Interaction Of Deep-sea Cadmium Removal Bacteria Strain On Phosphorus And Cadmium Removal And Its Biological Mechanisms

In recent years,cadmium pollution caused by large-scale mining,industrial wastewater discharge and phosphorus fertilizer application has become increasingly serious.Cadmium,as a highly toxic heavy metal element,can accumulate in organisms after entering the food chain due to its non-degradability,causing serious health and ecological hazards.In nature,the distribution of phosphorus and cadmium has a certain correlation.The relationship between cadmium and phosphorus in seawater is bilinear.Cadmium in phosphate rock usually exists at the concentration of 0.1-60 mg/kg.In production,due to the exploitation of non-ferrous metal deposits and phosphate rock and the application of cadmium-containing phosphorus fertilizer,the wastewater containing cadmium contains phosphorus of different concentrations.In addition,phosphorus is also a non-renewable resource,and it is estimated that the currently exploitable phosphate rock resources worldwide will be exhausted in 60-130 years.Therefore,phosphorus recovery and simultaneous removal of phosphorus and cadmium in wastewater are of great significance in the protection of phosphorus resources and prevention of cadmium pollution.Microorganisms play an important role in the cycling of phosphorus and cadmium and the mineralization of phosphorus.The reported microorganisms that can remove phosphorus and cadmium at the same time are few and the species are not clear.Pseudoalteromonas sp.SCSE709-6(P.sp.SCSE709-6)is a highly efficient marine bacterium isolated from the South China Sea.Previous studies have found that P.sp.SCSE709-6 can achieve simultaneous removal of phosphorus and cadmium,but its mechanism and biological mechanism are still unclear in the process of simultaneous removal of phosphorus and cadmium.Based on the above research background,the phosphorus removal efficiency and its application of strain P.sp.SCSE709-6 were studied firstly;the effects of different phosphorus and cadmium concentrations on the physiological and biochemical characteristics of P.sp,SCSE709-6 and the removal efficiency of phosphorus and cadmium were further analyzed;and the biological mechanism of phosphorus and cadmium migration and transformation and P.sp.SCSE709-6 in the process of simultaneous removal was analyzed.The main research work and important conclusions of this paper include the following parts:(1)P.sp.SCSE709-6 has strong environmental adaptability and phosphorus removal ability.The phosphorus removal is mainly in the form of organic phosphorus(phosphoric monoester and phosphoric diphosphate)distributed on intracellular and extracellular polymers.The inoculation of P.sp.SCSE709-6 strengthens the system's ability to remove carbon and phosphorus and increases the similarity of microbial communities.P.sp.SCSE 709-6 can grow well at initial phosphorus concentration of 1-40 mg/L,salinity of 1%-10%,pH of 5-8.5,C/N ratio of 15-20 and temperature of 15-30 C,and achieve efficient phosphorus removal.The maximum phosphorus removal rate is about 30 mg/L.The strain has strong environmental adaptability and good phosphorus removal effect.In the process of phosphorus removal,orthophosphate gradually assimilates and absorbs into organic phosphorus.Organic phosphorus exists in the form of phosphoric monoester and phosphoric diphosphate,accounting for 92.82%-95.54%of total phosphorus.Phosphorus removal was mainly distributed in the cells and EPS,with the percentage of 41.3%and 50.6%respectively.The results of SMT extraction showed that phosphorus in bacteria mainly existed in the form of easily migrated and bio-available phosphorus(organic phosphorus OP and non-apatite phosphorus NAIP).accounting for 97.1%.In batch experiments,the maximum removal rates of COD,TP and TN in P.sp.SCSE709-6 treatment of saline black water were 96%,83%and 50%,respectively.In the semi-continuous experiment on board,the system T3 inoculated with P.sp.SCSE709-6 had the best COD removal rate(99.8%)and T3 and T4(two systems enhanced by P.sp.SCSE709-6 inoculation)had good phosphorus removal ability(removal rates were 80.9%and 88.4%,respectively).The unweighted UniFrac distance between T3 and T4 was the smallest(0.368).indicating the smallest community difference between T3 and T4.(2)Under cadmium stress,bacterial morphology became coarser and shorter.Phosphorus could alleviate the inhibition of cadmium on the growth of P.sp.SCSE709-6.The removal rate of cadmium by P.sp.SCSE709-6 increased with the increase of phosphorus concentration.The increase of phosphorus was beneficial to bacterial resistance to cadmium.The morphology of P.sp.SCSE709-6 in Cd-free wastewater with 9 mg/L phosphorus concentration was found to be slender rod-shaped,the length of bacteria was about 2 ?m and the width was about 1 ?m.With the increase of Cd concentration,the morphology of P.sp.SCSE709-6 became shorter and thicker,and some nanoparticles gathered around it.With the increase of phosphorus concentration,the effect of cadmium on bacterial morphology is reduced.Phosphorus can alleviate the inhibition of cadmium on bacterial growth.The pH value of wastewater first decreases and then increases to 7.5-8.4.P.sp.SCSE709-6 can adjust the pH of wastewater to weak alkalinity.With the increase of cadmium or phosphorus concentration,the content of proteoglycan in EPS increased gradually,and the increase of phosphorus was beneficial to the resistance of bacteria to cadmium.Three-dimensional fluorescence spectroscopy showed that with the increase of Cd or P concentration,the structure of aromatic proteins in EPS changed,humic acid peaks disappeared and new fulvic acid peaks appeared.The content of carboxyl group,carbonyl group,hydroxyl group and amino group of aromatic proteins increased,which resulted in the red shift of D peak.Thermogravimetric analysis showed that the increase of cadmium and phosphorus reduced the temperature of bacterial weight loss,increased the flammability of bacteria,and was conducive to the dehydration of bacteria after sewage treatment.With the increase of cadmium concentration,the removal rate of phosphorus and cadmium of P.sp.SCSE709-6 decreases;when cadmium concentration is 1-10 mg/L,the complete removal of phosphorus and cadmium can be achieved within 24 hours,and when cadmium concentration is more than 12 mg/L,the maximum removal rate of phosphorus and cadmium decreases.With the increase of phosphorus concentration,the removal rate of cadmium by P.sp.SCSE709-6 increased,which indicated that the presence of phosphorus was beneficial to the removal of cadmium by P.sp.SCSE709-6.(3)High cadmium can increase the exchangeable form of cadmium in bacteria,high phosphorus can reduce the total cadmium content in bacteria,make more cadmium accumulated in EPS and the exchangeable form of cadmium reduce the toxicity of cadmium;in wastewater containing cadmium,bacteria produce Cd-S-P nanoparticles.With the increase of time,phosphorus was transferred from EPS to intracellular,and intracellular cadmium increased first and then decreased.With the increase of phosphorus concentration,more phosphorus accumulated in EPS,and the main part of cadmium accumulation changed from cell membrane to EPS.The change of phosphorus and cadmium concentration did not change the main forms of phosphorus(monolipids,dilipids and orthophosphates).With the increase of cadmium concentration,the cadmium content in bacteria increased significantly,and the maximum increment of exchangeable cadmium and the direct toxicity of cadmium increased.With the increase of phosphorus concentration,the total cadmium content in bacteria decreased slightly,the exchangeable cadmium content decreased,and the reducible cadmium content increased,indicating that the direct toxicity of cadmium was reduced by phosphorus,and the form of cadmium changed from unstable to stable.When cadmium is contained in sewage,nanoparticles appear around bacteria,and the higher the concentration of cadmium,the more the particles aggregate.The extracted nanoparticles are aggregated and consist of many round particles with a diameter of about 30 nm.Their carbon content is high(87.8%).This indicates that the main organic matter in the nanoparticles is cadmium,sulfur and phosphorus,which account for 2.8%,2.9%and 0.2%respectively.When a circular particle in the aggregated nanoparticles is enlarged,it is found that it has obvious crystalline and amorphous properties.It consists of nanocrystals with a diameter of 2-3 nm,and the crystal plane spacing of the nanocrystals is 0.305 nm.By XPS,Cd3d fine spectra of nanoparticles showed that Cd mainly combined with sulfur and oxygen in Cd-S and O-Cd-O modes.The S2p spectra of EP S showed that it was mainly in the form of S2-and the P2p spectra showed that phosphorus mainly combined in the form of P043-,P-O-P.(4)Cadmium affects the direct uptake of phosphorus by bacteria.Cadmium can down-regulate inositol phosphoric acid metabolism and pentose phosphate pathway,and affect the activities of some enzymes in tricarboxylic acid cycle and glycolysis pathway,thus affecting the phosphorus metabolism of bacteria.GO-term,which was significantly enriched in differentially expressed genes,was mainly composed of extracellular membrane,external encapsulation structure,cell envelope,transmembrane transport of copper and silver ions,amino acid synthesis and metabolism,carboxylic acid biosynthesis and organic acid biosynthesis.KEGG analysis of differentially expressed genes showed that the differentially expressed genes were mainly enriched in arginine biosynthesis,biosynthesis of amino acids,cysteine and methionine metabolism,inositol phosphate metabolism under Cd stress.When the concentration of cadmium in sewage increased,the glutathione production increased slightly,and the activity of intracellular alkaline phosphatase increased.When phosphorus concentration increased,the concentration of glutathione decreased slightly,the activity of intracellular alkaline phosphatase decreased,and the available phosphorus of bacteria increased with the increase of phosphorus in the environment,without excessive decomposition of phosphorus stored in cells.The mechanism of cadmium resistance of P.sp.SCSE709-6 was clarified,(?)Inhibition of cadmium influx through down-regulation of cell membrane-related genes and adsorption of EPS;(?)up-regulation of sulfur-containing protein synthesis in cells,and combination of cadmium with sulfur-containing proteins and phosphorus-containing organics to achieve intracellular isolation and detoxification;(?)The up-regulation of RND transporter,lead/cadmium/zinc/mercury transporter ATPase,cobalt/zinc/cadmium resistant poteins CzcA,CzcB and CusA promotes cadmium ion effluxIn summary,P.sp.SCSE709-6 was applied to the treatment of phosphorus-containing wastewater to remove phosphorus and store phosphorus in bacteria in a biologically available form,which is of great significance for the reuse of phosphorus resources.The effects of different concentrations of phosphorus and cadmium on the physiological and biochemical properties of P.sp.SCSE709-6 and the removal efficiency of phosphorus and cadmium,as well as the migration of phosphorus and cadmium to P.sp.SCSE709-6 in the process of simultaneous removal of phosphorus and cadmium,provide a favorable theoretical basis and data support for the simultaneous removal of phosphorus and cadmium by The simultaneous removal of phosphorus and cadmium has achieved high efficiency and low cost removal of toxic and harmful pollutants,which has important environmental,ecological and economic benefits.In addition,exploring the biological mechanism of P.sp.SCSE709-6 under the action of phosphorus and cadmium is helpful to understand the correlation between phosphorus and cadmium in marine environment and phosphate rock,and to reveal the ecological significance of P.sp.SCSE709-6 in environment.