| Biomineralization is a common phenomenon in nature,and plays an important role in the geochemical cycle of elements.Compared with abiogenic mineralization,minerals produced by biomineralization usually possess unique composition,complex structure,and exquisite morphology,which reflect the regulation impact of organisms on mineral formation.As an orthorhombic phosphate mineral,struvite has been found in special geological environments such as guano deposits,marshes,and basalt caves.In vivo,struvite exists as a main component of infectious urinary stone,and its formation is closely related to urinary tract infection caused by urease-producing bacteria.Struvite is also a common scale in sewage treatment systems,and its deposits on the surface of equipments seriously affect the normal operation of sewage treatment plants.However,struvite contains three nutrients including nitrogen,phosphorus and magnesium,and can be used as an ideal slow-release fertilizer.Recently,crystallization and mineralization of struvite have attracted widespread attention including mineralogy,environmental and water treatment sciences,and biomedical sciences.In this dissertation,the ability of bacteria to mineralize struvite and the mineralogy of bio-struvite under different salinity conditions were firstly studied through the bacterial in situ mineralization method,and the effect of salinity on bacterial growth and struvite mineralization were ascertained.On this basis,the morphogenesis and evolution of struvite induced by the bacteria were systematically studied through the combination of bacterial in-situ mineralization and biomimetic mineralization techniques,and relevant regulation mechanisms were illuminated.At the same time,the effect of chiral biomolecules on struvite mineralization was systematically studied through the biomimetic synthesis method,and it was found that in the presence of chiral biomolecules,the change of solution chemistry led to the diversity of struvite chirality.The obtained results can not only expand and deepen the understanding of struvite biomineralization,but also provide an important biomineralogical guidance for the development of new technology to recover phosphorus source from wastewaters.Several important results of this dissertation were summarized as follows:1.Microbial mineralization of struvite is considered to be an effective way to reduce the cost of nitrogen and phosphorus removal and recovery from sewage.Seawater is rich in magnesium ions and in reserves,which can be used as a cheap magnesium source for struvite bio-recovery.However,high salinity in seawater may have potential effect on microbial growth and thus struvite biomineralization.To this end,a halophilic marine actinomycete,Microbacterium marinum sp.nov.H207 was selected as a model microbe to study the effect of salinity on its growth and struvite mineralization.The results showed that within the range of seawater salinity,the strain all grew well,and had good ability to remove phosphorus and mineralize struvite.However,the induction period for struvite precipitation increased with elevated salinity,and such retardation was due to the fact that high salinity stress was not conducive to the degradation of carbohydrates and nitrogenous organic compounds by this strain,thus delaying the increase in solution pH and supersaturation level.Meanwhile,the salinity can also affect the crystallization habits of bio-struvite.As the salinity increases,struvite crystals evolved from an arrowlike-shaped structure to tabular-shaped twinned structures consisting of trapezoidal individuals as well as tabular-shaped twin or single crystal structure that preferentially oriented along the crystallographic[100]direction.Current results have important biomineralogical guiding role for microbial struvite recovery process using seawater as magnesium source.2.The ability of bacteria to mineralize struvite and modify struvite habits has been well documented,but the limited work involving the biogenetic struvite morphogenesis and evolution obstructs the understanding of bacterially mediated struvite mineralization.Here,based on the aforementioned work,the Microbacterium marinum sp.nov.H207 was further chosen to study its effect on morphogenesis and evolution of struvite by using the combination of bacterial in situ mineralization and biomimetic mineralization techniques.The bacterial mineralization results showed that strain H207 could induce the formation of struvite grouping consisting of large trapezoid-like substrate structure and small coffin-like overgrowth structure,and the overgrowth structure gradually disappeared with time,while the substrate crystal further grew into coffin-like,and quadrangular tabular crystals.The biomimetic experiments with different organic components confirmed that the soluble and electronegative carboxyl groups-rich macromolecules secreted by strain H207 played a key role in the formation of the struvite grouping,and the time-course biomimetic experiments testified that the continuous increase in pH and NH4+ content caused by bacterial growth and metabolism led to the growth and morphological evolution of bio-struvite.Moreover,at the former stage,the substrate crystal grew along the crystallographic b axis,but the coupled dissolution-precipitation process occurred at the later stage,and the crystals grew along the[110]and[1-10]directions.Meanwhile,it was also found that the(00-1)face of substrate crystal preferentially dissolved,which results from the low initial phosphate content and high phosphate density on this face.As a result,present results have important mineralogical implication for the understanding of the morphogenesis and evolution of bio-struvite grouping structure.3.Biominerals with chiral morphologies are ubiquitous in marine and terrestrial organisms,and their formations are likely to be closely related to chiral biomolecules.In order to understand whether chiral molecule could induce the formation of struvite with chiral morphology,chiral tartaric acid was selected as a model biomolecule and its regulation on crystallization habits of struvite was studied.The results showed that in the presence of chiral tartaric acid,the chirality of struvite depended on the initial solution supersaturation,and high supersaturation conditions were favorable for the formation of chiral struvite.Controlled experiments with other chiral molecules showed that at relatively high supraturation,chiral malic acid can also induce the formation of chiral struvite,while struvite had no chiral characteristics under the action of nonchiral molecules such as acidic aspartic acid,neutral serine or alkaline histidine.Combined with the structure of these chiral biomolecules,it indicates that the hydroxyl and carboxyl groups attached to the chiral carbon atoms of the tartaric acid molecule should synergistically regulate the formation of chiral struvite.In addition,in the presence of homochiral tartaric acid,the chirality of struvite was different with the change of the initial solution chemistry.Given thatthe chiral diversity of natural chiral biominerals and the fact that bio molecules are often homochiral,the current results could provide a new perspective for the formation of different chiral biominerials in nature. |
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