Study On The Responses Of Marine Microorganisms To Nano Titanium Dioxide

Recent years,nano titanium dioxide(nano-TiO2)is widely used in our daily life due to its special physical and chemical properties.However,regardless of its application,nano-TiO2 eventually flows into the marine environment,while its toxic effects on the marine environment is rarely reported.This paper investigated the effect of nano-TiO2 on marine microbes,including non-photosynthetic bacteria,photosynthetic bacteria,fungi and its toxic mechanism.In addition,it also studied about the influence of the nano-TiO2 on microbial community structure and biomass.The main results achieved in this work are listed as following:1.This paper evaluates the effect of nano-TiO2 on the growth and metabolism of six kinds of marine microorganisms,including Marinobacter sp.,Halomonas sp.,Alteromonas sp.,Vibrio parahaemolyticus,Rhodotorula sp.and marine cyanobacterial strain Synechococcus sp.,with Escherichia coli and Bacillus subtilis as reference strains.Concentrations of nano-TiO2 were tested from 0.1 to 100 mg/L.Growth curve,biomass and respiration intensity were measured to assess the effect of nano-TiO2 on the growth and metabolism of tested microorganisms.Photosynthetic activity was tested by the content of chlorophyll a in Synechococcus sp.The results showed that low concentrations(0.1?1 mg/L)of nano-TiO2 had little effects(p>0.05)on marine microorganisms,both in the light and dark conditions,while high concentrations(10?100 mg/L)of nano-TiO2 can decline the biomass and metabolism of marine microorganisms.The effects become more remarkable as the concentration of nano-TiO2 increased.And nano-TiO2 with high concentrations(100 mg/L)can decline the content of chlorophyll a in Synechococcus sp.XM-299.Short-term toxic effect of nano-TiO2 on most bacteria and Rhodotorula sp.showed significant difference(p<0.05)after 18 h,while the same effect is reflected after 6 d later for Synechococcus sp.(p<0.05).2.The effects of different concentration of nano-Ti02 on the mechanism of killing bacteria was evaluated by means of measuring the integrity of the cell wall and cell membrane.The experiments measuring the amounts of LDH and ROS showed that nano-TiO2 could damage cell wall and cell membrane by means of generating ROS,which had the effect of killing bacteria.High concentration of nano-TiO2(10?100 mg/L)have strong ability to destroy cell wall and cell membrane by producing ROS.3.This paper also investigated the effect of nano-Ti02 on marine microbial community composition in seawater under the simulated natural conditions by the technologies of high-throughput sequencing and qPCR after 7 and 14 days' incubation in the presence of nano-TiO2.The experiment indicated that the nano-TiO2 could cause the change of the microbial community structure in seawater,after incubation for 7 and 14 days,respectively.Nano-TiO2 with high concentration(10?100 mg/L)reduced the microbial community diversities,and 100 mg/L of nano-TiO2 significantly reduced microbial biomass(p<0.01).Nano-TiO2 with low concentration(<1 mg/L)could reduce microbial diversities at initial stages,but then decreased the microbial biomass significantly(p<0.05).In summary,this study can provide basic knowledge for assessing the effect of nano-Ti02 on marine ecological safety.