Catherine J. Edward, Mariette Smart, Athanasios Kotsiopoulos, Susan T.L. Harrison
{"title":"Sulfur oxidation kinetics of Acidithiobacillus caldus and its inhibition on exposure to thiocyanate present in cyanidation tailings wastewater","authors":"Catherine J. Edward, Mariette Smart, Athanasios Kotsiopoulos, Susan T.L. Harrison","doi":"10.1016/j.resmic.2023.104134","DOIUrl":null,"url":null,"abstract":"<div><p>The sulfur oxidation kinetics of an industrial strain of <em>Acidithiobacillus caldus</em> (<em>At. caldus</em>) cultured on elemental sulfur was explored in batch experiments in the absence and presence of thiocyanate (SCN<sup>−</sup>), a toxin inherent within cyanidation tailings wastewater. The Contois rate expression accurately described <em>At. caldus</em> sulfate generation (R<sup>2</sup> > 0.93) and microbial growth (R<sup>2</sup> > 0.87). For a culture maintained at 45 °C a maximum specific growth rate (<span><math><mrow><msub><mi>μ</mi><mi>max</mi></msub></mrow></math></span>) of 0.105 h<sup>−1</sup>, sulfate yield from biomass (<span><math><mrow><msub><mi>Y</mi><mrow><mi>p</mi><mi>x</mi></mrow></msub></mrow></math></span>) of 4.8 × 10<sup>−9</sup> mg SO<sub>4</sub><sup>2−</sup>.cell<sup>−1</sup>, and Contois affinity coefficient (<span><math><mrow><msub><mi>K</mi><mi>x</mi></msub></mrow></math></span>) of 1.56 × 10<sup>−8</sup> mg S.cell<sup>−1</sup> were established. The presence of SCN<sup>−</sup> (0 mg/L - 20 mg/L) in the bulk solution inhibited the microbial system competitively. Moreover, SCN<sup>−</sup> impeded microbial growth differentially; the rate expression was therefore partitioned with respect to SCN<sup>−</sup> concentration and inhibition constants (<span><math><mrow><msub><mi>K</mi><mi>i</mi></msub></mrow></math></span>) were determined for each region. Adaptation to discrete concentrations of SCN<sup>−</sup> (1 mg/L and 20 mg/L) improved SCN<sup>−</sup> tolerance in <em>At. caldus</em>; however, adapted strains exhibited reduced sulfur oxidation potential when cultured under thiocyanate-free conditions relative to the non-adapted control strain. To describe the adapted systems accurately, the Contois affinity coefficient (<span><math><mrow><msub><mi>K</mi><mi>x</mi></msub></mrow></math></span>) was revised to reflect the suspected metabolic decline. The derived <span><math><mrow><msub><mi>K</mi><mi>x</mi></msub></mrow></math></span> values increased in magnitude and affirmed an innate reduction in microbial substrate affinity or substrate adsorption capacity. Inclusion of these updated <span><math><mrow><msub><mi>K</mi><mi>x</mi></msub></mrow></math></span> constants within the rate equation suitably represented the experimental data for both adapted <em>At. caldus</em> strains with R<sup>2</sup> > 0.94. Furthermore, the impact of adaptation on the inhibition kinetics and inhibition mechanism associated with SCN<sup>−</sup> exposure were reviewed. Thiocyanate inhibited sulfur oxidation non-competitively in the adapted strains, and the shift in inhibition mechanism may be attributed to the compromised metabolic state following adaptation.</p></div>","PeriodicalId":2,"journal":{"name":"ACS Applied Bio Materials","volume":null,"pages":null},"PeriodicalIF":4.6000,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0923250823001092/pdfft?md5=ab5d0b7bfee4b9d888a6bd7e62bea358&pid=1-s2.0-S0923250823001092-main.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Applied Bio Materials","FirstCategoryId":"99","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0923250823001092","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATERIALS SCIENCE, BIOMATERIALS","Score":null,"Total":0}
引用次数: 0
Abstract
The sulfur oxidation kinetics of an industrial strain of Acidithiobacillus caldus (At. caldus) cultured on elemental sulfur was explored in batch experiments in the absence and presence of thiocyanate (SCN−), a toxin inherent within cyanidation tailings wastewater. The Contois rate expression accurately described At. caldus sulfate generation (R2 > 0.93) and microbial growth (R2 > 0.87). For a culture maintained at 45 °C a maximum specific growth rate () of 0.105 h−1, sulfate yield from biomass () of 4.8 × 10−9 mg SO42−.cell−1, and Contois affinity coefficient () of 1.56 × 10−8 mg S.cell−1 were established. The presence of SCN− (0 mg/L - 20 mg/L) in the bulk solution inhibited the microbial system competitively. Moreover, SCN− impeded microbial growth differentially; the rate expression was therefore partitioned with respect to SCN− concentration and inhibition constants () were determined for each region. Adaptation to discrete concentrations of SCN− (1 mg/L and 20 mg/L) improved SCN− tolerance in At. caldus; however, adapted strains exhibited reduced sulfur oxidation potential when cultured under thiocyanate-free conditions relative to the non-adapted control strain. To describe the adapted systems accurately, the Contois affinity coefficient () was revised to reflect the suspected metabolic decline. The derived values increased in magnitude and affirmed an innate reduction in microbial substrate affinity or substrate adsorption capacity. Inclusion of these updated constants within the rate equation suitably represented the experimental data for both adapted At. caldus strains with R2 > 0.94. Furthermore, the impact of adaptation on the inhibition kinetics and inhibition mechanism associated with SCN− exposure were reviewed. Thiocyanate inhibited sulfur oxidation non-competitively in the adapted strains, and the shift in inhibition mechanism may be attributed to the compromised metabolic state following adaptation.
在氰化尾矿废水中固有毒素硫氰酸盐(SCN-)不存在和存在的情况下,对在元素硫上培养的工业酸性钙硫杆菌(At.caldus)菌株的硫氧化动力学进行了分批实验研究。Contois速率表达准确描述了硫酸钙生成(R2>0.93)和微生物生长(R2>0.87)。对于维持在45°C下的培养物,最大比生长速率(μmax)为0.105 h-1,生物质硫酸盐产量(Ypx)为4.8 x 10-9 mg SO42-.cell-1,Contois亲和系数(Kx)为1.56 x 10-8 mg S.cell-1。SCN-(0mg/L-20mg/L)在本体溶液中的存在竞争性地抑制了微生物系统。此外,SCN-不同程度地阻碍微生物生长;因此,速率表达相对于SCN-浓度进行分配,并确定每个区域的抑制常数(Ki)。适应离散浓度的SCN-(1mg/L和20mg/L)提高了At.caldus对SCN-的耐受性;然而,与未适应的对照菌株相比,适应菌株在无硫氰酸盐的条件下培养时表现出降低的硫氧化潜力。为了准确描述适应的系统,对Contois亲和系数(Kx)进行了修正,以反映疑似代谢下降。衍生的Kx值在幅度上增加,并证实了微生物底物亲和力或底物吸附能力的固有降低。将这些更新的Kx常数包含在速率方程中,适当地代表了R2>0.94的两种适应的At.caldus菌株的实验数据。此外,还综述了适应对SCN暴露的抑制动力学和抑制机制的影响。硫氰酸盐在适应菌株中非竞争性地抑制硫氧化,抑制机制的转变可能归因于适应后代谢状态的损害。