Engineering heavy metal resistance in cyanobacteria Synechococcus elongatus PCC7942

Cyanobacteria;heavy metal;polyphosphate;ppk gene

Chen, Xiaolun ; Bhalerao ; Kaustubh

关键词: Cyanobacteria;    heavy metal;    polyphosphate;    ppk gene;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45367/Xiaolun_Chen.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Cyanobacteria are a large and diverse group of photosynthetic prokaryotes, which are adapted to various habitats and play an important role in any ecosystem. These organism encounter various environmental pressures, including heavy metal toxicity which can be significant. One of the possible mechanisms of heavy metal detoxification is chelation of the metal ions by endogenous polyphosphate. This study is an evaluation of nanoparticle toxicity that contains heavy metal cores from the perspective of polyphosphate-based chelation. Cadmium was chosen as the toxic heavy metal and the cyanobacterium Synechococcus elongatus PCC7942 was chosen as the model organism for its ability to be genetically engineered. This study tried different methods to generate heavy metal resistant cyanobacteria strains, including continuous exposure the culture to cadmium ions, and genetically overexpressing polyphosphate kinase gene to increase polyphosphate production in cyanobacteria. Cell growth was evaluated by optical density, and photosynthetic system activity was measured by using fluorescence spectral analysis. Morphological changes of the cells were observed by transmission electron microscopy. Cyanobacteria Se7942 developed cadmium resistance after being exposed to low concentration of Cd ions for 6 generations, which significantly reduced thedamage to photosynthetic system due to cadmium. Similar resistance was observed in genetically engineered Se7942 overexpressing polyphosphate kinase gene. The engineered strains produced a higher level of inorganic polyphosphate, which seemed to help the heavy metal detoxification. The PPK strain showed a higher tolerance to cadmium than wild-type and naturally evolved resistant strain. The primary argument in this thesis is that polyphosphate-based heavy metal chelation may be amenable to engineering and could lead to synthetic biology approaches to bioremediation.