Likai Hao - Academia.edu (original) (raw)

Papers by Likai Hao

FEMS Microbiology Ecology, 2014

Anoxygenic phototrophic Fe(II)-oxidizing bacteria (photoferrotrophs) are suggested to have contri... more Anoxygenic phototrophic Fe(II)-oxidizing bacteria (photoferrotrophs) are suggested to have contributed to the deposition of banded iron formations (BIFs) from oxygen-poor seawater. However, most studies evaluating the contribution of photoferrotrophs to Precambrian Fe(II) oxidation have used freshwater and not marine strains. Therefore, we investigated the physiology and mineral products of Fe(II) oxidation by the marine photoferrotroph Rhodovulum iodosum. Poorly crystalline Fe(III) minerals formed initially and transformed to more crystalline goethite over time. During Fe(II) oxidation, cell surfaces were largely free of minerals. Instead, the minerals were co-localized with EPS suggesting that EPS plays a critical role in preventing cell encrustation, likely by binding Fe (III) and directing precipitation away from cell surfaces. Fe(II) oxidation rates increased with increasing initial Fe(II) concentration (0.43-4.07 mM) under a light intensity of 12 lmol quanta m À2 s À1. Rates also increased as light intensity increased (from 3 to 20 lmol quanta m À2 s À1), while the addition of Si did not significantly change Fe(II) oxidation rates. These results elaborate on how the physical and chemical conditions present in the Precambrian ocean controlled the activity of marine photoferrotrophs and confirm the possibility that such microorganisms could have oxidized Fe(II), generating the primary Fe(III) minerals that were then deposited to some Precambrian BIFs.

Applied and Environmental Microbiology, 2013

Biofilms, organic matter, iron/aluminum oxides, and clay minerals bind toxic heavy metal ions and... more Biofilms, organic matter, iron/aluminum oxides, and clay minerals bind toxic heavy metal ions and control their fate and bioavailability in the environment. The spatial relationship of metal ions to biomacromolecules such as extracellular polymeric substances (EPS) in biofilms with microbial cells and biogenic minerals is complex and occurs at the micro- and submicrometer scale. Here, we review the application of highly selective and sensitive metal fluorescent probes for confocal laser scanning microscopy (CLSM) that were originally developed for use in life sciences and propose their suitability as a powerful tool for mapping heavy metals in environmental biofilms and cell-EPS-mineral aggregates (CEMAs). The benefit of using metal fluorescent dyes in combination with CLSM imaging over other techniques such as electron microscopy is that environmental samples can be analyzed in their natural hydrated state, avoiding artifacts such as aggregation from drying that is necessary for an...

Microscopy and Microanalysis, 2014

Chemical nano-tomography of microbial cells in their natural, hydrated state provides direct evid... more Chemical nano-tomography of microbial cells in their natural, hydrated state provides direct evidence of metabolic and chemical processes. Cells of the nitrate-reducing Acidovorax sp. strain BoFeN1 were cultured in the presence of ferrous iron. Bacterial reduction of nitrate causes precipitation of Fe(III)-(oxyhydr)oxides in the periplasm and in direct vicinity of the cells. Nanoliter aliquots of cell-suspension were injected into custom-designed sample holders wherein polyimide membranes collapse around the cells by capillary forces. The immobilized, hydrated cells were analyzed by synchrotron-based scanning transmission X-ray microscopy in combination with angle-scan tomography. This approach provides three-dimensional (3D) maps of the chemical species in the sample by employing their intrinsic near-edge X-ray absorption properties. The cells were scanned through the focus of a monochromatic soft X-ray beam at different, chemically specific X-ray energies to acquire projection ima...

Environmental Microbiology

Geochimica et Cosmochimica Acta

Minerals

The phase transformation of iron minerals induced by aqueous Fe(II) (Fe(II)aq) is a critical geoc... more The phase transformation of iron minerals induced by aqueous Fe(II) (Fe(II)aq) is a critical geochemical reaction which greatly affects the geochemical behavior of soil elements. How the geochemical behavior of rare earth elements (REEs) is affected by the Fe(II)aq-induced phase transformation of iron minerals, however, is still unknown. The present study investigated the adsorption and immobilization of REEs during the Fe(II)aq-induced phase transformation of ferrihydrite. The results show that the heavy REEs of Ho(III) were more efficiently adsorbed and stabilized compared with the light REEs of La(III) by ferrihydrite and its transformation products, which was due to the higher adsorptive affinity and smaller atomic radius of Ho(III). Both La(III) and Ho(III) inhibited the Fe atom exchange between Fe(II)aq and ferrihydrite, and sequentially, the Fe(II)aq-induced phase transformation rates of ferrihydrite, because of the competitive adsorption with Fe(II)aq on the surface of iron ...

Analytical Chemistry

A broad-spectrum fluorescent probe, which can be applied to monitoring H2S in various biological ... more A broad-spectrum fluorescent probe, which can be applied to monitoring H2S in various biological systems, has been rationally designed and synthesized. This specific probe was applied to localize the endogenous H2S in living Raw264.7 macrophage cells, HepG2 cells, and H9C2 cells. At the same time, the probe has successfully visualized CBS- and CSE-induced endogenous H2S production and monitored CBS and CSE activity in H9C2 cells. This probe could serve as a powerful molecular imaging tool to further explore the physiological function and the molecular mechanisms of endogenous H2S in living animal systems.

Scientific reports, Aug 3, 2016

A series of Cu(2+) probe which contains 9 probes have been synthesized and established. All the p... more A series of Cu(2+) probe which contains 9 probes have been synthesized and established. All the probes were synthesized using Rhodamine B as the fluorophore, conjugated to various differently substituted cinnamyl aldehyde with C=N Schiff base structural motif as their core moiety. The structure-property relationships of these probes have been investigated. The change of optical properties, caused by different electronic effect and steric effect of the recognition group, has been analyzed systematically. DFT calculation simulation of the Ring-Close and Ring-Open form of all the probes have been employed to illuminate, summarize and confirm these correlations between optical properties and molecular structures. In addition, biological experiment demonstrated that all the probes have a high potential for both sensitive and selective detection, mapping of adsorbed Cu(2+) both in vivo and environmental microbial systems. This approach provides a significant strategy for studying structur...

Environmental science & technology, Jan 9, 2015

Fe(II)-oxidizing bacteria form biogenic cell-mineral aggregates (CMAs) composed of microbial cell... more Fe(II)-oxidizing bacteria form biogenic cell-mineral aggregates (CMAs) composed of microbial cells, extracellular organic compounds, and ferric iron minerals. CMAs are capable of immobilizing large quantities of heavy metals, such as nickel, via sorption processes. CMAs play an important role for the fate of heavy metals in the environment, particularly in systems characterized by elevated concentrations of dissolved metals, such as mine drainage or contaminated sediments. We applied scanning transmission (soft) X-ray microscopy (STXM) spectrotomography for detailed 3D chemical mapping of nickel sorbed to CMAs on the submicron scale. We analyzed different CMAs produced by phototrophic or nitrate-reducing microbial Fe(II) oxidation and, in addition, a twisted stalk structure obtained from an environmental biofilm. Nickel showed a heterogeneous distribution and was found to be preferentially sorbed to biogenically precipitated iron minerals such as Fe(III)-(oxyhydr)oxides and, to a mi...

Frontiers in Earth Science, 2015

Evidence for Fe(II) oxidation and deposition of Fe(III)-bearing minerals from anoxic or redox-str... more Evidence for Fe(II) oxidation and deposition of Fe(III)-bearing minerals from anoxic or redox-stratified Precambrian oceans has received support from decades of sedimentological and geochemical investigation of Banded Iron Formations (BIF). While the exact mechanisms of Fe(II) oxidation remains equivocal, reaction with O 2 in the marine water column, produced by cyanobacteria or early oxygenic phototrophs, was likely. In order to understand the role of cyanobacteria in the deposition of Fe(III) minerals to BIF, we must first know how planktonic marine cyanobacteria respond to ferruginous (anoxic and Fe(II)-rich) waters in terms of growth, Fe uptake and homeostasis, and Fe mineral formation. We therefore grew the common marine cyanobacterium Synechococcus PCC 7002 in closed bottles that began anoxic, and contained Fe(II) concentrations that span the range of possible concentrations in Precambrian seawater. These results, along with cell suspension experiments, indicate that Fe(II) is likely oxidized by this strain via chemical oxidation with oxygen produced during photosynthesis, and not via any direct enzymatic or photosynthetic pathway. Imaging of the cell-mineral aggregates with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) are consistent with extracellular precipitation of Fe(III) (oxyhydr)oxide minerals, but that >10% of Fe(III) sorbs to cell surfaces rather than precipitating. Proteomic experiments support the role of reactive oxygen species (ROS) in Fe(II) toxicity to Synechococcus PCC 7002. The proteome expressed under low Fe conditions included multiple siderophore biosynthesis and siderophore and Fe transporter proteins, but most siderophores are not expressed during growth with Fe(II). These results provide a mechanistic and quantitative framework for evaluating the geochemical consequences of perhaps life's greatest metabolic innovation, i.e., the evolution and activity of oxygenic photosynthesis, in ferruginous Precambrian oceans.

Analytica chimica acta, Jan 8, 2015

A novel, solvent-dependent "off-on" probe with benzoylthiourea moiety as the functional... more A novel, solvent-dependent "off-on" probe with benzoylthiourea moiety as the functional receptor and fluorescein as the fluorophore was designed for monitoring of Ag(+) in EtOH-H2O (2:8, v/v) solution and Zn(2+) in CH3CN-H2O (2:8, v/v) solution at physiological range with sufficient selectivity and sensitivity. The Ag(+) promoted desulfurization of thiosemicarbazide functionality in formation of the 1,3,4-oxadiazole and the coordination of Zn(2+) to the O atom and N atom of the spoirolactam moiety and the S atom of the benzoylthiourea moiety were investigated to be the power that promoted the fluorescent enhancement. This probe was tested highly suitable for mapping Ag(+) and Zn(2+) in living human osteosarcoma MG-63 cells and microbial cell-EPS-mineral aggregates, thus, providing a wonderful candidate for tracking Ag(+) and Zn(2+) in biological organisms and processes.

ABSTRACT Two novel fluorescein-based OCl− chemosensors were designed, synthesized and characteriz... more ABSTRACT Two novel fluorescein-based OCl− chemosensors were designed, synthesized and characterized. Both fluorescence probes utilize an irreversible OCl-–promoted oxidation reaction to trigger the activation of fluorescence. These probes were shown to be highly selective for OCl-, and showed real time responses as well as a positive linear relationship to OCl− concentrations. The probes were successfully applied for the detection of OCl− in tap water and for fluorescence imaging of OCl− in bacterial Rhodobacter ferrooxidans sp. strain SW2 cell-EPS-mineral aggregates.

Journal of Microscopy, 2014

We present ScatterJ, an ImageJ plugin that allows for extracting qualitative as well as quantitat... more We present ScatterJ, an ImageJ plugin that allows for extracting qualitative as well as quantitative information from analytical microscopy datasets. A large variety of analytical microscopy methods are used to obtain spatially resolved chemical information. The resulting datasets are often large and complex, and can contain information that is not obvious or directly accessible. ScatterJ extends and complements existing methods to extract information on correlation and colocalization from pairs of species-specific or element-specific maps. We demonstrate the possibilities to extract information using example datasets from biogeochemical studies, although the plugin is not restricted to this type of research. The information that we could extract from our existing data helped to further our understanding of biogeochemical processes such as mineral formation or heavy metal sorption. ScatterJ can be used for a variety of different two-dimensional (2D) and three-dimensional (3D) datasets such as energy-dispersive X-ray spectroscopy maps, 3D confocal laser scanning microscopy maps, and 2D scanning transmission X-ray microscopy maps.

Geobiology, 2014

The formation of cell-(iron)mineral aggregates as a consequence of bacterial iron oxidation is an... more The formation of cell-(iron)mineral aggregates as a consequence of bacterial iron oxidation is an environmentally widespread process with a number of implications for processes such as sorption and coprecipitation of contaminants and nutrients. Whereas the overall appearance of such aggregates is easily accessible using 2-D microscopy techniques, the 3-D and internal structure remain obscure. In this study, we examined the 3-D structure of cell-(iron)mineral aggregates formed during Fe(II) oxidation by the nitrate-reducing Acidovorax sp. strain BoFeN1 using a combination of advanced 3-D microscopy techniques. We obtained 3-D structural and chemical information on different cellular encrustation patterns at high spatial resolution (4-200 nm, depending on the method): more specifically, (1) cells free of iron minerals, (2) periplasm filled with iron minerals, (3) spike- or platelet-shaped iron mineral structures, (4) bulky structures on the cell surface, (5) extracellular iron mineral...

Geochimica et Cosmochimica Acta, 2016

Aggregates consisting of bacterial cells, extracellular polymeric substances (EPS) and Fe(III) mi... more Aggregates consisting of bacterial cells, extracellular polymeric substances (EPS) and Fe(III) minerals formed by Fe(II)-oxidizing bacteria are common at bulk or microscale chemical interfaces where Fe cycling occurs. The high sorption capacity and binding capacity of cells, EPS, and minerals controls the mobility and fate of heavy metals. However, it remains unclear to which of these component(s) the metals will bind in complex aggregates. To clarify this question, the present study focuses on 3D mapping of heavy metals sorbed to cells, glycoconjugates that comprise the majority of EPS constituents, and Fe(III) mineral aggregates formed by the phototrophic Fe(II)oxidizing bacteria Rhodobacter ferrooxidans SW2 using confocal laser scanning microscopy (CLSM) in combination with metal-and glycoconjugates-specific fluorophores. The present study evaluated the influence of glycoconjugates, microbial cell surfaces, and (biogenic) Fe(III) minerals, and the availability of ferrous and ferric iron on heavy metal sorption. Analyses in this study provide detailed knowledge on the spatial distribution of metal ions in the aggregates at the sub-µm scale, which is essential to understand the underlying mechanisms of microbe-mineral-metal interactions. The heavy metals (Au 3+ , Cd 2+ , Cr 3+ , CrO 4 2-, Cu 2+ , Hg 2+ , Ni 2+ , Pd 2+ , tributyltin (TBT) and Zn 2+) were found mainly sorbed to cell surfaces, present within the glycoconjugates matrix, and bound to the mineral surfaces, but not incorporated into the biogenic Fe(III) minerals. Statistical analysis revealed that all ten heavy metals tested showed relatively similar sorption behaviour that was affected by the presence of sorbed ferrous and ferric iron. Results in this study showed that in addition to the mineral surfaces, both bacterial cell surfaces and the glycoconjugates provided most of sorption sites for heavy metals. Simultaneously, ferrous and ferric iron ions competed 3 with the heavy metals for sorption sites on the organic compounds. In summary, the information obtained by the present approach using a microbial model system provides important information to better understand the interactions between heavy metals and biofilms, and microbially formed Fe(III) minerals and heavy metals in complex natural environments.