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Díaz-Torres O, Lugo-Melchor OY, de Anda J, Orozco-Nunnelly DA, Gradilla-Hernández MS, Senés-Guerrero C. Characterizing a subtropical hypereutrophic lake: From physicochemical variables to shotgun metagenomic data. Front Microbiol 2022; 13:1037626. [DOI: 10.3389/fmicb.2022.1037626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Accepted: 10/31/2022] [Indexed: 12/05/2022] Open
Abstract
Lake Cajititlán is a subtropical and endorheic lake, which is heavily impacted by nutrient pollution. Agricultural runoff and poorly treated wastewater have entered this reservoir at alarming rates during past rainy seasons, causing the cultural eutrophication of this body of water and resulting in several massive fish kill events. In this study, shotgun metagenomic sequencing was used to examine the taxonomic and functional structure of microbial communities in Lake Cajititlán during the rainy season. Several water quality features and their interactions with microbial communities were also assessed to identify the major factors affecting the water quality and biota, specifically fish species. According to current water quality regulations, most of the physicochemical variables analyzed (dissolved oxygen, pH, Secchi disk, NH4+, NO3−, blue-green algae, total phosphorus, and chlorophyll-a) were outside of the permissible limits. Planktothrix agardhii and Microcystis aeruginosa were the most abundant phytoplankton species, and the dominant bacterial genera were Pseudomonas, Streptomyces, and Flavobacterium, with Pseudomonas fluorescens, Stenotrophomonas maltophilia, and Aeromonas veronii representing the most abundant bacterial species. All of these microorganisms have been reported to be potentially harmful to fish, and the latter three (P. fluorescens, S. maltophilia, A. veronii) also contain genes associated with pathogenicity in fish mortality (fur, luxS, aer, act, aha, exu, lip, ser). Genetic evidence from the microbial communities analyzed herein reveals that anthropogenic sources of nutrients in the lake altered genes involved in nitrogen, phosphorus, sulfur, and carbon metabolism, mainly at the beginning of the rainy season. These findings suggest that abiotic factors influence the structure of the microbial communities, along with the major biogeochemical cycles of Lake Cajititlán, resulting in temporal variations and an excess of microorganisms that can thrive in high-nutrient and low-oxygen environments. After reviewing the literature, this appears to be the first study that focuses on characterizing the water quality of a subtropical hypereutrophic lake through associations between physicochemical variables and shotgun metagenomic data. In addition, there are few studies that have coupled the metabolism of aquatic ecosystems with nutrient cycles.
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Chen L, Wang M, Li Y, Shang W, Tang J, Zhang Z, Liu F. Effects of Magnetic Minerals Exposure and Microbial Responses in Surface Sediment across the Bohai Sea. Microorganisms 2021; 10:microorganisms10010006. [PMID: 35056455 PMCID: PMC8778929 DOI: 10.3390/microorganisms10010006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 12/13/2021] [Accepted: 12/20/2021] [Indexed: 11/24/2022] Open
Abstract
Extensive production and application of magnetic minerals introduces significant amounts of magnetic wastes into the environment. Exposure to magnetic minerals could affect microbial community composition and geographic distribution. Here, we report that magnetic susceptibility is involved in determining bacterial α-diversity and community composition in surface sediment across the Bohai Sea by high-throughput sequencing analysis of the 16S rRNA gene. The results showed that environmental factors (explained 9.80%) played a larger role than spatial variables (explained 6.72%) in conditioning the bacterial community composition. Exposure to a magnetite center may shape the geographical distribution of five dissimilatory iron reducing bacteria. The microbial iron reduction ability and electroactive activity in sediment close to a magnetite center are stronger than those far away. Our study provides a novel understanding for the response of DIRB and electroactive bacteria to magnetic minerals exposure.
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Affiliation(s)
- Lei Chen
- School of Life Science, Qufu Normal University, Qufu 273165, China;
- Key Laboratory of Coastal Biology and Biological Resources Conversation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China; (W.S.); (J.T.)
| | - Mingpeng Wang
- School of Life Science, Qufu Normal University, Qufu 273165, China;
- Correspondence: (M.W.); (F.L.)
| | - Yuntao Li
- State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China;
| | - Weitao Shang
- Key Laboratory of Coastal Biology and Biological Resources Conversation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China; (W.S.); (J.T.)
| | - Jianhui Tang
- Key Laboratory of Coastal Biology and Biological Resources Conversation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China; (W.S.); (J.T.)
| | - Zhaojie Zhang
- Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA;
| | - Fanghua Liu
- Key Laboratory of Coastal Biology and Biological Resources Conversation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China; (W.S.); (J.T.)
- National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-Environmental Pollution Control and Management, Institute of Eco-Environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, China
- Correspondence: (M.W.); (F.L.)
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3
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Jeong Y, Hong SJ, Cho SH, Yoon S, Lee H, Choi HK, Kim DM, Lee CG, Cho S, Cho BK. Multi-Omic Analyses Reveal Habitat Adaptation of Marine Cyanobacterium Synechocystis sp. PCC 7338. Front Microbiol 2021; 12:667450. [PMID: 34054774 PMCID: PMC8155712 DOI: 10.3389/fmicb.2021.667450] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Accepted: 04/19/2021] [Indexed: 11/13/2022] Open
Abstract
Cyanobacteria are considered as promising microbial cell factories producing a wide array of bio-products. Among them, Synechocystis sp. PCC 7338 has the advantage of growing in seawater, rather than requiring arable land or freshwater. Nonetheless, how this marine cyanobacterium grows under the high salt stress condition remains unknown. Here, we determined its complete genome sequence with the embedded regulatory elements and analyzed the transcriptional changes in response to a high-salt environment. Complete genome sequencing revealed a 3.70 mega base pair genome and three plasmids with a total of 3,589 genes annotated. Differential RNA-seq and Term-seq data aligned to the complete genome provided genome-wide information on genetic regulatory elements, including promoters, ribosome-binding sites, 5'- and 3'-untranslated regions, and terminators. Comparison with freshwater Synechocystis species revealed Synechocystis sp. PCC 7338 genome encodes additional genes, whose functions are related to ion channels to facilitate the adaptation to high salt and high osmotic pressure. Furthermore, a ferric uptake regulator binding motif was found in regulatory regions of various genes including SigF and the genes involved in energy metabolism, suggesting the iron-regulatory network is connected to not only the iron acquisition, but also response to high salt stress and photosynthesis. In addition, the transcriptomics analysis demonstrated a cyclic electron transport through photosystem I was actively used by the strain to satisfy the demand for ATP under high-salt environment. Our comprehensive analyses provide pivotal information to elucidate the genomic functions and regulations in Synechocystis sp. PCC 7338.
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Affiliation(s)
- Yujin Jeong
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
| | - Seong-Joo Hong
- Department of Biological Engineering, Inha University, Incheon, South Korea.,Department of Biological Sciences and Bioengineering, Inha University, Incheon, South Korea
| | - Sang-Hyeok Cho
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
| | - Seonghoon Yoon
- Department of Biological Engineering, Inha University, Incheon, South Korea.,Department of Biological Sciences and Bioengineering, Inha University, Incheon, South Korea
| | - Hookeun Lee
- Institute of Pharmaceutical Research, College of Pharmacy, Gachon University, Incheon, South Korea
| | | | - Dong-Myung Kim
- Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon, South Korea
| | - Choul-Gyun Lee
- Department of Biological Engineering, Inha University, Incheon, South Korea.,Department of Biological Sciences and Bioengineering, Inha University, Incheon, South Korea
| | - Suhyung Cho
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.,Innovative Biomaterials Center, KI for the BioCentury, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
| | - Byung-Kwan Cho
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.,Innovative Biomaterials Center, KI for the BioCentury, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.,Intelligent Synthetic Biology Center, Daejeon, South Korea
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4
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Addison EL, Gerlach KT, Spellman CD, Santilli G, Fairbrother AR, Shepard Z, Dudle JD, Goodwill JE. Physicochemical implications of cyanobacteria oxidation with Fe(VI). CHEMOSPHERE 2021; 266:128956. [PMID: 33218732 DOI: 10.1016/j.chemosphere.2020.128956] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Revised: 10/16/2020] [Accepted: 11/10/2020] [Indexed: 06/11/2023]
Abstract
Increases in harmful algal blooms has negatively impacted many surface-sourced drinking water utilities. To control these blooms, many water utilities implement pre-oxidation with ozone, chlorine, or permanganate; however, pre-oxidation of algae has both positive and negative water quality outcomes. This study investigated ferrate (Fe(VI)) as an alternative oxidant by measuring its effect on cell lysing, surface characteristics, and coagulation in waters containing the cyanobacteria Microcystis aeruginosa. Bench scale studies were conducted to examine the complex combination of processes in a Fe(VI)-algae system. These processes were characterized by fluorescence index, surface charge, collision frequency modeling, particle counts and sphericity, total nitrogen, and ferrate decomposition measurements. Results showed that Fe(VI) lysed algal cells, but further oxidation of released organic matter is possible. The presence of algae did not significantly impact the rate of Fe(VI) decomposition. Fe(VI) pre-oxidation may also be capable of decreasing the formation of nitrogenated disinfection byproducts through subsequent oxidation of released nitrogen rich organic matter. Streaming current and zeta potential results indicate destabilization of the resulting algae and iron suspension was incomplete under most conditions. Particle collision frequency modeling indicates fluid shear to be an important aggregation mechanism of the resulting suspension. Overall, Fe(VI) is a viable alternative to other strong oxidants for water utilities struggling with harmful algal blooms, but the final fate of the resulting organic matter must be further studied.
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Affiliation(s)
- Erika L Addison
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, 02881, USA
| | - Kyle T Gerlach
- Department of Civil and Environmental Engineering, Worcester Polytechnic Institute, Worcester, MA, 01609, USA
| | - Charles D Spellman
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, 02881, USA
| | - Grace Santilli
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, 02881, USA
| | - Alyson R Fairbrother
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, 02881, USA; Tighe & Bond, 300 West Exchange Street, Providence, RI, 02903, USA
| | - Zachary Shepard
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, 02881, USA
| | - Jeanine D Dudle
- Department of Civil and Environmental Engineering, Worcester Polytechnic Institute, Worcester, MA, 01609, USA
| | - Joseph E Goodwill
- Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, RI, 02881, USA.
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5
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Lee J, Kim M, Jeong SE, Park HY, Jeon CO, Park W. Amentoflavone, a novel cyanobacterial killing agent from Selaginella tamariscina. JOURNAL OF HAZARDOUS MATERIALS 2020; 384:121312. [PMID: 31699478 DOI: 10.1016/j.jhazmat.2019.121312] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Revised: 09/23/2019] [Accepted: 09/23/2019] [Indexed: 05/10/2023]
Abstract
Harmful cyanobacterial bloom (HCB) by Microcystis aeruginosa is increasingly becoming a serious concern to the environment and human health alike. Currently, many physical, chemical, and biological controls are underway to eliminate HCB, but natural chemicals are rarely used. To find a control agent with low environmental toxicity and high potential for practical use, 60 plant extracts were screened. Only Selaginella tamariscina extract killed all four Microcystis aeruginosa strains, but not the other tested bacteria. Chloroform fraction of S. tamariscina extract (CSE) showed the highest killing activity. The effects of CSE on M. aeruginosa were monitored using differential interference contrast microscopy and flow-cytometry analysis, scanning electron microscopy, and transmission electron microscopy. The images showed that CSE-treated cells were abnormally altered, with damaged cell membranes, peptidoglycan layers, and cytoplasm. Quadrupole time-of-flight liquid chromatography-mass spectrometry was used to identify amentoflavone as a major active compound. Pure amentoflavone, even at low concentrations showed a powerful killing effect on M. aeruginosa, but not on other non-cyanobacteria. Overall, in this study, we have highlighted the potentials of S. tamariscina extracts and amentoflavone as selective HCB control agents.
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Affiliation(s)
- Jaebok Lee
- Laboratory of Molecular Environmental Microbiology, Department of Environmental Science and Ecological Engineering, Korea University, Seoul, 02841, Republic of Korea
| | - Minkyung Kim
- Laboratory of Molecular Environmental Microbiology, Department of Environmental Science and Ecological Engineering, Korea University, Seoul, 02841, Republic of Korea
| | - Sang Eun Jeong
- Department of Life Science, Chung-Ang University, Seoul, 06974, Republic of Korea
| | - Hye Yoon Park
- National Institute of Biological Resources, Incheon, 22689, Republic of Korea
| | - Che Ok Jeon
- Department of Life Science, Chung-Ang University, Seoul, 06974, Republic of Korea
| | - Woojun Park
- Laboratory of Molecular Environmental Microbiology, Department of Environmental Science and Ecological Engineering, Korea University, Seoul, 02841, Republic of Korea.
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6
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Qiu Y, Wang Z, Huang Z, Liu F, Tang D, Liu J. Effect of four kinds of complexing iron on the process of iron uptake by Anabaena flos-aquae. MICROBIOLOGY-SGM 2020; 166:359-366. [PMID: 32022661 DOI: 10.1099/mic.0.000891] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
AbstractIron (Fe), which is a necessary micronutrient for algal growth, plays an important role in the physiological metabolism and enzymatic reactions of algae. This study aimed to investigate the absorption process of four kinds of complexing iron absorbed by Anabaena flos-aquae. Results showed that the absorptive capacity of A. flos-aquae to complex iron was inversely proportional to the stability of the complex bond of complex iron. Complex iron with weak binding ability can be quickly adsorbed by A. flos-aquae. The absorptive rate was as follows: ferric humate, ferric oxalate >ammonium ferric citrate >EDTA Fe. For EDTA-Fe with a strong binding ability, a moderate iron concentration (e.g. 0.6 mg l-1) is favourable for iron uptake by A. flos-aquae. Our experiments also revealed that the process of separating iron from complex iron before entering algal cells was probably as follows: iron complexed with organic ligands were firstly adsorbed on the surface of algae cells; afterwards, iron ions were captured by organic matter on the surface of algae cells, accompanied by the rupture of the bond between Fe3+ and ligand; finally, the Fe3+ entered into the cell of algae while the organic ligands returned to the medium.
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Affiliation(s)
- Yongting Qiu
- School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, PR China
| | | | - Ziqi Huang
- School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Feng Liu
- School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Daijun Tang
- School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, PR China
| | - Junxia Liu
- School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, PR China
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7
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Effects of Light Intensity and Exposure Period on the Growth and Stress Responses of Two Cyanobacteria Species: Pseudanabaena galeata and Microcystis aeruginosa. WATER 2020. [DOI: 10.3390/w12020407] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Light is an important factor that affects cyanobacterial growth and changes in light can influence their growth and physiology. However, an information gap exists regarding light-induced oxidative stress and the species-specific behavior of cyanobacteria under various light levels. This study was conducted to evaluate the comparative effects of different light intensities on the growth and stress responses of two cyanobacteria species, Pseudanabaena galeata (strain NIES 512) and Microcystis aeruginosa (strain NIES 111), after periods of two and eight days. The cyanobacterial cultures were grown under the following different light intensities: 0, 10, 30, 50, 100, 300, and 600 μmol m−2 s−1. The optical density (OD730), chlorophyll a (Chl-a) content, protein content, H2O2 content, and the antioxidative enzyme activities of catalase (CAT) and peroxidase (POD) were measured separately in each cyanobacteria species. P. galeata was negatively affected by light intensities lower than 30 μmol m−2 s−1 and higher than 50 μmol m−2 s−1. A range of 30 to 50 μmol m−2 s−1 light was favorable for the growth of P. galeata, whereas M. aeruginosa had a higher tolerance for extreme light conditions. The favorable range for M. aeruginosa was 10 to 100 μmol m−2 s−1.
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8
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Fu QL, Fujii M, Natsuike M, Waite TD. Iron uptake by bloom-forming freshwater cyanobacterium Microcystis aeruginosa in natural and effluent waters. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2019; 247:392-400. [PMID: 30690235 DOI: 10.1016/j.envpol.2019.01.071] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Revised: 01/08/2019] [Accepted: 01/20/2019] [Indexed: 06/09/2023]
Abstract
Studies on Fe uptake by phytoplankton have been often conducted using artificial culture media. However, Fe chemistry in freshwater can be influenced by riverine anthropogenic impacts and other factors causing water quality changes. In this study, therefore, Fe uptake in natural (river and reservoir) and effluent waters was investigated for the notorious bloom-forming freshwater cyanobacterium Microcystis aeruginosa. To investigate the Fe uptake mechanism, a short-term incubational assay was conducted in the presence of light, Fe(II) ligand and Fe(III) reductant, with results consistently indicating that unchelated Fe(III) is the major substrate for Fe uptake by M. aeruginosa. Further assays using various freshwater samples indicated that Fe uptake is lower in natural waters compared to that of effluent waters and, interestingly, Fe uptake was found to be limited in natural waters. These results suggest that Fe limitation can be alleviated by the inflow of effluent waters. Statistical analysis with various water quality variables indicated that Fe availability is significantly influenced by concentrations of dissolved Fe and organic matter as well as specific UV absorbance (an index of aromaticity). Overall, findings of this study highlight that watershed anthropogenic activities exert important roles in Fe uptake by freshwater cyanobacteria via alteration of Fe speciation.
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Affiliation(s)
- Qing-Long Fu
- Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Ookayama, Tokyo, Japan.
| | - Manabu Fujii
- Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Ookayama, Tokyo, Japan.
| | - Masafumi Natsuike
- Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Ookayama, Tokyo, Japan
| | - T David Waite
- School of Civil and Environmental Engineering, The University of New South Wales, Sydney, Australia
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Fu Q, Yeung ACY, Fujii M, Neilan BA, Waite TD. Physiological responses of the freshwater N
2
‐fixing cyanobacterium
Raphidiopsis raciborskii
to Fe and N availabilities. Environ Microbiol 2019; 21:1211-1223. [DOI: 10.1111/1462-2920.14545] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 01/23/2019] [Accepted: 01/24/2019] [Indexed: 12/12/2022]
Affiliation(s)
- Qing‐Long Fu
- Department of Civil and Environmental Engineering Tokyo Institute of Technology Ookayama, Tokyo Japan
| | - Anna C. Y. Yeung
- School of Civil and Environmental Engineering The University of New South Wales Sydney Australia
| | - Manabu Fujii
- Department of Civil and Environmental Engineering Tokyo Institute of Technology Ookayama, Tokyo Japan
| | - Brett A. Neilan
- School of Environmental and Life Sciences The University of Newcastle Newcastle Australia
| | - T. David Waite
- School of Civil and Environmental Engineering The University of New South Wales Sydney Australia
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10
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Takaara T, Sasaki S, Fujii M, Ito H, Masago Y, Omura T. Lectin-stimulated cellular iron uptake and toxin generation in the freshwater cyanobacterium Microcystis aeruginosa. HARMFUL ALGAE 2019; 83:25-33. [PMID: 31097253 DOI: 10.1016/j.hal.2019.01.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Revised: 12/11/2018] [Accepted: 01/08/2019] [Indexed: 06/09/2023]
Abstract
The lectin family is composed of mono- and oligosaccharide binding proteins that could activate specific cellular activities, such as cell-cell attachment and toxin production. In the present study, the effect of the external addition of lectins to culture media containing the freshwater cyanobacterium Microcystis aeruginosa on its metabolic activities, such as iron uptake and toxin production was investigated. Among the three lectins examined in this study (concanavalin A [Con A], wheat germ agglutinin [WGA] and peanut agglutinin [PNA]), PNA substantially increased the accumulated intracellular and extracellular iron content. The binding of PNA and Con A to M. aeruginosa cells was visualized via fluorescence microscopy using a lectin adjunct with fluorescein isothiocyanate, and resulted in carbohydrate and protein accumulation in the cellular capsule. Given that the highest carbohydrate accumulation was seen in the Con A system (where iron accumulation was relatively lower), carbohydrate quality is likely important factor that influences cellular iron accumulation. Since PNA specifically binds to sugars such as galactose and N-acetylgalactosamine, these saccharide species could be important candidates for intracellular and extracellular iron accumulation and transport. Microcystin biosynthesis was stimulated in the presence of PNA and WGA, whereas cellular iron uptake increased only in the presence of PNA. Thus, the iron uptake was not necessarily congruent with the upregulation of microcystin synthesis, which suggested that the positive effect of lectin on iron uptake is probably attributable to the PNA-assisted iron accumulation around the cell surface. Overall, the present study provides insights into the interactions of lectin that influence cellular metabolic activities such as iron uptake, extracellular polymeric substance accumulation, and toxin production.
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Affiliation(s)
- Tomoko Takaara
- Department of Civil and Environmental Engineering, National Institute of Technology, Fukushima College, Japan
| | - Shiori Sasaki
- New Industry Creation Hatchery Center, Tohoku University, Japan
| | - Manabu Fujii
- Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Japan.
| | - Hiroaki Ito
- Center for Water Cycle, Marine Environment and Disaster Management, Kumamoto University, Japan
| | - Yoshifumi Masago
- Institute for the Advanced Study of Sustainability, United Nation University, Japan
| | - Tatsuo Omura
- New Industry Creation Hatchery Center, Tohoku University, Japan
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11
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Facciponte DN, Bough MW, Seidler D, Carroll JL, Ashare A, Andrew AS, Tsongalis GJ, Vaickus LJ, Henegan PL, Butt TH, Stommel EW. Identifying aerosolized cyanobacteria in the human respiratory tract: A proposed mechanism for cyanotoxin-associated diseases. THE SCIENCE OF THE TOTAL ENVIRONMENT 2018; 645:1003-1013. [PMID: 30248825 PMCID: PMC6159226 DOI: 10.1016/j.scitotenv.2018.07.226] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Revised: 07/12/2018] [Accepted: 07/17/2018] [Indexed: 05/10/2023]
Abstract
Cyanobacteria produce harmful toxins that have been associated with several acute conditions and chronic human diseases, like gastroenteritis, non-alcoholic liver disease, and amyotrophic lateral sclerosis. Aerosol from waterbodies appears to be a likely mechanism for exposure. We conducted a study of human biospecimens focused on the cyanobacterial aerosilization process by evaluating the extent to which cyanobacteria can invade the human respiratory tract. Our study suggests that humans routinely inhale aerosolized cyanobacteria, which can be harbored in the nostrils and the lungs. Using PCR, cyanobacteria were found at high frequencies in the upper respiratory tract (92.20%) and central airway (79.31%) of our study subjects. Nasal swabs were not predictive of bronchoalveolar lavage (BAL) when detecting inhaled cyanobacteria. Interestingly, we found no evidence that time of year was a significant factor for cyanobacteria positivity (BAL cytology p = 1.0 and PCR p = 1.0); (nasal swab cytology p = 0.051 and PCR p = 0.65). Additionally, we found that proximity to a waterbody was not a significant factor for cyanobacteria positivity in BAL and nasal swabs collected during cyanobacteria bloom season [May-October] (p = 0.46 and p = 0.38). These data suggest that cyanobacteria exposure may be a prevalent and chronic phenomenon not necessarily restricted to waterbodies alone. Sources of indoor exposure warrant future investigation. Given the widespread prevalence of cyanobacterial exposure in the airway, investigation of the aerosol spread of cyanotoxins, more specifically, is warranted. Our findings are consistent with the hypothesis that aerosol is a significant route for cyanobacteria exposure, and thus a likely route of transmission for cyanotoxin-associated human diseases.
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Affiliation(s)
- Dominic N Facciponte
- Dartmouth-Hitchcock Medical Center, Department of Neurology, One Medical Center Dr., Lebanon, NH 03756, USA.
| | - Matthew W Bough
- Dartmouth-Hitchcock Medical Center, Department of Neurology, One Medical Center Dr., Lebanon, NH 03756, USA; Dartmouth College, Hanover, NH 03755, USA
| | - Darius Seidler
- Dartmouth-Hitchcock Medical Center, Department of Pulmonary and Critical Care Medicine, One Medical Center Dr., Lebanon, NH 03756, USA; Geisel School of Medicine at Dartmouth, One Rope Ferry Rd., Hanover, NH 03755, USA
| | - James L Carroll
- Dartmouth-Hitchcock Medical Center, Department of Pulmonary and Critical Care Medicine, One Medical Center Dr., Lebanon, NH 03756, USA; Geisel School of Medicine at Dartmouth, One Rope Ferry Rd., Hanover, NH 03755, USA
| | - Alix Ashare
- Dartmouth-Hitchcock Medical Center, Department of Pulmonary and Critical Care Medicine, One Medical Center Dr., Lebanon, NH 03756, USA; Geisel School of Medicine at Dartmouth, One Rope Ferry Rd., Hanover, NH 03755, USA
| | - Angeline S Andrew
- Dartmouth-Hitchcock Medical Center, Department of Neurology, One Medical Center Dr., Lebanon, NH 03756, USA; Geisel School of Medicine at Dartmouth, One Rope Ferry Rd., Hanover, NH 03755, USA
| | - Gregory J Tsongalis
- Dartmouth-Hitchcock Medical Center, Department of Pathology and Laboratory Medicine, One Medical Center Dr., Lebanon, NH 03756, USA; Geisel School of Medicine at Dartmouth, One Rope Ferry Rd., Hanover, NH 03755, USA
| | - Louis J Vaickus
- Dartmouth-Hitchcock Medical Center, Department of Pathology and Laboratory Medicine, One Medical Center Dr., Lebanon, NH 03756, USA; Geisel School of Medicine at Dartmouth, One Rope Ferry Rd., Hanover, NH 03755, USA
| | - Patricia L Henegan
- Dartmouth-Hitchcock Medical Center, Department of Neurology, One Medical Center Dr., Lebanon, NH 03756, USA
| | - Tanya H Butt
- Dartmouth-Hitchcock Medical Center, Department of Neurology, One Medical Center Dr., Lebanon, NH 03756, USA
| | - Elijah W Stommel
- Dartmouth-Hitchcock Medical Center, Department of Neurology, One Medical Center Dr., Lebanon, NH 03756, USA; Geisel School of Medicine at Dartmouth, One Rope Ferry Rd., Hanover, NH 03755, USA.
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12
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Lee D, Kwon M, Ahn Y, Jung Y, Nam SN, Choi IH, Kang JW. Characteristics of intracellular algogenic organic matter and its reactivity with hydroxyl radicals. WATER RESEARCH 2018; 144:13-25. [PMID: 30005177 DOI: 10.1016/j.watres.2018.06.069] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Revised: 06/26/2018] [Accepted: 06/29/2018] [Indexed: 06/08/2023]
Abstract
The aim of this study was to investigate the reactivity of intracellular algogenic organic matter (IOM) with hydroxyl radicals (·OH), a key reaction species in advanced oxidation processes. IOM was extracted from two green algae, Chlamydomonas reinhardtii and Scenedesmus sp., and two blue-green algae, Anabaena sp. and Microcystis aeruginosa using a freeze-thaw method. The second-order rate constants of the extracted IOM with ·OH were determined as 7.95 × 108 MC-1 s-1 (Chlamydomonas reinhardtii), 6.71 × 108 MC-1 s-1 (Scenedesmus sp.), 4.02 × 108 MC-1 s-1 (Anabaena sp.), and 4.45 × 108 MC-1 s-1 (Microcystis aeruginosa). These rate constants were significantly higher than values reported for dissolved organic matter in various water sources. This implies that IOM formation during algal bloom season could change the ·OH water matrix demand and adversely affect the performance of advanced oxidation processes. To investigate the physical and chemical composition characteristics of IOM and their relationship to the rate constants determined for the reaction between IOM and ·OH, liquid chromatography-organic carbon detection (LC-OCD) and fluorescence excitation-emission matrix & parallel factor analysis (FEEM-PARAFAC) were used. The IOM mainly consisted of low molecular weight (LMW) matter and protein-related compounds, as evidenced LMW neutrals (38-65%), biopolymers (7-19%), and tryptophan-like compounds (74-94%). Based on the composition characteristics of IOM, it was concluded that the molecular weight and the presence of nitrogen-containing compounds are influential parameters for determining the reactivity of IOM with ·OH.
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Affiliation(s)
- Doorae Lee
- Department of Environmental Engineering (YIEST), Yonsei University, 234 Maeji, Heungup, Wonju 220-710, Republic of Korea
| | - Minhwan Kwon
- Department of Environmental Engineering (YIEST), Yonsei University, 234 Maeji, Heungup, Wonju 220-710, Republic of Korea
| | - Yongtae Ahn
- Department of Environmental Engineering (YIEST), Yonsei University, 234 Maeji, Heungup, Wonju 220-710, Republic of Korea
| | - Youmi Jung
- Department of Environmental Engineering (YIEST), Yonsei University, 234 Maeji, Heungup, Wonju 220-710, Republic of Korea
| | - Seong-Nam Nam
- Department of Civil and Environmental Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul, 06974, Republic of Korea
| | - Il-Hwan Choi
- Water Analysis and Research Center, Korea Water Resources Corporation, 200 Sintanjin-ro, Daedeok-gu, Daejeon, 34350, Republic of Korea
| | - Joon-Wun Kang
- Department of Environmental Engineering (YIEST), Yonsei University, 234 Maeji, Heungup, Wonju 220-710, Republic of Korea.
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Relationship between Photosynthetic Capacity and Microcystin Production in Toxic Microcystis Aeruginosa under Different Iron Regimes. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2018; 15:ijerph15091954. [PMID: 30205471 PMCID: PMC6163392 DOI: 10.3390/ijerph15091954] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 08/25/2018] [Accepted: 09/05/2018] [Indexed: 11/17/2022]
Abstract
Blooms of harmful cyanobacteria have been observed in various water bodies across the world and some of them can produce intracellular toxins, such as microcystins (MCs), which negatively impact aquatic organisms and human health. Iron participates significantly in cyanobacterial photosynthesis and is proposed to be linked to MC production. Here, the cyanobacteria Microcystis aeruginosa was cultivated under different iron regimes to investigate the relationship between photosynthetic capacity and MC production. The results showed that iron addition increased cell density, cellular protein concentration and the Chl-a (chlorophyll-a) content. Similarly, it can also up⁻regulate photosynthetic capacity and promote MC⁻leucine⁻arginine (MC⁻LR) production, but not in a dose⁻dependent manner. Moreover, a significant positive correlation between photosynthetic capacity and MC production was observed, and electron transport parameters were the most important parameters contributing to the variation of intracellular MC⁻LR concentration revealed by Generalized Additive Model analysis. As the electron transport chain was affected by iron variation, adenosine triphosphate production was inhibited, leading to the alteration of MC synthetase gene expression. Therefore, it is demonstrated that MC production greatly relies on redox status and energy metabolism of photosynthesis in M. aeruginosa. In consequence, more attention should be paid to the involvement of photosynthesis in the regulation of MC production by iron variation in the future.
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15
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Farid MU, Jeong S, Seo DH, Ahmed R, Lau C, Gali NK, Ning Z, An AK. Mechanistic insight into the in vitro toxicity of graphene oxide against biofilm forming bacteria using laser-induced breakdown spectroscopy. NANOSCALE 2018; 10:4475-4487. [PMID: 29459912 DOI: 10.1039/c8nr00189h] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
While the cytotoxicity of graphene oxide (GO) has been well established, its bactericidal mechanism, however, has yet to be elucidated to advance GO-based biomedical and environmental applications. In an attempt to better understand the bactericidal action of GO, herein we studied the interactions of GO with Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus cells using physical techniques and chemical probes, respectively. In particular, a novel laser-induced breakdown spectroscopy (LIBS) based elemental fingerprint analysis revealed notable differences between viable and non-viable cells based on the difference in the concentration of trace inorganic elements in complex bacterial systems, which reflect cellular membrane integrity. Lower emission intensities from essential inorganic ions in the GO-treated cells offered explicit evidence on the efflux of intracellular molecules from the bacteria through damaged cell membranes. Furthermore, a detailed structural and morphological investigation of bacterial membrane integrity confirmed GO-induced membrane stress upon direct contact interactions with bacterial cells, resulting in the disruption of cellular membranes. Moreover, the generation of intracellular reactive oxygen species (ROS) in the presence of an added antioxidant underlined the role of GO-mediated oxidative stress in bacterial cell inactivation. Thus, by correlating the changes in the bacterial elemental compositions with the severe morphological alterations and the high ROS production witnessed herein, we propose that the bactericidal mechanism of GO is likely to be the synergy between membrane and oxidative stress towards both tested species. Our findings offer useful guidelines for the future development of GO-based antibacterial surfaces and coatings.
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Affiliation(s)
- Muhammad Usman Farid
- School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong Special Administrative Region, China.
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Wang C, Wang X, Wang P, Chen B, Hou J, Qian J, Yang Y. Effects of iron on growth, antioxidant enzyme activity, bound extracellular polymeric substances and microcystin production of Microcystis aeruginosa FACHB-905. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2016; 132:231-239. [PMID: 27337497 DOI: 10.1016/j.ecoenv.2016.06.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Revised: 06/07/2016] [Accepted: 06/07/2016] [Indexed: 06/06/2023]
Abstract
Toxic cyanobacterial blooms have occurred in various water bodies during recent decades and made serious health hazards to plants, animals and humans. Iron is an important micronutrient for algal growth and recently, the concentration of which has increased remarkably in freshwaters. In this paper, the cyanobacterium Microcystis aeruginosa FACHB-905 was cultivated under non-iron (0μM), iron-limited (10μM) and iron-replete (100μM) conditions to investigate the effects of iron on growth, antioxidant enzyme activity, EPS and microcystin production. The results showed that algal cell density and chlorophyll-a content were maximal at the highest iron concentration. Antioxidant enzymes activity increased notably under all three conditions in the early stage of experiment, of which the SOD activity recovered soon from oxidative stress in 10μM group. The productions of some protein-like substances and humic acid-like substances of bound EPS were inhibited in iron-containing groups in the early stage of experiment while promoted after the adaptation period of Microcystis aeruginosa. Iron addition is a factor affecting the formation of cyanobacterial blooms through its impact on the content of LB-EPS and the composition of TB-EPS. The intracellular MC-LR concentration and the productivity potential of MC-LR were the lowest in 0μM group and highest in 10μM group. No obvious extracellular release of MC-LR was observed during the cultivation time. Therefore, iron addition can promote the physiological activities of M. aeruginosa, but a greater harm could be brought into environment under iron-limited (10μM) condition than under iron-replete (100μM) condition.
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Affiliation(s)
- Chao Wang
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, No. 1 Xikang Road, Nanjing 210098, China
| | - Xun Wang
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, No. 1 Xikang Road, Nanjing 210098, China
| | - Peifang Wang
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, No. 1 Xikang Road, Nanjing 210098, China.
| | - Bin Chen
- School of Environment, Beijing Normal University, No. 19 Xinjiekouwai Street, Beijing 100875, China
| | - Jun Hou
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, No. 1 Xikang Road, Nanjing 210098, China
| | - Jin Qian
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, No. 1 Xikang Road, Nanjing 210098, China
| | - Yangyang Yang
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, No. 1 Xikang Road, Nanjing 210098, China
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Physiological and Proteomic Responses of Continuous Cultures of Microcystis aeruginosa PCC 7806 to Changes in Iron Bioavailability and Growth Rate. Appl Environ Microbiol 2016; 82:5918-29. [PMID: 27474713 DOI: 10.1128/aem.01207-16] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 07/24/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The hepatotoxin microcystin (MCYST) is produced by a variety of freshwater cyanobacterial species, including Microcystis aeruginosa Interestingly, MCYST-producing M. aeruginosa strains have been shown to outcompete their nontoxic counterparts under iron-limiting conditions. However, the reasons for this are unclear. Here we examined the proteomic response of M. aeruginosa PCC 7806 continuous cultures under different iron and growth regimes. Iron limitation was correlated with a global reduction in levels of proteins associated with energy metabolism and photosynthesis. These proteomic changes were consistent with physiological observations, including reduced chlorophyll a content and reduced cell size. While levels of MCYST biosynthesis proteins did not fluctuate during the study period, both intra- and extracellular toxin quotas were significantly higher under iron-limiting conditions. Our results support the hypothesis that intracellular MCYST plays a role in protecting the cell against oxidative stress. Further, we propose that extracellular MCYST may act as a signaling molecule, stimulating MCYST production under conditions of iron limitation and enhancing the fitness of bloom populations. IMPORTANCE Microcystin production in water supply reservoirs is a global public health problem. Understanding the ecophysiology of hepatotoxic cyanobacteria, including their responses to the presence of key micronutrient metals such as iron, is central to managing harmful blooms. To our knowledge, this was the first study to examine proteomic and physiological changes occurring in M. aeruginosa continuous cultures under conditions of iron limitation at different growth rates.
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18
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Continuous cultivation of photosynthetic microorganisms: Approaches, applications and future trends. Biotechnol Adv 2015; 33:1228-45. [DOI: 10.1016/j.biotechadv.2015.03.004] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 02/26/2015] [Accepted: 03/06/2015] [Indexed: 12/30/2022]
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Fujii M, Yeung ACY, Waite TD. Competitive Effects of Calcium and Magnesium Ions on the Photochemical Transformation and Associated Cellular Uptake of Iron by the Freshwater Cyanobacterial Phytoplankton Microcystis aeruginosa. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:9133-42. [PMID: 26132788 DOI: 10.1021/acs.est.5b01583] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Photochemical reduction of iron and iron uptake by Microcystis were investigated in a freshwater medium (pH 8) containing a range of calcium (Ca) and magnesium (Mg) ion concentrations (0.002-20 mM). In a medium containing the chelator ethylenediaminetetraacetic acid (EDTA), 50-fold increases in net photochemical formation rates of unchelated ferrous iron (Fe(II)') were observed as the concentration of calcium or magnesium metal (Me) was increased to exceed the concentration of EDTA. Kinetic modeling of iron transformation processes indicated that the facilitated Fe(II)' formation is attributed to Me-promoted photoreductive dissociation of the ferric iron-EDTA complex. In the medium containing Suwanee River fulvic acid, in contrast, the competitive effect of Me on photochemical Fe(II)' formation appears to be negligible due to the weak binding affinities of fulvic acid to Me. The cellular iron uptake rate in the EDTA-buffered system increased by ∼3-fold in the excess Me condition where the increased rate of photochemical Fe(II)' formation was observed, whereas the presence of Me resulted in a decrease in iron uptake rate in the fulvic acid system (by up to 5-fold). The decrease in iron uptake is likely caused by Me binding to iron transporters and other entities involved in intracellular iron transport. The findings of this study indicate a significant effect of Ca and Mg concentrations in natural waters on iron uptake by Microcystis, with the magnitude of effect depending strongly on ligand type.
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Affiliation(s)
- Manabu Fujii
- †Department of Civil Engineering, Tokyo Institute of Technology, 2-12-1-M1-4 Ookayama, Tokyo 152-8552, Japan
| | - Anna C Y Yeung
- ‡School of Civil and Environmental Engineering, The University of New South Wales, Sydney, NSW 2052, Australia
| | - T David Waite
- ‡School of Civil and Environmental Engineering, The University of New South Wales, Sydney, NSW 2052, Australia
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Alexova R, Dang TC, Fujii M, Raftery MJ, Waite TD, Ferrari BC, Neilan BA. Specific global responses to N and Fe nutrition in toxic and non-toxicMicrocystis aeruginosa. Environ Microbiol 2015; 18:401-13. [DOI: 10.1111/1462-2920.12958] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 06/05/2015] [Accepted: 06/15/2015] [Indexed: 01/03/2023]
Affiliation(s)
- Ralitza Alexova
- School of Biotechnology and Biomolecular Sciences; University of New South Wales; Sydney NSW 2052 Australia
| | - The Cuong Dang
- School of Civil and Environmental Engineering; University of New South Wales; Sydney NSW 2052 Australia
| | - Manabu Fujii
- School of Civil and Environmental Engineering; University of New South Wales; Sydney NSW 2052 Australia
- Department of Civil Engineering; Tokyo Institute of Technology; 2-12-1-M1-4 Ookayama Tokyo 152-8552 Japan
| | - Mark J. Raftery
- Bioanalytical Mass Spectrometry Facility; University of New South Wales; Sydney NSW 2052 Australia
| | - T. David Waite
- School of Civil and Environmental Engineering; University of New South Wales; Sydney NSW 2052 Australia
| | - Belinda C. Ferrari
- School of Biotechnology and Biomolecular Sciences; University of New South Wales; Sydney NSW 2052 Australia
- Australian Centre for Astrobiology; University of New South Wales; Sydney NSW 2052 Australia
| | - Brett A. Neilan
- School of Biotechnology and Biomolecular Sciences; University of New South Wales; Sydney NSW 2052 Australia
- Australian Centre for Astrobiology; University of New South Wales; Sydney NSW 2052 Australia
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21
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Fujii M, Dang TC, Bligh MW, Rose AL, Waite TD. Effect of natural organic matter on iron uptake by the freshwater cyanobacterium Microcystis aeruginosa. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 48:365-374. [PMID: 24261844 DOI: 10.1021/es404090h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The mode of Fe uptake by the cyanobacterium Microcystis aeruginosa cultured in Fraquil* (pH 8) containing Suwannee River fulvic acid (SRFA) was examined using short-term radiolabeled (55)Fe uptake assays and a kinetic model that describes extracellular Fe transformations. Both Fe(II) and Fe(III) uptake rates decreased substantially with increasing SRFA concentration as the availability of unchelated Fe decreased due to complexation by SRFA. Fe uptake rates under illuminated conditions were comparable to or slightly higher than those observed in the dark at the same Fe:SRFA concentration ratio, in contrast to results for systems containing ethylenediaminetetraacetic acid where Fe uptake rates were much greater under illumination than in the dark. The limited effect of light principally resulted from the relatively high rates of thermal dissociation and dark reduction of Fe(III) bound to SRFA and complexation of photogenerated Fe(II) by SRFA. Our findings imply that Fe uptake by M. aeruginosa at a fixed total Fe concentration of 200 nM is close to saturation when fulvic acid is present at concentrations near those typically found in natural waters (< ∼5 mg·L(-1)), with cellular growth likely to be limited by Fe availability only when natural organic matter is present at very high concentrations (>25 mg·L(-1)).
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Affiliation(s)
- M Fujii
- Department of Civil Engineering, Tokyo Institute of Technology , 2-12-1-M1-4 Ookayama, Tokyo, Japan
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