Effects of a Symbiotic Bacterium on the Accumulation and Transformation of Arsenate by Chlorella salina

Abstract

Algae-bacteria consortia may be potentially applied in wastewater treatment and environment remediation. In this study, in order to investigate effects of a symbiotic bacterium on the accumulation and transformation of arsenate[As(Ⅴ)] by Chlorella salina, we used batch cultures to determine the uptake, adsorption and transformation of As by axenic and non-axenic C. salina exposed to 0-750 μg·L-1 As(Ⅴ) for 7 d. The symbiotic bacterium of C. salina was confirmed to be Halomonas sp. after isolation, cultivation and 16S rRNA identification. The bacterial presence markedly increased the adsorption of As in C. salina, but it markedly reduced the absorption and the toxic effect of As(Ⅴ). Arsenate was the major arsenic species in the cells of axenic and non-axenic C. salina. The proportion of arsenite[As(Ⅲ)] was 8.99%-11.52% in the axenic microalga whereas a small quantity of monomethylarsonous acid (MMA) and dimethylarsinous acid (DMA) (0.02%-0.04%) were detected in the non-axenic counterpart. As(Ⅲ) dominated the As speciation in the bacterial culture and the percentage of As(Ⅴ) was 7.59%-26.80%, indicating that this symbiotic bacterium had a strong As(Ⅴ) reducing ability. The As removal rate (19.81%-41.08%) by non-axenic C. salina was higher than the bacterium alone (5.14%-14.62%) and axenic C. salina (14.98%-21.08%) after 7 d As(Ⅴ) exposure. The symbiotic Halomonas sp. promoted the accumulation of As by C. salina, indicating that algae-bacteria consortia might enhance the bioremediation of As contaminated water.