Construction and characterization of an engineered recombinant Rhodopseudomonas palustris to remove Cd2+, Zn2+ and Cu2+

In this study, we used a photosynthetic bacteria as a host to construct a novel engineered bacterium Rhodopseudomonas palustris expressed with the metallothionein (MT) from the freshwater crab (Sinopotamon honanense), and to investigate its removal and biosorption capacity for Cd, Zn and Cu in medium and the possible mechanism(s). The results showed that: (i) the MT expressed recombinant was constructed successfully; (ii) the order of heavy metal sensitivity of the recombinant was Cd > Cu > Zn, and the maximum biosorption capacities calculated by Langmuir model were 224.22, 233.64 and 99.8 mg/g, respectively. Compared to the wild-type, the recombinant has doubled biosorption capacity to Cd and Cu with higher sorption rates and was less influenced by different culturing factors (time, metal concentration and pH), which allowed it rapid removal of 92.1% of 25 mg/L Cd within 30 mins; (iii) the recombinant exhibited more diverse biosorption patterns, and the proportion of its intracellular uptake was significantly (P < 0.05) increased 10% under different conditions; (iv) the functional groups on the cell membrane of the recombinant involved in the metal biosorption were more selective, and the synthesis of metal nanoparticles might be reused as optoelectronic materials for recycling. Based on the findings, we concluded that under various culturing conditions, the recombinant can remove the metals examined more successfully and efficiently. Therefore, as a novel strain, the recombinant has great potential for application in the removal and recovery of metals from wastewater or other polluted water sources.