Effect Of NC₆₀ On The Growth And Metabolism Of Denitrifying Bacteria

Nanotechnology, considered as a technology which may change world, hasrapidly and dramatically developed in the past10years. And concerns on the potentialbiological effects of nanomaterials on the health of huaman and environment havebeen raised at the same time. Fullerene(C60) is a typical kind of nanomaterials that hasbeen widely used in practice. According to the estimation from Frontier CarbonCorporation, there are about10t of C60emitted to the environment each year,including soil, air and water. nC60is one of the most likely form of C60in theenvironment. Once entering aqueous environment, C60will form into stable colloidalsolution and exist in the aggregates form of5~500nm in size. nC60can cause toxiceffects on both eukaryotic and prokaryotic cells. As for prokaryotes, a basicagreement has been reached that nC60could inhibit the growth of certainmicroorganisms, such as E.coli K12, Bacillus subtilis. However, there is a dispute onthe biological effects of nC60. Some studies suggest that the survival rate of E.coliAMC198can be increased by nC60. Likewise, nC60does not affect the growth ofsome microorganisms such as Aeromonas sp.. Thus, the biological effects of nC60may depend on many aspects such as the subject organsims selected for study. In thepresent study, in order to assess the impact of nC60on ecosystem, denitrifyingmicroorganism community and pure cultures of bacteria isolated from the samecommunity were selected to explore the effect of nC60on both growth andmetabolism. Results showed that the biological effects of nC60are largely affected byenvironmental factors. In aerobic and acidic condition, nC60could significantly alterthe structure of denitrifying community. In the microbial community, Geobacillus sp.decreased in abundance due to nC60. Acidovorax sp., Cloacibacteria sp. and Bacillussp., however, increased in their abundance after the addition of nC60. Thisphenomenon indicates a possibility that nC60may inhibit the growth of certain bacteria and meanwhile promote the growth of some other bacteria. Using purecultures to examine the nC60biological effects, we found that nC60did not affect thegrowth Brucella sp.. However, the growth rate of E.coli could be changed by nC60.Most interestingly, Bacillus cereus increased in its biomass during plateau phase,showing a growth promoting effect of nC60. This novel effect can be influenced byconcentration of nC60. When concentration is less than3mg L-1, thisgrowth-promoting effect increased with a concentration-dependent manner. Whenconcentration is higher than7mg L-1, the growth-promoting effect, however,diminished with continuously increasing concentration. In terms of protein expression,the addition of high concentrations of nC60induced significantly increasedintracellular SOD activity of Bacillus cereus, from115U mL-1to130U mL-1. nC60can also cause a significant impact on denitrification capacity of Bacillus cereus.After adding5mg nC60L-1, the degradation rate of nitrate increased from55%to35%,while the cumulative nitrite reduced from33μg mL-1to25μg mL-1. These resultsindicate the possible presence of diverse biological functions of nC60. The presentstudy focuses on the promoting-effect of fullerene, and reveals the complexity of theecological effects that may caused by fullerene. The improvement in denitrificationability also suggests potential applications of fullerenes in the field of wastewatertreatment.