| Arsenic pollution in water has been increasingly and widely concerned by the society.The removal of arsenic by microalgae has become one of the purification methods for arsenic-contaminated water.However,the ability of microalgae to absorb and transform heavy metals is not conducive to the large-scale cultivation of economic microalgae,which will lead to the excessive arsenic concentration of microalgae products.How to reduce or remove arsenic content in microalgae products is a difficult problem in economic microalgae industry.In recent years,the removal of arsenic by sulfate-reducing bacteria has become a research hotspot.The high-salt growth environment of Dunaliella salina makes it difficult to remove arsenic with common sulfate-reducing bacteria.Therefore,in this study,the salt-tolerant sulfate-reducing bacterial flora/strains were isolated from the crystallization pool of solar saltern,and the changes of arsenic content in algal mud treated by immobilized sulfate-reducing bacterial flora/strains were analyzed,in order to provide a theoretical basis for solving the arsenic pollution problem in large scale cultivation.The stable salt-tolerant bacterial flora with the characteristics of sulfate-reducing bacteria(SRB)was obtained through habituated and enrichment culture from the crystallizing pool of coastal solar saltern.The 16 S r DNA sequences of salt-tolerant SRB flora were analyzed by high-throughput sequencing technology.The results showed that the species were classified into 1 Kingdom,17 Phyla,37 Classes,74 Orders,112 Families,157 Genera and 161 Species.The most abundant species in the bacterial community is the strain of Thalassobacillus.The species richness was high,but the species diversity was low.Based on fast growth rate and SRB characteristics,10 strains of salt-tolerant SRB were isolated and purified by the method of plate streaking.The strain No.6 with fastest growth was selected for the further study of molecular identification and physiological characteristics analysis.The results showed that the 16 S r DNA sequence of strain No.6 had the highest similarity with that of Staphylococcus epidermidis in NCBI database,the similarity was more than 99%,and the NJ Phylogenetic tree was classified as S.epidermidis.Therefore,the strain No.6 was identified as S.epidermidis SRB-6.The effect of different culture conditions on the growth of strain SRB-6 was analyzed by single factor method.The results showed that the strain SRB-6 was a medium temperature halophilic strain sensitive to p H value.The optimum culture temperature,initial p H value,culture salinity and inoculation amount were 37℃,8,12% and 4%,respectively.The immobilized SRB pellets of SRB flora,S.epidermidis SRB-6 and Morganella morganii Y-10 were prepared by polyvinyl alcohol and sodium alginate method,respectively.The results of the anaerobic treatment of algae mud with the immobilized SRB pellets showed that only the immobilized SRB pellets prepared by the flora and S.epidermidis SRB-6 isolated from the crystallization pool had the ability to remove arsenic and increase the content of β-carotene.Among them,S.epidermidis SRB-6 had better ability of arsenic removal,the arsenic removal rate was 16.55%,and β-carotene content increased 35.92%.Therefore,using salt-tolerant SRB to prepare immobilized pellets to treat the algal mud of Dunaliella salina can not only decrease arsenic content,but also improve the content of β-arotene. |
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