Arsenic removal using Chlamydomonas reinhardtii modified with the gene acr3 and enhancement of its performance by decreasing phosphate in the growing media

Arsenic contamination of groundwater is a significant problem in countries like Mexico, where San Luis Potosi is among the regions registering severe levels of it. Bioremediation with microalgae capable to absorb and metabolize metals or metalloids like arsenic reduces their toxicity and is a cost-effective approach compared to physical-chemical processes. We evaluated the capability of Chlamydomonas reinhardtii to remove arsenate and compared it with an acr3-modified recombinant strain, which we produced by transforming the wild-type strain with Agrobacterium tumefaciens using the construct pARR1 including a synthetic, optimized acr3 gene from Pteris vittata, a hyper-accumulator of arsenic. We monitored the growth of both strains in media with arsenate, containing a standard or a 10-fold decreased amount of phosphate. Comparing both strains in media initially with 0.5, 1, and 1.5 mg/L of arsenate, the acr3-modified strain removed 1.5 to 3 times more arsenic than the wild-type strain. Moreover, the arsenic uptake rate increased 1.2 to 2.3 times when growing the acr3-modified strain in media with decreased phosphate, while the uptake rate for the wild-type strain scarcely changed under the same conditions. These results confirm the expression of the acr3 gene in C. reinhardtii and its potential application to remove arsenic.