulation scheme in which AgrS inactivation mainly results in unphosphorylated AgrR that subsequently activates target genes, including that coding for a pivotal small periplasmic protein. Furthermore, our results show that there is crosstalk between the different two-component regulatory systems and redundancy in the adaptation to silver.
An evolved strain with increased resistance to platinum was also obtained. Since no canonical resistance mechanisms to platinum are known, it was studied using high-throughput genomic and transcriptomic sequencing. The latter showed pleiotropic alterations in membrane-related processes, such as pili, peptidoglycan turnover and electron transfer.
To conclude, this work unravelled the potential of C. metallidurans
to adapt to toxic metal ions and an unanticipated mechanism of resistance, showed the functionality of a novel protein family, and scrutinized the role of signal transduction.
- (VUB) Eveline Peeters
- (VUB) Daniël Charlier
Click here for a list of obtained PhD degrees.