IL-17在黏附侵袭性大肠杆菌感染小鼠结肠过程中的作用机制研究

目的:评价IL-17在黏附侵袭性大肠杆菌感染小鼠结肠过程中的作用及其可能机制。方法:选择野生型及IL-17基因敲除的SPF级C57BL/6小鼠并随机分成4组,分别给予不同的处理:(1)野生小鼠+单纯蒸馏水灌胃处理组;(2)野生小鼠+E.coli LF82(1×109/CFU/只)灌胃10天处理组;(3)IL-17敲除小鼠+单纯蒸馏水灌胃处理组;(4)IL-17敲除小鼠+E.coli LF82灌胃10天处理组。从以下5个方面评价各组小鼠的炎症反应和IL-17水平:(1)组织病理评分评估炎症反应严重程度;(2)透射电镜下观察结肠上皮细胞的超微结构;(3)免疫组织化学检测结肠分泌的IL-17;(4)PCR检测小鼠结肠中IL-17m RNA表达;(5)ELISA检测结肠组织中IL-17的含量。结果:定植了E.coli LF82的IL-17敲除小鼠肠道炎症程度和超微结构损伤较野生型小鼠更加严重(P0.05)。与未经E.coli LF82处理组相比,定植了E.coli LF82的野生小鼠肠道中IL-17m RNA和IL-17含量明显升高(P0.05)。结论:IL-17在E.coli LF82在黏附侵袭结肠粘膜过程中的保护作用,IL-17是针对AIEC菌株E.coli LF82免疫的重要效应物,而结肠局部分泌增加的IL-17会改善感染的结果。     

大肠埃希菌蛋白指纹图谱的建立

目的建立大肠埃希菌（Escherichia coli,E．coli）蛋白指纹图谱,为Ecoli感染快速诊断奠定基础。方法收集临床分离E.coli88株,提取细菌DNA,PCR检测Ecoli 16S rRNA。蛋白提取液提取细菌蛋白,干化学法测蛋白浓度,应用表面增强激光解析电离飞行时间质谱技术（SELDI-TOF-MS）检测Ecoli蛋白,采用Ciphergen Pro-teinchip软件自动采集数据。重复测定20次Ecoli混合标本,评价SELDI检测Ecoli蛋白分子量的重复性。结果E．coil标准菌株ATCC 25922和临床分离株均可检出16S rRNA。AU芯片能捕获近30个E．coli蛋白峰,其中19个蛋白峰构成E．coli特征性蛋白指纹图谱,各蛋白峰在临床分离E．coli间分子量变异系数≤0．2％。SELDI重复检测20次E．coli混合标本显示同一蛋白峰的分子量变异系数≤0．05％。结论E．coli在分子量3～20kD范围内具有特征性蛋白指纹图谱,为快速诊断E.coli感染提供了新思路。     

基于双工程菌的“锁扣”生物活材料构建及其体内肠道滞留应用

生物活材料的研究主要集中在利用单一细菌生产生物膜、水塑料等体外应用。由于菌株尺寸较小，当其应用于体内时，容易发生逃逸，导致滞留效果较差。为解决这一难题，本研究借助大肠杆菌(Escherichia coli)表面展示系统(Neae)，在两个菌株表面分别展示SpyTag和SpyCatcher，构建一种双菌“锁扣”型生物活材料生产系统。两菌株之间通过SpyTag和SpyCatcher的结合，发生原位交联，从而长时间滞留在肠道部位。体外实验表明两菌株混合几分钟后，会发生明显的沉降。此外，利用共聚焦成像和微流控平台进一步证明了该系统在流动状态下的粘附效果。最后，为了验证该系统在体内应用的可行性，小鼠连续3d口服A菌(p15A-Neae-SpyTag/sfGFP)和B菌(p15A-Neae-SpyCatcher/mCherry)，收集肠道组织进行冷冻切片染色。结果表明，相较于未结合菌株，该双菌系统能更多滞留在小鼠肠道，为生物活材料进一步的体内应用奠定了基础。     

东亚飞蝗细胞色素P450基因的克隆及表达分析

本文克隆了东亚飞蝗Locusta migratoria manilensis(Meyen)细胞色素P450(cytochrome P450)基因全长,表达重组蛋白,并对其可溶性进行了分析。通过提取东亚飞蝗总的RNA,反转录成cDNA,设计特异性引物,PCR克隆东亚飞蝗细胞色素P450基因,将测序正确的目的片段克隆至原核表达载体pET-28a中,在大肠埃希菌Escherichia coli Rosetta中用异丙基-β-D-硫代半乳糖苷(IPTG)诱导表达。用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)检测重组蛋白表达结果。结果表明:东亚飞蝗细胞色素P450基因开放阅读框全长为1 551 bp,编码516个氨基酸,与GenBank中已登录的东亚飞蝗细胞色素P450基因(HM153426)的同源性为99%,重组质粒pET-28a-P450在E.coli Rosetta中获得高效表达,重组蛋白相对分子质量(Mr)约为53 000,主要以包涵体的形式存在。     

改良环介导等温扩增技术快速检测肉类中的大肠杆菌O157: H7

针对大肠杆菌O157:H7(Escherichia coli O157:H7,E.coli O157:H7)传统检测方法检测周期长的问题,建立了肉类中的E.coli O157:H7的改良环介导等温扩增(LAMP)快速检测方法。以E.coli O157:H7的O157特异性抗原rfbE基因、鞭毛H7特异性抗原fliC基因序列作为靶序列,分别设计2套增加了环引物的改良LAMP引物序列,单管同时检测,通过肉眼观察白色沉淀,判断检测结果。采用36株细菌验证了该改良LAMP引物的特异性。热裂解法提取的DNA经改良LAMP体系扩增20 min,检测E.coli O157:H7的灵敏度为1.4 CFU/mL,人工污染肉中的E.coli O157:H7检出限为1.8 CFU/g。137份实样中,检测出1份E.coli O157:H7假阳性,与行业标准SNT0973-2000符合率达到99.3%。     

结核分枝杆菌分泌蛋白Ag85B、Hsp16.3和ESAT6在血清学检测中 的初步应用

目的:探讨结核分枝杆菌分泌蛋白Hsp16.3、Ag85B以及融合蛋白ESAT6-CFP10、Ag85B-Hsp16.3和Ag85B-ESAT6用于TB病人血清学检测的意义。方法:将已构建的含5种目的基因的表达载体(pProEXHTb-Hsp16.3、pProEXHTa-Ag85B、pProEXHTb-ESAT6-CFP10、pProEXHTa-Ag85B-Hsp16.3、pProEXHTa-Ag85B-ESAT6),分别转入宿主菌E.coli DH5α中,诱导表达后分别获得Hsp16.3、Ag85B、ESAT6-CFP10、Ag85B-Hsp16.3和Ag85B-ESAT6五种蛋白,采用Ni2+亲和层析柱进行纯化,并用透析方法进行目的蛋白的复性。将经过复性的5种蛋白分别作为抗原,采用间接ELISA方法检测待测的血清样本,经OPD显色,测定各孔OD490值并判定结果。结果:五种蛋白被成功纯化并复性,通过ELISA方法共检测了22例TB病人血清、10例非结核病人血清和6例正常对照血清,Hsp16.3、Ag85B、ESAT6-CFP10、Ag85B-Hsp16.3和Ag85B-ESAT6这5种抗原的灵敏度分别为36.4%、90.9%、77.3%、95.5%、100%,特异性分别为100%、75%、100%、93.8%、93.8%。统计分析显示,ESAT6-CFP10和Ag85B、Ag85B-Hsp16.3、Ag85B-ESAT6这三种蛋白ELISA检测的结果无差异,而与Hsp16.3和痰涂片检测结果有显著差异。结论:Ag85B-Hsp16.3和Ag85B-ESAT6可作为结核分枝杆菌ELISA检测的初选抗原。     

结核分枝杆菌分泌蛋白Ag85B、Hsp16.3和ESAT6在血清学检测中的初步应用

目的：探讨结核分枝杆菌分泌蛋白Hsp16.3、Ag85B以及融合蛋白ESAT6-CFP10、Ag85B-Hsp16.3和Ag85B-ESAT6用于TB病人血清学检测的意义。方法：将已构建的含5种目的基因的表达载体（pProEXHTb-Hsp16.3、pProEXHTa-Ag85B、pProEXHTb-ESAT6-CFP10、pProEXHTa-Ag85B-Hsp16.3、pProEXHTa-Ag85B-ESAT6）,分别转入宿主菌E.coli DH5α中,诱导表达后分别获得Hsp16.3、Ag85B、ESAT6-CFP10、Ag85B-Hsp16.3和Ag85B-ESAT6五种蛋白,采用Ni2＋亲和层析柱进行纯化,并用透析方法进行目的蛋白的复性。将经过复性的5种蛋白分别作为抗原,采用间接ELISA方法检测待测的血清样本,经OPD显色,测定各孔OD490值并判定结果。结果：五种蛋白被成功纯化并复性,通过ELISA方法共检测了22例TB病人血清、10例非结核病人血清和6例正常对照血清,Hsp16.3、Ag85B、ESAT6-CFP10、Ag85B-Hsp16.3和Ag85B-ESAT6这5种抗原的灵敏度分别为36.4%、90.9%、77.3%、95.5%、100%,特异性分别为100%、75%、100%、93.8%、93.8%。统计分析显示,ESAT6-CFP10和Ag85B、Ag85B-Hsp16.3、Ag85B-ESAT6这三种蛋白ELISA检测的结果无差异,而与Hsp16.3和痰涂片检测结果有显著差异。结论：Ag85B-Hsp16.3和Ag85B-ESAT6可作为结核分枝杆菌ELISA检测的初选抗原。     

通过染色体整合表达古菌乙酰化酶合成N-末端乙酰化胸腺肽β4

胸腺肽β4（Tβ4）是N-末端乙酰化的43肽,具有多种重要生物学功能.其生物合成存在两大难点,即乙酰化修饰和小分子肽的表达.本研究发现来自古菌Sulfolobus solfataricus的乙酰化酶ssArd1可以催化Tβ4的N-末端乙酰化修饰.利用Red同源重组技术将ssArd1基因表达盒整合至E.coli BL21（DE3）染色体的lpxM位点上,构建了可以实现Tβ4N-末端乙酰化修饰的新型宿主E.coli BDA.将Tβ4编码基因融合在改造的微型Spl DnaX Intein的N端,并在Intein的C端添加His标签,构建了表达载体pET-Tβ4-Intein.在E.coli BDA中表达的融合蛋白,经镍亲和层析纯化后用β-巯基乙醇诱导融合蛋白切割释放小分子多肽,获得了具有N-末端乙酰化的Tβ4.     

用于Escherichia coli O157∶H7直接快速检测的倏逝波荧光核酸适配体传感器研究

通过融合倏逝波荧光光纤传感器和特异性核酸适配体的优势,提出了一种基于倏逝波荧光原理及其与病原菌尺寸效应的Escherichia coli O157∶H7(E.coli O157∶H7)直接快速检测方法。基本原理是当一定浓度荧光标记E.coli O157∶H7核酸适配体加入样品检测池时,倏逝波激发荧光分子发出荧光,利用倏逝波全光纤生物传感器即可实现荧光信号的定量检测;当荧光标记的核酸适配体与E.coli O157∶H7混合后加入样品检测池,因倏逝波渗入深度仅为100 nm,导致特异性结合E.coli O157∶H7的核酸适配体标记荧光分子不能被激发,从而使得检测荧光信号降低;利用荧光信号强度与E.coli O157∶H7浓度的比例关系即可实现其定量检测。结果表明:该方法检测E.coli O157∶H7的检测限可达610 CFU/mL,线性检测区间为1.1×10~3-1.4×10~7 CFU/mL。实际水样加标回收率在40%-180%之间,相对标准偏差在10%之内,水样基质对E.coli O157∶H7的检测没有明显影响。本研究建立基于倏逝波荧光原理及其与病原菌尺寸效应的生物传感分析方法具有普适性,仅需使用不同荧光标记的生物识别分子即可实现其他病原菌的直接快速检测。     

嗜酸乳杆菌S-层蛋白联合抗生素对Escherichia coli和Staphylococcus aureus的抑制作用研究

旨在检测嗜酸乳杆菌S-层蛋白以及S-层蛋白与抗生素联用对大肠杆菌(Escherichia coli)和金黄色葡萄球菌(Staphylococcus aureus)的抑制作用。采用液体发酵培养法获得嗜酸乳杆菌菌体,LiCl法提取S-层蛋白粗提物,凝胶过滤层析法纯化S-层蛋白,分别用E.coli和S.aureus处理Caco-2细胞2 h后,考察S-层蛋白在不同浓度和不同作用时间条件下对E.coli和S.aureus的抑制作用,并考察S-层蛋白联合抗生素对E.coli和S.aureus的抑制作用,实验分组:(1)空白对照;(2)嗜酸乳杆菌组;(3)S-层蛋白组;(4)抗生素组;(5)嗜酸乳杆菌+抗生素组;(6)S-层蛋白+抗生素组。结果显示,液体发酵得到嗜酸乳杆菌菌体,提取并纯化得到S-层蛋白;S-层蛋白对E.coli和S.aureus有很好的抑制效果,具有浓度依赖性,高浓度下抑制率达到42.2%和31.7%,差异极显著(P<0.01),且在E.coli和S.aureus作用的短时间内干预效果明显,0 h时的抑制率分别达到59.3%和48.4%;S-层蛋白联合抗生素的抑菌率分别达到81.7%和79.3%,差异极显著(P<0.01),效果优于单独使用抗生素。嗜酸乳杆菌S-层蛋白具有较强的抑菌作用,可以与抗生素联用,有望开发称为一种新型的抗菌药物。     

Determination of tetrathionate and thiosulfate in natural samples and microbial cultures by a new, fast and sensitive ion chromatographic technique

Abstract A new isocratic ion chromatographic technique is described for the sensitive measurement of tetrathionate, trithionate and thiosulfate. The sulfur oxyanions were separated on a polymer-coated, silica-based anion exchange column and directly detected by UV absorption at 216 nm. Aqueous saline acetonitrile/methanol mixtures were used as eluent. The three anions could be quantified in less than 10 min with detection limits of about 0.6 pmol for tetrathionate and of 40 and 10 pmol for trithionate and thiosulfate, respectively. The retention times of tetrathionate responded to changes of the solvent concentration, whereas the elution of thiosulfate depended predominatly on the ionic strenght of the eluent. Starting at the lowest detectable concentrations, calibration curves for all three compounds were linear over a concentration range of three orders of magnitude. The analysis of freshwater and saline samples worked equally well. Since contact of the eluent with metallic components caused shifts in retention times during operation, the solvent delivery system had to consist of plastic material. Examples of applicaton are given for determination of tetrathionate and thiosulfate in natural samples and for the turnover of these two compounds in sediment slurries and anaerobic enrichment cultures.     

Reduction of inorganic sulphur compounds by facultatively aerobic bacteria

Summary Amongst the family of the Enterobacteriaceae the ability to reduce tetrathionate to thiosulfate and thiosulfate to sulfite and sulfide occurs in the genera Proteus, Citrobacter and Salmonella. These reductions are coupled to a respiratory chain which functions under anaerobic conditions. Only during transport of electrons to tetrathionate oxidative phosphorylation has been demonstrated. Isolation and purification of the cytoplasmic membrane bound tetrathionate and thiosulfate reductase fromProteus mirabilis makes clear that this bacterium forms only one enzyme for both reductions. This enzyme has a molecular weight of 133,000 daltons and can be divided into two subunits with molecular weights of 43,000 and 90,000 daltons by treatment with sodium dodecyl sulfate and 2-mercaptoethanol. The reduction of tetrathionate is activated by its primary product thiosulfate. Nitrate or oxygen represses and inactivates the tetrathionate and thiosulfate reductase. Nevertheless the smaller subunit of this enzyme appears to be formed and assembled into the cytoplasmic membranes after anaerobic growth in the presence of nitrate. Paper read at the Symposium on the Sulphur Cycle, Wageningen, May 1974.     

Thiosulfate oxidation by obligately heterotrophic bacteria

Thiosulfate was oxidized stoichiometrically to tetrathionate during growth on glucose byKlebsiella aerogenes, Bacillus globigii, B. megaterium, Pseudomonas putida, two strains each ofP. fluorescens andP. aeruginosa, and anAeromonas sp. A gram-negative, rod-shaped soil isolate, Pseudomonad H_w, converted thiosulfate to tetrathionate during growth on acetate. None of the organisms could use thiosulfate as sole energy source. The quantitative recovery of all the thiosulfate supplied to heterotrophic cultures either as tetrathionate alone or as tetrathionate and unused thiosulfate demonstrated that no oxidation to sulfate occurred with any of the strains tested. Two strains ofEscherichia coli did not oxidize thiosulfate. Thiosulfate oxidation in batch culture occurred at different stages of the growth cycle for different organisms:P. putida oxidized thiosulfate during lag and early exponential phase,K. aerogenes oxidized thiosulfate at all stages of growth, andB. megaterium andAeromonas oxidized thiosulfate during late exponential phase. The relative rates of oxidation byP. putida andK. aerogenes were apparently determined by different concentrations of thiosulfate oxidizing enzyme. Thiosulfate oxidation byP. aeruginosa grown in chemostat culture was inducible, since organisms pregrown on thiosulfate-containing media oxidized thiosulfate, but those pregrown on glucose only could not oxidize thiosulfate. Steady state growth yield ofP. aeruginosa in glucose-limited chemostat culture increased about 23% in the presence of 5–22 mM thiosulfate, with complete or partial concomitant oxidation to tetrathionate. The reasons for this stimulation are unclear. The results suggest that heterotrophic oxidation of thiosulfate to tetrathionate is widespread across several genera and may even stimulate bacterial growth in some organisms.     

Inhibitory Action of Tetrathionate Enrichment Broth

Tetrathionate enrichment broth is a complex mixture of salts including iodides and other polythionates, but only thiosulfate (0.0736 m) and tetrathionate (0.0236 m) in combination were toxic for Escherichia coli. Individually, these two salts were not lethal. The lethal action of this thiosulfate-tetrathionate mixture affected only growing cells. A possible relationship between the lethality of the thiosulfate-tetrathionate mixture for a culture and its ability to reduce tetrathionate is suggested.     

Engineering bacterial thiosulfate and tetrathionate sensors for detecting gut inflammation

There is a groundswell of interest in using genetically engineered sensor bacteria to study gut microbiota pathways, and diagnose or treat associated diseases. Here, we computationally identify the first biological thiosulfate sensor and an improved tetrathionate sensor, both two‐component systems from marine Shewanella species, and validate them in laboratory Escherichia coli. Then, we port these sensors into a gut‐adapted probiotic E. coli strain, and develop a method based upon oral gavage and flow cytometry of colon and fecal samples to demonstrate that colon inflammation (colitis) activates the thiosulfate sensor in mice harboring native gut microbiota. Our thiosulfate sensor may have applications in bacterial diagnostics or therapeutics. Finally, our approach can be replicated for a wide range of bacterial sensors and should thus enable a new class of minimally invasive studies of gut microbiota pathways.     

Constructed molecular sensor to enhance metal detection by bacterial ribosomal switch-ion channel protein interaction

Molecular biosensors are useful tools that detect metal ions or other potentially toxic chemicals. However, the efficiency of conventional sensors is limited in mixed metals substrates, which is the common way they are found in nature. The use of biosensors constructed from genetically modified living microbial systems has the potential of providing sensitive detection systems for specific toxic targets. Consequently, our investigation was aimed at assembling different genetic building blocks to produce a focused microbial biosensor with the ability to detect specific metals. This objective was achieved by using a synthetic biology approach. Our genetic building blocks, including a synchronized ribosomal switch-iron ion channel, along with sequences of promoters, metal-binding proteins (Fe, Pb), ribosomal binding sites, yellow fluorescence reporter protein (YFRP), and terminators, were constructed within the same biobrick in Escherichia coli. We used an rpoS ribosomal switch containing an aptamer, which responds to the specific metal ligands, in synchronization with an iron ion channel, TonB. This switch significantly stimulates translation, as expressed by higher fluorescence, number of colonies, and concentration of RNA in E. coli. The positive results show the effectiveness of using genetically tailored synchronized ribosomal switch-ion channels to construct microbial biosensors to detect specific metals, as tested in iron solutions.     

Reduced sulfur compound oxidation by Thiobacillus caldus.

The oxidation of reduced inorganic sulfur compounds was studied by using resting cells of the moderate thermophile Thiobacillus caldus strain KU. The oxygen consumption rate and total oxygen consumed were determined for the reduced sulfur compounds thiosulfate, tetrathionate, sulfur, sulfide, and sulfite in the absence and in the presence of inhibitors and uncouplers. The uncouplers 2,4-dinitrophenol and carbonyl cyanide m-chlorophenyl-hydrazone had no affect on the oxidation of thiosulfate, suggesting that thiosulfate is metabolized periplasmically. In contrast, the uncouplers completely inhibited the oxidation of tetrathionate, sulfide, sulfur, and sulfite, indicating that these compounds are metabolized in the cytoplasm of T. caldus KU. N-Ethylmaleimide inhibited the oxidation of tetrathionate and thiosulfate at the stage of elemental sulfur, while 2-heptyl-4-hydroxyquinoline-N-oxide stopped the oxidation of thiosulfate, tetrathionate, and elemental sulfur at the stage of sulfite. The following intermediates in the oxidation of the sulfur compounds were found by using uncouplers and inhibitors: thiosulfate was oxidized to tetrathionate, elemental sulfur was formed during the oxidation of tetrathionate and sulfide, and sulfite was found as an intermediate of tetrathionate and sulfur metabolism. On the basis of these data we propose a model for the metabolism of the reduced inorganic sulfur compounds by T. caldus KU.     

Homologs from sulfur oxidation (Sox) and methanol dehydrogenation (Xox) enzyme systems collaborate to give rise to a novel pathway of chemolithotrophic tetrathionate oxidation

The SoxXAYZB(CD)₂‐mediated pathway of bacterial sulfur‐chemolithotrophy explains the oxidation of thiosulfate, sulfide, sulfur and sulfite but not tetrathionate. Advenella kashmirensis, which oxidizes tetrathionate to sulfate, besides forming it as an intermediate during thiosulfate oxidation, possesses a soxCDYZAXOB operon. Knock‐out mutations proved that only SoxBCD is involved in A. kashmirensis tetrathionate oxidation, whereas thiosulfate‐to‐tetrathionate conversion is Sox independent. Expression of two glutathione metabolism‐related proteins increased under chemolithotrophic conditions, as compared to the chemoorganotrophic one. Substrate‐dependent oxygen consumption pattern of whole cells, and sulfur‐oxidizing enzyme activities of cell‐free extracts, measured in the presence/absence of thiol inhibitors/glutathione, corroborated glutathione involvement in tetrathionate oxidation. Furthermore, proteome analyses detected a sulfite:acceptor oxidoreductase (SorAB) exclusively under chemolithotrophic conditions, while expression of a methanol dehydrogenase (XoxF) homolog, subsequently named thiol dehydrotransferase (ThdT), was found to increase 3‐ and 10‐fold during thiosulfate‐to‐tetrathionate conversion and tetrathionate oxidation respectively. A thdT knock‐out mutant did not oxidize tetrathionate but converted half of the supplied 40 mM S‐thiosulfate to tetrathionate. Knock‐out of another thiosulfate dehydrogenase (tsdA) gene proved that both ThdT and TsdA individually converted ～ 20 mM S‐thiosulfate to tetrathionate. The overexpressed and isolated ThdT protein exhibited PQQ‐dependent thiosulfate dehydrogenation, whereas its PQQ‐independent thiol transfer activity involving tetrathionate and glutathione potentially produced a glutathione:sulfodisulfane adduct and sulfite. SoxBCD and SorAB were hypothesized to oxidize the aforesaid adduct and sulfite respectively.     

Activation of bovine plasminogen by Streptococcus uberis

Abstract Thiosulfate and tetrathionate oxidation activity of Thiobacillus ferrooxidans were found to be absent in iron-growth cell as well as in the cells grown anaerobically on elemental sulfur. While the thiosulfate oxidase activity was absent in the cell-free extract of the above cells, the activity of rhodanese was present irrespective of the culture condition of T. ferrooxidans . It is thus conceivable that rhodanese is not involved in thiosulfate metabolism. During growth in presence of ferrous sulfate plus elemental sulfur, the thiosulfate/tetrathionate oxidation activity was absent till the oxidation of ferrous iron was complete and the cells harvested only in the latter period acquired the thiosulfate/tetrathionate oxidation activity. Thus it becomes evident that the inhibition of thiosulfate and tetrathionate oxidation is solely due to presence of ferrous iron.     

Studies on Biochemistry of the Thiobacilli

In the oxidation of thiosulfate at pH 4.5 tetrathionate was formed as an intermediate, and the thiosulfate-oxidizing enzyme was active in acidic pH range in contrast to the enzyme of T. thioparus and Thiobacillus X.

Phosphate did not seem to affect the oxidation of thiosulfate but rather affect the conversion of tetrathionate. In the absence of phosphate, tetrathionate, which was produced from thiosulfate oxidation, seemed to accumulate without undergoing further conversion.

Quantitative oxidation of tetrathionate to sulfate was achieved with freshly harvested cells of T. thiooxidans; pH optimum for the oxidation of tetrathionate by the washed cells was 2~3, and the activity fell markedly at pH above 3.5.

Tetrathionate might be enzymatically dismuted to pentathionate and trithionate under anaerobic conditions with crude extracts of T. thiooxidans; pH optimum for the reaction was about 2.7 and the activity fell strikingly at pH 4.7. The formed trithionate might be further hydrolyzed to thiosulfate and sulfate.