Background:?Due to maternal and fetal physiologic demand, the rate along with amplitude of anemia is expected to rise over pregnancy. The iron and oxidative status also are expected to vary accordingly. It is thus ass...Background:?Due to maternal and fetal physiologic demand, the rate along with amplitude of anemia is expected to rise over pregnancy. The iron and oxidative status also are expected to vary accordingly. It is thus assumed that iron supplementation will somewhat modify the profile observed in markers of iron and oxidative status of our series. Objectives: We aimed to measure variations of indices of iron and oxidative status of iron supplemented women over pregnancy. Methods: This is a prospective observational cohort of 74 pregnant women with singleton pregnancy whose baseline iron and oxidative status have been recently assessed at University Clinics of Kinshasa, DR Congo. Women with anemia (Hb < 10 g%) took iron for curative purposes (320 mg/day of ferric ammonium citrate) while the others received preventive iron supplementation (160 mg/day). Iron was associated with 15 mg folate/day. Nutritional iron intake was measured through a 24-hour recall using a questionnaire of common foods, including stuffs and habits likely to impede iron absorption. Biological parameters of iron and oxidative status included hemoglobin, hematocrit, ferritin, serum iron, transferrin, superoxide dismutase or SOD, uric acid, oxidized LDL and blood glucose. For statistical calculations we used t-test, chi-square test, ANOVAR and regression, the significance being stated at p Results: Trimester wise evolution of hematologic status in anemic women shows a rise in values of hemoglobin (+average 1 gr/dl) and hematocrit (+3%) throughout pregnancy, with significant change only between recruitment and 28 - 32 weeks. In non anemic women a significant decrease was observed, although levels remained normal. For ferritin (7.5 - 53 ng/mL from recruitment to term) and transferrin (107 - 157 g/L), significant rise was found in anemic women from recruitment to 28 - 32 weeks, while in non anemic notable change occurred only for transferrin (133 - 204 g/L). Serum iron significantly increased (53 - 83 μg/dL) from recruitment to 28 - 32 weeks in anemic 展开更多
Background: Anemia during pregnancy is associated with oxidative stress, which might expectedly provoke harmful consequences on maternal and perinatal outcomes. Use of iron in women during pregnancy improves maternal ...Background: Anemia during pregnancy is associated with oxidative stress, which might expectedly provoke harmful consequences on maternal and perinatal outcomes. Use of iron in women during pregnancy improves maternal hematologic parameters, while likely to worsen oxidative status. Objectives: Our study thus aimed to assess adverse outcomes on all women having been routinely iron supplemented during pregnancy. Methods: This is a prospective observational cohort of 74 pregnant women with singleton pregnancy whose baseline iron and oxidative status along with variations throughout pregnancy have been recently assessed at university clinics of Kinshasa, DR Congo. Obstetrical adverse outcomes were assessed according to the diagnosis of anemia and oxidative stress considered at recruitment, at 28 - 32 weeks of gestation and at term. For statistical calculations, we used t-test, chi-square test, ANOVAR and regression, the significance being stated at p < 0.05. Results: Complications significantly associated with anemia at the beginning of pregnancy were acute fetal distress (OR = 3.9, p < 0.03), prematurity (OR = 7.3, p < 0.007), low birth weight or LBW (OR = 3.4, p < 0.05), birth asphyxia (OR = 15.1, p < 0.002) and neonatal hypoglycemia (OR = 3, p < 0.05). When the diagnosis of anemia was considered at 28 - 32 weeks of gestation, significant associations were found with gestational diabetes mellitus or GDM (OR = 3.8, p < 0.05), cesarean section (OR = 4.8, p < 0.003), prematurity (OR = 5.3, p < 0.03), birth asphyxia (OR = 10.9, p < 0.008) and neonatal hypoglycemia (OR = 4.7, p < 0.02). At term, the diagnosis of anemia was significantly associated with GDM (OR = 9.2, p < 0.01), premature rupture of membranes or PROM (OR = 2.8, p < 0.05), cesarean section (OR = 6.03, p < 0.01), birth asphyxia (OR = 2.9, p < 0.05) and neonatal hypoglycemia (OR = 3, p ?As of oxidative stress diagnosed at recruitment, significant associations were found with PROM (OR = 9, p < 0.02), cesarean section (OR = 3.7, p < 0.05), prematurity (OR = 6.展开更多
Corrosion and electrochemical behavior of 316L stainless steel was investigated in the presence of aerobic iron-oxidizing bacteria (IOB) and anaerobic sulfate-reducing bacteria (SRB) isolated from cooling water system...Corrosion and electrochemical behavior of 316L stainless steel was investigated in the presence of aerobic iron-oxidizing bacteria (IOB) and anaerobic sulfate-reducing bacteria (SRB) isolated from cooling water systems in an oil refinery using electrochemical measurement, scanning electron microscopy (SEM) and energy dispersive atom X-ray analysis(EDAX). The results show the corrosion potential and pitting potential of 316L stainless steel decrease distinctly in the presence of bacteria, in comparison with those observed in sterile medium under the same exposure time. SEM morphologies have shown that 316L stainless steel reveals no signs of pitting attack in the sterile medium. However, micrometer-scale corrosion pits were observed on 316L stainless steel surface in the presence of bacteria. The presence of SRB leads to higher corrosion rates than IOB. The interactions between the stainless steel surface, abiotic corrosion products, and bacterial cells and their metabolic products increased the corrosion damage degree of the passive film and accelerated pitting propagation.展开更多
The effect of hydraulic retention time (HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage (AMD) treatment was investigated.The simulated AMD was highly acidic (pH 2.5), rich in iron (...The effect of hydraulic retention time (HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage (AMD) treatment was investigated.The simulated AMD was highly acidic (pH 2.5), rich in iron (about 1700 mg/L) and copper (about 200 mg/L), and contained high concentrations of sulfate (about 4700 mg/L).The biooxidation of ferrous iron was studied in a laboratory-scale upflow packed bed bioreactor (PBR).The HRT was shortened stepwise from 40 h to 20 h, 13 h, and 8 h under the acidic environment at a pH value of 2.2.Then, the influent pH value was changed from 2.2 to 1.2 at a constant suitable HRT.Physiochemical and microbial community structure analyses were performed on water samples and stuffing collected from the bioreactor under different conditions.The results indicate that the efficiency of ferrous iron oxidation gradually decreased with the decrease of HRT, and when the HRT exceeded 13 h, ferrous iron in AMD was almost completely oxidized.In addition, the best efficiency of ferrous iron oxidation was achieved at the influent pH value of 1.8.Microbial community structure analyses show that Leptospirillum is the predominant genus attached in the bioreactor, and low influent pH values are suitable for the growth of Leptospirillum.展开更多
Extracellular polymeric substances(EPS)are an importantmedium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron(oxyhydr)oxides production wh...Extracellular polymeric substances(EPS)are an importantmedium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron(oxyhydr)oxides production which reduced arsenic(As)availability.The main component of EPS secreted by iron-oxidizing bacteria(Ochrobactrum EEELCW01)was composed of polysaccharides(150.76-165.33 mg/g DW)followed by considerably smaller amounts of proteins(12.98–16.12 mg/g DW).Low concentrations of As(100 or 500μmol/L)promoted the amount of EPS secretion.FTIR results showed that EPS was composed of polysaccharides,proteins,and a miniscule amount of nucleic acids.The functional groups including-COOH,-OH,-NH,-C=O,and-C-O played an important role in the adsorption of As.XPS results showed that As was bound to EPS in the form of As3+.With increasing As concentration,the proportion of As3+adsorbed on EPS increased.Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp.At day 8,the minerals were composed of goethite,galena,and siderite.With the increasing mineralization time,the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite(FeCO_(3))or goethite(α-FeOOH),and the specific surface area and active sites of minerals were reduced.It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals.This study is potential to understand the biomineralizationmechanism of iron-oxidizing bacteria and As remediation in the environment.展开更多
Iron-oxidizing strain(FeOB)and iron modified biochars have been shown arsenic(As)reme-diation ability in the environment.However,due to the complicated soil environment,few field experiment has been conducted.The stud...Iron-oxidizing strain(FeOB)and iron modified biochars have been shown arsenic(As)reme-diation ability in the environment.However,due to the complicated soil environment,few field experiment has been conducted.The study was conducted to investigate the potential of iron modified biochar(BC-FeOS)and biomineralization by a new found FeOB to remediate As-contaminated paddy field.Compared with the control,the As contents of G_(B)(BC-FeOS),G_(F)(FeOB),G_(FN)(FeOB and nitrogen fertilizer),G_(BF)(BC-FeOS and FeOB)and G_(BFN)(BC-FeOS,FeOB and nitrogen fertilizer)treatments in pore water decreased by 36.53%-80.03%and the microbial richness of iron-oxidizing bacteria in these treatments increased in soils at the rice maturation stage.The concentrations of available As of G_(B),G_(F),G_(FN),G_(BF) and G_(BFN) at the tillering stage were significantly decreased by 10.78%-55.48%.The concentrations of non-specifically absorbed and specifically absorbed As fractions of G_(B),G_(F),G_(FN),G_(BF) and G_(BFN) in soils were decreased and the amorphous and poorly crystalline hydrated Fe and Al oxidebound fraction was increased.Moreover,the As contents of G_(B),G_(F),G_(FN),G_(BF) and G_(BFN) in rice grains were significantly decreased(*P<0.05)and the total As contents of G_(FN),G_(BF) and G_(BFN) were lower than the standard limit of the National Standard for Food Safety(GB 2762-2017).Compared with the other treatments,G_(BFN) showed the greatest potential for the effective remediation of As-contaminated paddy fields.展开更多
Corrosion in drinking water distribution systems(DWDSs)may lead to pipe failures and water quality deterioration;biocorrosion is the most common type.Chlorine disinfectants are widely used in DWDSs to inhibit microorg...Corrosion in drinking water distribution systems(DWDSs)may lead to pipe failures and water quality deterioration;biocorrosion is the most common type.Chlorine disinfectants are widely used in DWDSs to inhibit microorganism growth,but these also promote electrochemical corrosion to a certain extent.This study explored the independent and synergistic effects of chlorine and microorganisms on pipeline corrosion.Sodium hypochlorite(NaOCl)at different concentrations(0,0.25,0.50,and 0.75 mg/L)and iron-oxidizing bacteria(IOB)were added to the reaction system,and a biofilm annular reactor(BAR)was employed to simulate operational water supply pipes and explain the composite effects.The degree of corrosion became severe with increasing NaOCl dosage.IOB accelerated the corrosion rate at an early stage,after which the reaction system gradually stabilized.When NaOCl and IOB existed together in the BAR,both synergistic and antagonistic effects occurred during the corrosion process.The AOC content increased due to the addition of NaOCl,which is conducive to bacterial regrowth.However,biofilm on cast iron coupons was greatly influenced by the disinfectant,leading to a decrease in microbial biomass over time.More research is needed to provide guidelines for pipeline corrosion control.展开更多
The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances （EPS） with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiologi...The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances （EPS） with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiological signatures. The Archean and early Palaeoproterozoic oceans were anoxic with high soluble Fe（Ⅱ） that were suggested to have been oxidized through the metabolism of Fe（II）-oxidizing bacteria. The precursor of the ultrafine hematite in banded iron formation （BIF）, e.g., ferrihy- drite, was suggested to be the mineral record of microbial Fe（Ⅱ）-oxidation at that time. However, both the biological materials and primary iron minerals were prone to being altered by diagenetic or low-grade metamorphic processes. This makes it diffi- cult to interpret the genesis of Precambrian BIFs. Here, we report experimental simulation on the effects of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe（Ⅱ）-oxidizing bacteria and their biomass. Stalks, sheaths, and iron oxide spheroidal aggregates are partially preserved after the 100 MPa/300℃ treatments, which indicates the mixed organic matters and iron oxides could survive the diagenetic or low-grade metamorphic processes. Some organic-mineral mixing structures carry information on microbial processes, though they appear similar to pseudomorphs of fossilized bacteria.展开更多
Corrosion and electrochemical behavior of 316L stainless steel was investigated in the presence of aerobic iron-oxidizing bacteria IOB and anaerobic sulfate-reducing bacteria SRB isolated from cooling water systems in...Corrosion and electrochemical behavior of 316L stainless steel was investigated in the presence of aerobic iron-oxidizing bacteria IOB and anaerobic sulfate-reducing bacteria SRB isolated from cooling water systems in an oil refinery using electrochemical measurement, scanning electron microscopy SEM and energy dispersive atom X-ray analysisEDAX. The results show the corrosion potential and pitting potential of 316L stainless steel decrease distinctly in the presence of bacteria, in comparison with those observed in sterile medium under the same exposure time. SEM morphologies have shown that 316L stainless steel reveals no signs of pitting attack in the sterile medium. However, micrometer-scale corrosion pits were observed on 316L stainless steel sur- face in the presence of bacteria. The presence of SRB leads to higher corrosion rates than IOB. The interactions between the stainless steel surface, abiotic corrosion products, and bacterial cells and their metabolic products in- creased the corrosion damage degree of the passive film and accelerated pitting propagation.展开更多
文摘Background:?Due to maternal and fetal physiologic demand, the rate along with amplitude of anemia is expected to rise over pregnancy. The iron and oxidative status also are expected to vary accordingly. It is thus assumed that iron supplementation will somewhat modify the profile observed in markers of iron and oxidative status of our series. Objectives: We aimed to measure variations of indices of iron and oxidative status of iron supplemented women over pregnancy. Methods: This is a prospective observational cohort of 74 pregnant women with singleton pregnancy whose baseline iron and oxidative status have been recently assessed at University Clinics of Kinshasa, DR Congo. Women with anemia (Hb < 10 g%) took iron for curative purposes (320 mg/day of ferric ammonium citrate) while the others received preventive iron supplementation (160 mg/day). Iron was associated with 15 mg folate/day. Nutritional iron intake was measured through a 24-hour recall using a questionnaire of common foods, including stuffs and habits likely to impede iron absorption. Biological parameters of iron and oxidative status included hemoglobin, hematocrit, ferritin, serum iron, transferrin, superoxide dismutase or SOD, uric acid, oxidized LDL and blood glucose. For statistical calculations we used t-test, chi-square test, ANOVAR and regression, the significance being stated at p Results: Trimester wise evolution of hematologic status in anemic women shows a rise in values of hemoglobin (+average 1 gr/dl) and hematocrit (+3%) throughout pregnancy, with significant change only between recruitment and 28 - 32 weeks. In non anemic women a significant decrease was observed, although levels remained normal. For ferritin (7.5 - 53 ng/mL from recruitment to term) and transferrin (107 - 157 g/L), significant rise was found in anemic women from recruitment to 28 - 32 weeks, while in non anemic notable change occurred only for transferrin (133 - 204 g/L). Serum iron significantly increased (53 - 83 μg/dL) from recruitment to 28 - 32 weeks in anemic
文摘Background: Anemia during pregnancy is associated with oxidative stress, which might expectedly provoke harmful consequences on maternal and perinatal outcomes. Use of iron in women during pregnancy improves maternal hematologic parameters, while likely to worsen oxidative status. Objectives: Our study thus aimed to assess adverse outcomes on all women having been routinely iron supplemented during pregnancy. Methods: This is a prospective observational cohort of 74 pregnant women with singleton pregnancy whose baseline iron and oxidative status along with variations throughout pregnancy have been recently assessed at university clinics of Kinshasa, DR Congo. Obstetrical adverse outcomes were assessed according to the diagnosis of anemia and oxidative stress considered at recruitment, at 28 - 32 weeks of gestation and at term. For statistical calculations, we used t-test, chi-square test, ANOVAR and regression, the significance being stated at p < 0.05. Results: Complications significantly associated with anemia at the beginning of pregnancy were acute fetal distress (OR = 3.9, p < 0.03), prematurity (OR = 7.3, p < 0.007), low birth weight or LBW (OR = 3.4, p < 0.05), birth asphyxia (OR = 15.1, p < 0.002) and neonatal hypoglycemia (OR = 3, p < 0.05). When the diagnosis of anemia was considered at 28 - 32 weeks of gestation, significant associations were found with gestational diabetes mellitus or GDM (OR = 3.8, p < 0.05), cesarean section (OR = 4.8, p < 0.003), prematurity (OR = 5.3, p < 0.03), birth asphyxia (OR = 10.9, p < 0.008) and neonatal hypoglycemia (OR = 4.7, p < 0.02). At term, the diagnosis of anemia was significantly associated with GDM (OR = 9.2, p < 0.01), premature rupture of membranes or PROM (OR = 2.8, p < 0.05), cesarean section (OR = 6.03, p < 0.01), birth asphyxia (OR = 2.9, p < 0.05) and neonatal hypoglycemia (OR = 3, p ?As of oxidative stress diagnosed at recruitment, significant associations were found with PROM (OR = 9, p < 0.02), cesarean section (OR = 3.7, p < 0.05), prematurity (OR = 6.
基金Supported by the National Natural Science Foundation of China (No.20576108).
文摘Corrosion and electrochemical behavior of 316L stainless steel was investigated in the presence of aerobic iron-oxidizing bacteria (IOB) and anaerobic sulfate-reducing bacteria (SRB) isolated from cooling water systems in an oil refinery using electrochemical measurement, scanning electron microscopy (SEM) and energy dispersive atom X-ray analysis(EDAX). The results show the corrosion potential and pitting potential of 316L stainless steel decrease distinctly in the presence of bacteria, in comparison with those observed in sterile medium under the same exposure time. SEM morphologies have shown that 316L stainless steel reveals no signs of pitting attack in the sterile medium. However, micrometer-scale corrosion pits were observed on 316L stainless steel surface in the presence of bacteria. The presence of SRB leads to higher corrosion rates than IOB. The interactions between the stainless steel surface, abiotic corrosion products, and bacterial cells and their metabolic products increased the corrosion damage degree of the passive film and accelerated pitting propagation.
基金supported by the National Natural Science Foundation of China(Grant No.U1402234)the Guangxi Scientific Research and Technology Development Plan(Grants No.GuikeAB16380287 and GuikeAB17129025)+2 种基金the Public Welfare Fund of the Ministry of Environmental Protection of China(Grant No.201509049)the Program of International S & T Cooperation(Grant No.2016YFE0130700)the Fund of the General Research Institute for Nonferrous Metals(Grants No.53321 and 53348)
文摘The effect of hydraulic retention time (HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage (AMD) treatment was investigated.The simulated AMD was highly acidic (pH 2.5), rich in iron (about 1700 mg/L) and copper (about 200 mg/L), and contained high concentrations of sulfate (about 4700 mg/L).The biooxidation of ferrous iron was studied in a laboratory-scale upflow packed bed bioreactor (PBR).The HRT was shortened stepwise from 40 h to 20 h, 13 h, and 8 h under the acidic environment at a pH value of 2.2.Then, the influent pH value was changed from 2.2 to 1.2 at a constant suitable HRT.Physiochemical and microbial community structure analyses were performed on water samples and stuffing collected from the bioreactor under different conditions.The results indicate that the efficiency of ferrous iron oxidation gradually decreased with the decrease of HRT, and when the HRT exceeded 13 h, ferrous iron in AMD was almost completely oxidized.In addition, the best efficiency of ferrous iron oxidation was achieved at the influent pH value of 1.8.Microbial community structure analyses show that Leptospirillum is the predominant genus attached in the bioreactor, and low influent pH values are suitable for the growth of Leptospirillum.
基金supported by the National Natural Science Foundation of China(No.42177392)the Dean’s Research Fund 2020/21(No.04626)of the Education University of Hong Kong.
文摘Extracellular polymeric substances(EPS)are an importantmedium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron(oxyhydr)oxides production which reduced arsenic(As)availability.The main component of EPS secreted by iron-oxidizing bacteria(Ochrobactrum EEELCW01)was composed of polysaccharides(150.76-165.33 mg/g DW)followed by considerably smaller amounts of proteins(12.98–16.12 mg/g DW).Low concentrations of As(100 or 500μmol/L)promoted the amount of EPS secretion.FTIR results showed that EPS was composed of polysaccharides,proteins,and a miniscule amount of nucleic acids.The functional groups including-COOH,-OH,-NH,-C=O,and-C-O played an important role in the adsorption of As.XPS results showed that As was bound to EPS in the form of As3+.With increasing As concentration,the proportion of As3+adsorbed on EPS increased.Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp.At day 8,the minerals were composed of goethite,galena,and siderite.With the increasing mineralization time,the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite(FeCO_(3))or goethite(α-FeOOH),and the specific surface area and active sites of minerals were reduced.It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals.This study is potential to understand the biomineralizationmechanism of iron-oxidizing bacteria and As remediation in the environment.
基金This work was supported by the National Natural Science Foundation of China(No.41771512)the Dean’s Research Fund 2020/21(Project code:04626)of the Education University of Hong Kong.
文摘Iron-oxidizing strain(FeOB)and iron modified biochars have been shown arsenic(As)reme-diation ability in the environment.However,due to the complicated soil environment,few field experiment has been conducted.The study was conducted to investigate the potential of iron modified biochar(BC-FeOS)and biomineralization by a new found FeOB to remediate As-contaminated paddy field.Compared with the control,the As contents of G_(B)(BC-FeOS),G_(F)(FeOB),G_(FN)(FeOB and nitrogen fertilizer),G_(BF)(BC-FeOS and FeOB)and G_(BFN)(BC-FeOS,FeOB and nitrogen fertilizer)treatments in pore water decreased by 36.53%-80.03%and the microbial richness of iron-oxidizing bacteria in these treatments increased in soils at the rice maturation stage.The concentrations of available As of G_(B),G_(F),G_(FN),G_(BF) and G_(BFN) at the tillering stage were significantly decreased by 10.78%-55.48%.The concentrations of non-specifically absorbed and specifically absorbed As fractions of G_(B),G_(F),G_(FN),G_(BF) and G_(BFN) in soils were decreased and the amorphous and poorly crystalline hydrated Fe and Al oxidebound fraction was increased.Moreover,the As contents of G_(B),G_(F),G_(FN),G_(BF) and G_(BFN) in rice grains were significantly decreased(*P<0.05)and the total As contents of G_(FN),G_(BF) and G_(BFN) were lower than the standard limit of the National Standard for Food Safety(GB 2762-2017).Compared with the other treatments,G_(BFN) showed the greatest potential for the effective remediation of As-contaminated paddy fields.
基金grateful for primary support from the National Natural Science Foundation of China(Grant No.51979194).
文摘Corrosion in drinking water distribution systems(DWDSs)may lead to pipe failures and water quality deterioration;biocorrosion is the most common type.Chlorine disinfectants are widely used in DWDSs to inhibit microorganism growth,but these also promote electrochemical corrosion to a certain extent.This study explored the independent and synergistic effects of chlorine and microorganisms on pipeline corrosion.Sodium hypochlorite(NaOCl)at different concentrations(0,0.25,0.50,and 0.75 mg/L)and iron-oxidizing bacteria(IOB)were added to the reaction system,and a biofilm annular reactor(BAR)was employed to simulate operational water supply pipes and explain the composite effects.The degree of corrosion became severe with increasing NaOCl dosage.IOB accelerated the corrosion rate at an early stage,after which the reaction system gradually stabilized.When NaOCl and IOB existed together in the BAR,both synergistic and antagonistic effects occurred during the corrosion process.The AOC content increased due to the addition of NaOCl,which is conducive to bacterial regrowth.However,biofilm on cast iron coupons was greatly influenced by the disinfectant,leading to a decrease in microbial biomass over time.More research is needed to provide guidelines for pipeline corrosion control.
基金supported by General Research Fund from Hong Kong Research Grants Council (Grant No. HKU703412)
文摘The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances （EPS） with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiological signatures. The Archean and early Palaeoproterozoic oceans were anoxic with high soluble Fe（Ⅱ） that were suggested to have been oxidized through the metabolism of Fe（II）-oxidizing bacteria. The precursor of the ultrafine hematite in banded iron formation （BIF）, e.g., ferrihy- drite, was suggested to be the mineral record of microbial Fe（Ⅱ）-oxidation at that time. However, both the biological materials and primary iron minerals were prone to being altered by diagenetic or low-grade metamorphic processes. This makes it diffi- cult to interpret the genesis of Precambrian BIFs. Here, we report experimental simulation on the effects of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe（Ⅱ）-oxidizing bacteria and their biomass. Stalks, sheaths, and iron oxide spheroidal aggregates are partially preserved after the 100 MPa/300℃ treatments, which indicates the mixed organic matters and iron oxides could survive the diagenetic or low-grade metamorphic processes. Some organic-mineral mixing structures carry information on microbial processes, though they appear similar to pseudomorphs of fossilized bacteria.
基金the National Natural Science Foundation of China (No.20576108).
文摘Corrosion and electrochemical behavior of 316L stainless steel was investigated in the presence of aerobic iron-oxidizing bacteria IOB and anaerobic sulfate-reducing bacteria SRB isolated from cooling water systems in an oil refinery using electrochemical measurement, scanning electron microscopy SEM and energy dispersive atom X-ray analysisEDAX. The results show the corrosion potential and pitting potential of 316L stainless steel decrease distinctly in the presence of bacteria, in comparison with those observed in sterile medium under the same exposure time. SEM morphologies have shown that 316L stainless steel reveals no signs of pitting attack in the sterile medium. However, micrometer-scale corrosion pits were observed on 316L stainless steel sur- face in the presence of bacteria. The presence of SRB leads to higher corrosion rates than IOB. The interactions between the stainless steel surface, abiotic corrosion products, and bacterial cells and their metabolic products in- creased the corrosion damage degree of the passive film and accelerated pitting propagation.
