Characterization Of Bacterial Generated Selenium-based Nanomaterials And Their Photocatalytic/Photothermal Conversion Activity

Selenium-reducing bacteria?SeRB?are microorganisms that can reduce selenite and selenate to elemental selenium or selenides.Nowdays,there are many researches about the synthesis of selenium by SeRB.However,there are few studies about the types,morphology control and reduction mechanism of selenium-based nanomaterials synthesized by microorganisms.In this paper,two SeRB were isolated from marine sediment sediments in Liaodong Bay.The two strains were identified by 16S rRNA gene sequence analysis and designated as Lysinibacillus sp.ZYM-1 and Bacillus cereus CC-1,respectively.To investigate the putative functional genes of selenate and selenite reduction,the genome sequencing of strain ZYM-1and CC-1 showed that the strain ZYM-1 contains genes coding glutathione reductase,thioredoxin reductase,flavin oxidoreductase,nitrite reductase;narG-narH-narJ-narI was found in the CC-1 genome,which encodes the complete respiratory nitrate reductase,indicating that these enzymes may play an important role in selenate and selenite reduction in the two strains.Meanwhile,both strains contain a large amount of heavy metal tolerance and translocation related genes,indicating that the strains have the potential to tolerate a variety of heavy metals.Subsequently,the performance of two strains to reduce selenite was investigated and found,finding that strain ZYM-1 and CC-1 can reduce selenite over a wide range of pH?5-9?,selenite concentration?1-25 mmol/L?within 48 h to selenium nanoparticles?Selenium nanomaterails,Se NMs?.Compared with strain CC-1,strain ZYM-1 has slightly higher reducing ability.Therefore,the Se NMs synthesized by strain ZYM-1 under different conditions were characterized.The results showed that the morphology and size of Se NMs were dependent on medium composition,pH,incubation time,and selenite concentration.Se nanospheres?Se NSs?exhibited significant visible light-driven photocatalytic activity on Rhodamine B?RhB?with H₂O₂.Three N-deethylation intermediates and phthalic acid were identified as degradation products of RhB by using liquid chromatography-high resolution mass spectrometry?LC-HRMS?,indicating the coexistence of chromophore cleavage and the N-deethylation pathway.Finally,the experiment explored the feasibility of synthesizing metal selenide by strain ZYM-1 and CC-1.Bismuth selenide namomaterials?Bi₂Se₃ NMs?were focused,finding that morphology,size and location of the biogenic Bi₂Se₃ are bacteria-dependent.It is difficult to separate Bi₂Se₃ generated by strain CC-1?Bi₂Se₃-C?from the biomass due to strong interaction with the cell membrane.However,Bi₂Se₃ produced by strain ZYM-1?Bi₂Se₃-Z?are highly dispersed in extracellular space with high stability.Further characterization of Bi₂Se₃-Z indicates that the product is rhombohedral phase,ultrathin nanosheet-like structure with an average size of 60 nm.Subsequently,the photothermal performance of Bi₂Se₃-Z with the irradiation of 808 nm near infrared laser was determined.When the Bi₂Se₃-Z concentration was26 mg/L,and irradiation power power was 2 W,100%of human breast cancer cells MCF-7 and lung carcinoma cells A549 were killed within 10 min irradiation in vitro.Moreover,using 1%?v/v?PVP as surfactant,a novel nanodumb-bells structure of Bi₂Se₃ was obtained.