Response Of Environmental Organisms To Nano-materials And Their Biosynthesis And Applications

Fabricated nanomaterials with unique physical,chemical properties and excellent performance are playing increasing roles in the fields of energy,material,machinery,biomedical imaging and drug delivery,etc.which are involved in the human's life.In the rapid development and applications of nanotechnology various nanomaterials have been introduced into the environment,causing great concerns over their environmental safety.In order to improve the environmental friendliness and biocompatibility of nanomaterials,understanding the interactions between nanomaterials and biological systems and their response mechanism is essential,as its can provide feedback to improve the synthesis method and further promote the application of nanotechnology.Focusing on the interaction between nanomaterials and organisms,this dissertation aims to investigate the response of environmental organisms to nano materials,and the synthesis and applications of bio-nanomaterials with three different types of biological systems.The main contents and results of this dissertation are listed below:1.Response of environmental mixed microbes to nanomaterials.When microbes encounter hazardous exogenous materials,a series of defensive manoeuvres could be induced to reduce the toxic effects and maintain their functions.Here,the response of methanogenic sludge exposed to single wall carbon nanotubes(SWCNTs)in an anaerobic reactor was investigated by a suite of analyses,including biochemical characterization,microbial community compositions,morphology and conductivity.The results show that SWCNTs at a concentration up to 1000 mg/L had no significant impact on the maximum methane yield.In contrast,they induced much faster substrate utilization and methane production rates,which might due to two main reasons.First,more extracellular polymeric substances(EPS)were excreted from the anaerobic sludge and closely interacted with SWCNTs.Such an interaction prevented nanoparticles from piercing into cells,and thus reduced their cytotoxicity.Secondly,in the compact anaerobic granule structure,such densely wrapped SWCNTs enhanced the electrical conductance of the sludge,which might promote direct interspecies electron transfer among anaerobic fermentative bacteria and methanogens in the anaerobic digestion process and resulted in more rapid methane generation.This work provides useful information to understand the response of microbes to CNTs in complex environmental matrix,which may show potential function-promoting behaviors.2.Biosynthesis of quantum dots(QDs)by Caenorhabditis elegans.When exposed to toxic heavy metals,a series of detoxification processes could be activated in microbes to capture free heavy metal ions,resulting in the formation of inorganic nanomaterials in vivo.Here,high-quality CdSe quantum dots(QDs)with yellow-green fluorescence were synthesized by the miniature model animal Caen.orhabditis elegans(C.elegans).With in-situ fluorescence imaging and elemental analysis in Shanghai Synchrotron Radiation Facility,the entire synthesis processes and the dynamic change of element Se were tracked.The morphology,crystal form,phase and fine structure of Se atom were characterized by Raman spectra,transmission electron microscope,inductively coupled plasma-Atomic emission spectrometer(ICP-AES)and extended X-ray absorption fine structure(EXAFS)spectra.The results show that CdSe QDs were formed in the pharyngeal tissues and intestine frontier of nematodes at the early stage,followed by expanding to the entire body later,and excreted outside the body at the latter synthesis stage.The synthesized QDs corresponded to hexagonal cadmoselite and their local Se structures of the sample consisted of approximately 4 Cd atoms at 2.62 A,with CdS formed simultaneously as a cape.These results demonstrate the great potential of QDs biosynthesis by nematode.Since C.elegans possess highly homologues genes and unique biological features relevant to human diseases,this work might be expanded to other high-level organisms for biochemical studies,and even provide important implications for human-body detoxification.3.Molecular-level mechanisms of CdSe QDs synthesis in C.elegans.To better understand the mechanism for CdSe QDs synthesis in nematode,we monitored the variations of thiol content and expression of relevant genes.Results show that the Se-only exposure increased the total thiols(TSH)content relative to the control,but a substantially lower reduced thiols(RSH)level due to the consumption of reduction equivalent for SeO32-reduction,which resulted in the organoselenium accumulation.A further Cd exposure increased the TSH content more remarkably,and most of thiol components remained at the reduced state,indicating that the reaction between organoselenium compounds and Cd facilitated the production of RSH and TSH in nematodes.The raised levels of RSH,TSH and organoselenium compounds in turn increased the Cd-Se interaction,leading to the accumulation of more Cd in the Se&Cd over the Cd-only group.The subsequent Cd exposure led to the substantially increased transcriptional response of mtl-7,mtl-2,gcs-1,while the Cd-only group increased even more;but the pcs-1 level increased drastically with QDs synthesis,suggesting a critical role of phytochelatins(PCs)at the later stage of CdSe biosynthesis.With transcriptome sequencing,the impacts of QDs synthesis on other gene expression were evaluated.The results indicate that the exposure to Na2SeO3 at 200 ?M had very little effect on the gene expression involved in the basal metabolism pathway,while 250 ?M Cd2+ showed significant inhibitory effect.In addition,Cd exposure exhibited intense stimulation on metabolic pathway of cytochrome P450 and GSH,which are involved in the detoxification of xenobiotics.4.The roles of several thiol-capping peptides in QDs biosynthesis.With biomimetic synthesis in vitro and density functional theory(DFT)calculations,the different roles of glutathione(GSH),phytochelatins(PCs)and metallothioneins(MTs)in the QDs synthesis process were explored.The successful CdSe synthesis in vitro further confirms that PCs are capable of reducing SeO32-to form CdSe under mild conditions.A analysis of energy changes of Cd2+-binding process and further combination with organoselenium compounds(e.g.,Selenocysteine,Sec)in aqueous solution show that PC2 is more thermodynamically favorable for binding Cd2+ than GSH,and PC2-Cd2 complex with two thiol groups of PC2 separately connected with two Cd2+ acted more easily to further connect on Sec than MT-Cdn.This result indicates that PC2 plays a dominant role in providing the temporary storage for Cd2+to drive the formation of CdSe bio-QD greatly,and gives a molecular-level explanation for the role of PCs secreted by C.elegans as a key participator involved in heavy metal detoxification and synthesizing CdSe bio-QD.5.Combination and application of polyvalent phages with magnetic nanoclusters.Microbes could take full advantages functional nanomaterials to deal with complicated environmental pollution problems.Here,a new method was developed for efficient removal of biofilm on carrier surface,by using the specific recognition of polyvalent phages combined with magnetic nanoclusters.Results show that polyvalent phage PEL1(Podoviridae family)was immobilized to magnetic nanoclusters via covalent bonding through amide linkages.The amino-modified and rough surface of the nanocluster facilitated the conjugation with phages,yielding about(5.2 ± 0.7)× 106 PFU of phage on 1 mg microsphere for CS-Fe3O4.In biofilm removing tests,PELT-CS-Fe3O4 achieved 88.7±2.8%removal of the pre-exiting mixed-species biofilm on glass surface after 6-h treatment.This mainly benefited from the ability of phages to lyse host cells,effective enrichment of phages and orientation control from magnetic nanoclusters,and mechanical disruption of biofilm matrix by the transportation of phage-magnetic nanocluster complex.Overall,magnetic orientation control could enhance the efficacy of phages and extend their application by enhancing their penetration into bio films and their delivery to relatively inaccessible locations.Also,this method can deal with multi-drug-resistant biofilms regardless of antibiotic resistance strains.