Enhancement of bio-promoters on hexavalent chromium inhibited sulfur-driven denitrification: repairing damage, accelerating electron transfer, and reshaping microbial collaboration.

Proposing recovery strategies to recover heavy-metal-inhibited sulfur-driven denitrification, as well as disclosing recovery mechanisms, can provide technical support for the stable operation of bio-systems. This study proposed an effective bio-promoter (mediator-promoter composed of L-cysteine, biotin, cytokinin, and anthraquinone-2,6-disulfonate) to recover Cr(VI) inhibited sulfur-driven denitrification, which effectively reduced the recovery time of NO3--N reduction (18-21 cycles) and NO2--N reduction (27-42 cycles) compared with self-recovery. The mediator-promoter repaired microbial damage by promoting intracellular chromium efflux. Moreover, the mediator-promoter reduced the accumulated reactive oxygen species by stimulating the secretion of antioxidant enzymes, reaching equilibrium in the oxidative-antioxidant system. To improve electron transmission, the mediator-promoter restored S2O32- oxidation to provide adequate electron donors and increased electron transfer rate by increasing cytochrome c levels. Mediator-promoter boosted the abundance of Thiobacillus (sulfur-oxidizing bacterium) and Simplicispira (denitrifying bacterium), which were positively correlated, facilitating the rapid denitrification recovery and the long-term stable operation of recovered systems.

Sulfur enhances cadmium bioaccumulation in Cichorium intybus by altering soil properties, heavy metal availability and microbial community in contaminated alkaline soil.

Cadmium (Cd) contamination seriously threatens the soil health and food safety. Combination of amendment and accumulator plant is a green and effective technique to improve phytoremediation of Cd-contaminated alkaline soil. In this study, a potting experiment was conducted to investigate the effect of sulfur on Cd phytoextraction by Cichorium intybus (chicory). Soil chemical and microbial properties were determined to reveal the mechanism of sulfur-assisting Cd phytoremediation by chicory. Soil pH decreased from 7.77 to the lowest 7.30 with sulfur addition (0.6, 0.9 and 1.2 g kg-1, LS, MS and HS treatment); Electric conductivity, sulfate anion and available cadmium concentration increased gradually with increasing sulfur doses. Cd concentration of shoot and root significantly increased from 1.47 to 4.43 mg kg-1, 6.15 to 20.16 mg kg-1 by sulfur treatment relative to CK, which were attributed to increased available Cd concentration induced by decreased pH. Sulfur treatments significantly increased the Cd bioconcentration factor by 64.1%, 118.6%, 201.0% for shoot, 76.3%, 145.6% and 227.7% for root under LS, MS and HS relative to CK treatment, respectively (P < 0.05). However, only MS treatment significantly improved the Cd removal efficiency by 82.9% in comparison of CK treatment (P < 0.05). Microbial community diversity measured by 16SrRNA showed that Thiobacillus and Actinobacteria were the key and dominant strains of soil microbial communities after sulfur addition, which played a pivotal role in the process of sulfur oxidation involved in decrease of soil pH and the transformation of Cd forms. Correlation analysis and path analysis by structural equation model indicated that soil sulfate anion and Thiobacillus directly affected Cd removal efficiency by chicory in Cd-contaminated alkaline soil. This suggests that combination of sulfur and chicory may provide a way to promote Cd bioaccumulation for phytoremediation of Cd-contaminated alkaline soil.

DL-cysteine and L-cystine formation and their enhancement effects during sulfur autotrophic denitrification.

Sulfur autotrophic denitrification has been proved feasible for nitrate removal from aquatic environments and it utilizes elemental sulfur as the electron donor. A maximum denitrification rate of 194.57 mg N/L·d was achieved with biogenic sulfur as electron donor in a mixed culture collected from sulfur packed bed reactors; this rate was considerably higher than that delivered by α-S8 or µ-S in the same mixed culture. The elemental sulfur was also tested in the pure culture of Thiobacillus denitrificans, while a lower denitrification rate was noted than in the mixed culture, bio-S (4.86 mg N/L·d) again outperformed other two elemental sulfur's. X-ray absorption near edge structure spectra were collected to examine possible metabolic intermediates during the sulfur autotrophic denitrification process. The analysis revealed the existence of two major intermediates: DL-cysteine and L-cystine. They were found to not only provide electrons but also play a critical role in promoting the elemental sulfur-mediated sulfur autotrophic denitrification process. In general, we investigated the formation and enhancement effects of sulfur intermediates in the sulfur autotrophic denitrification process.

Effects of sulfur application on cadmium bioaccumulation in tobacco and its possible mechanisms of rhizospheric microorganisms.

A potting experiment was conducted to investigate the effect of sulfur application on the bioaccumulation by tobacco and its mechanisms of rhizospheric microorganisms. Cadmium content in tobacco was analyzed using atomic absorption spectrometer, while bacterial community and related gene in soil were analyzed via high-throughput sequencing and quantitative PCR techniques, respectively. The obtained results indicated that tobacco had the ability to accumulate cadmium under no sulfur application conditions, with cadmium contents of 35.4, 23.6, and 26.3 mg kg-1 in leaves, stems, and roots, respectively. Under high-sulfur treatment, these values increased to 66.4, 46.1, and 42.6 mg kg-1, respectively, probably due to the increase of the available cadmium content (from 1.1 to 3.3 mg kg-1) in the soil through a decrease of the soil pH value, which was contributed by the sulfur oxidation reaction. dsrA and soxB genes might play an important role in sulfur oxidation, and Thiobacillus sp. was the dominant bacterial genus during the sulfur oxidation process. In addition, sulfur application exerted little effect on the diversity and structure of the soil bacterial community. The combined results indicate that sulfur application is an effective and safe method for Cd phytoextraction by tobacco.

Cysteine-mediated decyanation of vitamin B12 by the predicted membrane transporter BtuM.

Uptake of vitamin B12 is essential for many prokaryotes, but in most cases the membrane proteins involved are yet to be identified. We present the biochemical characterization and high-resolution crystal structure of BtuM, a predicted bacterial vitamin B12 uptake system. BtuM binds vitamin B12 in its base-off conformation, with a cysteine residue as axial ligand of the corrin cobalt ion. Spectroscopic analysis indicates that the unusual thiolate coordination allows for decyanation of vitamin B12. Chemical modification of the substrate is a property other characterized vitamin B12-transport proteins do not exhibit.

Improved quinoa growth, physiological response, and seed nutritional quality in three soils having different stresses by the application of acidified biochar and compost.

Quinoa (Chenopodium quinoa Willd.) is a traditional Andean agronomical resilient seed crop having immense significance in terms of high nutritional qualities and its tolerance against various abiotic stresses. However, finite work has been executed to evaluate the growth, physiological, chemical, biochemical, antioxidant properties, and mineral nutrients bioavailability of quinoa under abiotic stresses. Depending on the consistency in the stability of pH, intended rate of S was selected from four rates (0.1, 0.2, 0.3, 0.4 and 0.5% S) for the acidification of biochar and compost in the presence of Thiobacillus thiooxidans by pH value of 4. All three soils were amended with 1% (w/w) acidified biochar (BCA) and compost (COA). Results revealed that selective plant growth, yield, physiological, chemical and biochemical improved significantly by the application of BCA in all stressed soils. Antioxidants in quinoa fresh leaves increased in the order of control > COA > BCA, while reactive oxygen species decreased in the order of control < COA < BCA. A significant reduction in anti-nutrients (phytate and polyphenols) was observed in all stressed soils with the application of BCA. Moreover, incorporation of COA and BCA reduced the pH of rhizosphere soil by 0.4-1.6 units in all stressed soils, while only BCA in bulk soil decreased pH significantly by 0.3 units. These results demonstrate that BCA was more effective than COA to enhance the bioavailability, translocation of essential nutrients from the soil to plant and their enhanced bioavailability in the seed.

A Novel Uncultured Bacterium of the Family Gallionellaceae: Description and Genome Reconstruction Based on the Metagenomic Analysis of Microbial Community in Acid Mine Drainage.

Drainage waters at the metal mining areas often have low pH and high content of dissolved metals due to oxidation of sulfide minerals. Extreme conditions limit microbial diversity in- such ecosystems. A drainage water microbial community (6.5'C, pH 2.65) in an open pit at the Sherlovaya Gora polymetallic open-cast mine (Transbaikal region, Eastern Siberia, Russia) was studied using metagenomic techniques. Metagenome sequencing provided information for taxonomic and functional characterization of the micro- bial community. The majority of microorganisms belonged to a single uncultured lineage representing a new Betaproteobacteria species of the genus Gallionella. While no.acidophiles are known among the cultured members of the family Gallionellaceae, similar 16S rRNA gene sequences were detected in acid mine drain- ages. Bacteria ofthe genera Thiobacillus, Acidobacterium, Acidisphaera, and Acidithiobacillus,-which are com- mon in acid mine drainage environments, were the minor components of the community. Metagenomic data were -used to determine the almost complete (-3.4 Mb) composite genome of the new bacterial. lineage desig- nated Candidatus Gallionella acididurans ShG14-8. Genome analysis revealed that Fe(II) oxidation probably involved the cytochromes localized on the outer membrane of the cell. The electron transport chain included NADH dehydrogenase, a cytochrome bc1 complex, an alternative complex III, and cytochrome oxidases of the bd, cbb3, and bo3 types. Oxidation of reduced sulfur compounds probably involved the Sox system, sul- fide-quinone oxidoreductase, adenyl sulfate reductase, and sulfate adenyltransferase. The genes required for autotrophic carbon assimilation via the Calvin cycle were present, while no pathway for nitrogen fixation was revealed. High numbers of RND metal transporters and P type ATPases were probably responsible for resis- tance to heavy metals. The new microorganism was an aerobic chemolithoautotroph of the group of psychrotolerant iron- and sulfur-oxidizing acidophiles of the family Gallionellaceae, which are common in acid mine drainages.

System evaluation and microbial analysis of a sulfur cycle-based wastewater treatment process for Co-treatment of simple wet flue gas desulfurization wastes with freshwater sewage.

A sulfur cycle-based wastewater treatment process, namely the Sulfate reduction, Autotrophic denitrification and Nitrification Integrated process (SANI(®) process) has been recently developed for organics and nitrogen removal with 90% sludge minimization and 35% energy reduction in the biological treatment of saline sewage from seawater toilet flushing practice in Hong Kong. In this study, sulfate- and sulfite-rich wastes from simple wet flue gas desulfurization (WFGD) were considered as a potential low-cost sulfur source to achieve beneficial co-treatment with non-saline (freshwater) sewage in continental areas, through a Mixed Denitrification (MD)-SANI process trialed with synthetic mixture of simple WFGD wastes and freshwater sewage. The system showed 80% COD removal efficiency (specific COD removal rate of 0.26 kg COD/kg VSS/d) at an optimal pH of 7.5 and complete denitrification through MD (specific nitrogen removal rate of 0.33 kg N/kg VSS/d). Among the electron donors in MD, organics and thiosulfate could induce a much higher denitrifying activity than sulfide in terms of both NO3(-) reduction and NO2(-) reduction, suggesting a much higher nitrogen removal rate in organics-, thiosulfate- and sulfide-based MD in MD-SANI compared to sulfide alone-based autotrophic denitrification in conventional SANI(®). Diverse sulfate/sulfite-reducing bacteria (SRB) genera dominated in the bacterial community of sulfate/sulfite-reducing up-flow sludge bed (SRUSB) sludge without methane producing bacteria detected. Desulfomicrobium-like species possibly for sulfite reduction and Desulfobulbus-like species possibly for sulfate reduction are the two dominant groups with respective abundance of 24.03 and 14.91% in the SRB genera. Diverse denitrifying genera were identified in the bacterial community of anoxic up-flow sludge bed (AnUSB) sludge and the Thauera- and Thiobacillus-like species were the major taxa. These results well explained the successful operation of the lab-scale MD-SANI process.

Role of humic substances in promoting autotrophic growth in nitrate-dependent iron-oxidizing bacteria.

Nitrate-dependent iron oxidation was discovered in 1996 and has been reported from various environments ever since. To date, despite the widespread nature of this process, all attempts to cultivate chemolithoautotrophic nitrate-dependent iron oxidizers have been unsuccessful. The present study was focused on understanding the influence of natural chelating agents of iron, like humic substances, on the culturability, activity, and enumeration, of these microorganisms. Pure culture studies conducted with Thiobacillus denitrificans showed a constant increase in cell mass with a corresponding nitrate-dependent iron oxidation activity only when Fe(II) was provided together with humic substances, compared to no growth in control incubations without humic substances. The presence of a relatively strong chelating agent, such as EDTA, inhibited the growth of Thiobacillus denitrificans. It was concluded that complex formation between humic substances and iron was required for chemolithoautotrophic nitrate-dependent iron oxidation. Most probable number enumerations showed that numbers of chemolithoautotrophic nitrate-dependent iron-oxidizing bacteria were one to three orders of magnitude higher in the presence of humic substances compared to media without. Similar results were obtained when potential nitrate-dependent iron oxidation activity was determined in soil samples. In summary, this study showed that humic substances significantly enhanced the growth and activity of autotrophic nitrate-dependent iron-oxidizing microorganisms, probably by chelation of iron.

Mixed sulfur-iron particles packed reactor for simultaneous advanced removal of nitrogen and phosphorus from secondary effluent.

A mixed sulfur-iron particles packed reactor (SFe reactor) was developed to simultaneously remove total nitrogen (TN) and total phosphorus (TP) of the secondary effluent from municipal wastewater treatment plants. Low effluent TN (<1.5 mg/L) and TP (<0.3 mg/L) concentrations were simultaneously obtained, and high TN removal rate [1.03 g N/(L·d)] and TP removal rate [0.29 g P/(L·d)] were achieved at the hydraulic retention time (HRT) of 0.13 h. Kinetic models describing denitrification were experimentally obtained, which predicted a higher denitrification rate [1.98 g N/(L·d)] of SFe reactor than that [1.58 g N/(L·d)] of sulfur alone packed reactor due to the mutual enhancement between sulfur-based autotrophic denitrification and iron-based chemical denitrification. A high TP removal obtained in SFe reactor was attributed to chemical precipitation of iron particles. Microbial community analysis based on 16S rRNA revealed that autotrophic denitrifying bacteria Thiobacillus and Sulfuricella were the dominant genus, indicating that autotrophic denitrification played important role in nitrate removal. These results indicate that sulfur and iron particles can be packed together in a single reactor to effectively remove nitrate and phosphorus.

Toxins vapC and pasB from prokaryotic TA modules remain active in mammalian cancer cells.

Among the great number of addictive modules which have been discovered, only a few have been characterized. However, research concerning the adoption of toxins from these systems shows their great potential as a tool for molecular biology and medicine. In our study, we tested two different toxins derived from class II addictive modules, pasAB from plasmid pTF-FC2 (Thiobacillus ferrooxidans) and vapBC 2829Rv (Mycobacterium tuberculosis), in terms of their usefulness as growth inhibitors of human cancer cell lines, namely KYSE 30, MCF-7 and HCT 116. Transfection of the pasB and vapC genes into the cells was conducted with the use of two different expression systems. Cellular effects, such as apoptosis, necrosis and changes in the cell cycle, were tested by applying flow cytometry with immunofluorescence staining. Our findings demonstrated that toxins VapC and PasB demonstrate proapoptotic activity in the human cancer cells, regardless of the expression system used. As for the toxin PasB, observed changes were more subtle than for the VapC. The level of expression for both the genes was monitored by QPCR and did not reveal statistically significant differences within the same cell line.

Efficient CO2-reducing activity of NAD-dependent formate dehydrogenase from Thiobacillus sp. KNK65MA for formate production from CO2 gas.

NAD-dependent formate dehydrogenase (FDH) from Candida boidinii (CbFDH) has been widely used in various CO2-reduction systems but its practical applications are often impeded due to low CO2-reducing activity. In this study, we demonstrated superior CO2-reducing properties of FDH from Thiobacillus sp. KNK65MA (TsFDH) for production of formate from CO2 gas. To discover more efficient CO2-reducing FDHs than a reference enzyme, i.e. CbFDH, five FDHs were selected with biochemical properties and then, their CO2-reducing activities were evaluated. All FDHs including CbFDH showed better CO2-reducing activities at acidic pHs than at neutral pHs and four FDHs were more active than CbFDH in the CO2 reduction reaction. In particular, the FDH from Thiobacillus sp. KNK65MA (TsFDH) exhibited the highest CO2-reducing activity and had a dramatic preference for the reduction reaction, i.e., a 84.2-fold higher ratio of CO2 reduction to formate oxidation in catalytic efficiency (kcat/KB) compared to CbFDH. Formate was produced from CO2 gas using TsFDH and CbFDH, and TsFDH showed a 5.8-fold higher formate production rate than CbFDH. A sequence and structural comparison showed that FDHs with relatively high CO2-reducing activities had elongated N- and C-terminal loops. The experimental results demonstrate that TsFDH can be an alternative to CbFDH as a biocatalyst in CO2 reduction systems.

Biological removal of methanethiol from gas and water streams by using Thiobacillus thioparus: investigation of biodegradability and optimization of sulphur production.

The present work mainly deals with biological oxidation, which was tested using the bacterium Thiobacillus thioparus in semi-batch bioreactor systems to evaluate the removal efficiencies and optimal conditions for the biodegradation of methanethiol (MT) in order to treat the natural gas and refinery output streams. The efficiency of this method is analysed by evaluating the concentration of MT in a bioreactor. The effect of operational parameters, such as initial concentration of MT, pH, temperature, dissolved oxygen (DO), initial concentration of bacteria and reaction time on the degradation of MT, were studied. In this process, MT is converted into elemental sulphur particles as an intermediate in the oxidation process of MT to sulphate. The obtained results showed that the highest degradation rate occurred during the first 300 minutes of reaction time. The optimal conditions of the different initial MT concentrations with 0.3-0.6 bacteria OD, DO of 0.5 ppm, acidic pH value of 6.2 and temperature of 300C are obtained. Acidic pH and oxygen-limiting conditions were applied to obtain 80-85% selectivity for elemental sulphur formation in products. Under the optimal conditions, and for the highest (8.51 mM) and the lowest (0.53 mM) concentration of MT, the biological removal was about 89% and 94%, respectively.

Two arginine residues in the substrate pocket predominantly control the substrate selectivity of thiocyanate hydrolase.

Thiocyanate hydrolase (SCNase) of Thiobacillus thioparus THI115 is a cobalt (Co)-containing enzyme that catalyzes the hydrolysis of thiocyanate (SCN⁻), a major component of wastewater from coke oven factories, to carbonyl sulfide and ammonia. Although SCNase exhibits high structural similarities to Co-type nitrile hydratase (NHase), including a unique Co³âº catalytic center with two oxidized Cys ligands, both SCNase and NHase exclusively catalyze only their own substrates. Based on the differences in the substrate-binding pockets of these enzymes, ßArg90 and γArg136 of SCNase, with side chains extending toward the pocket, were separately substituted with Phe and Trp, the corresponding residues, respectively, in Co-type NHase. Both SCNase ßArg90 and SCNase γArg136 mutants showed no SCN⁻ hydrolysis activity but did catalyze the hydration of nitriles. The estimated kcat values (∼2 s⁻¹) corresponded to approximately 0.2% of that of Co-type NHase for nitrile hydration and approximately 3% of that of wild-type SCNase for SCN⁻ hydrolysis. The crystal structure of SCNase γR136W is essentially identical to that of the wild-type, including the Co³âº center having Cys oxidations; the size of the substrate pocket was enlarged because of conformational changes on the side chains of the mutated residue. Discussion of the difference in the environments around the substrate-binding pockets among the wild-type and mutant SCNases and Co-type NHase strongly suggests that ßArg90 and γArg136, positioned at the top of the Co³âº center, predominantly control the substrate selectivity of SCNase.

Pathways of sulfide oxidation by haloalkaliphilic bacteria in limited-oxygen gas lift bioreactors.

Physicochemical processes, such as the Lo-cat and Amine-Claus process, are commonly used to remove hydrogen sulfide from hydrocarbon gas streams such as landfill gas, natural gas, and synthesis gas. Biodesulfurization offers environmental advantages, but still requires optimization and more insight in the reaction pathways and kinetics. We carried out experiments with gas lift bioreactors inoculated with haloalkaliphilic sulfide-oxidizing bacteria. At oxygen-limiting levels, that is, below an O(2)/H(2)S mole ratio of 1, sulfide was oxidized to elemental sulfur and sulfate. We propose that the bacteria reduce NAD(+) without direct transfer of electrons to oxygen and that this is most likely the main route for oxidizing sulfide to elemental sulfur which is subsequently oxidized to sulfate in oxygen-limited bioreactors. We call this pathway the limited oxygen route (LOR). Biomass growth under these conditions is significantly lower than at higher oxygen levels. These findings emphasize the importance of accurate process control. This work also identifies a need for studies exploring similar pathways in other sulfide oxidizers such as Thiobacillus bacteria.

Modelling of the biofiltration of reduced sulphur compounds through biotrickling filters connected in series: effect of H2S

Background: The behaviour of two biotrickling filters connected in serie (BTF) inoculated with Acidithiobacillus thiooxidans and Thiobacillus thioparus, biodegrading hydrogen sulphide (H2S) and dimethyl sulphide (DMS) simultaneously were studied. A model which considers gas to liquid mass transfer and biooxidation in the biofilm attached to the support is developed. Additionally, a fixed bed biotrickling filter where the microorganism is immobilized in a biofilm which degrades a mixture of H2S and DMS is implemented. Validation of the model was carried out using experimental data obtained at different H2S and DMS loads. Results: The inhibitory effect caused by the presence of H2S on the DMS is observed, which is evidenced by the decrease of the DMS removal efficiency from 80 to 27 percent, due to the preference that T. thioparus has by simple metabolism. H2S is not affected by the DMS, with removal efficiencies of 95 to 97 percent, but it decreases at high concentrations of the compound, due to the inhibition of metabolism by high H2S input loads. The model which describes the BFT fits successfully with the experimental results and it has a high sensitivity to inhibition parameters. Conclusion: It is shown that the microorganism has a high affinity for H2S, producing substrate inhibition when the concentration is high. The H2S is able to inhibit the DMS biooxidation, whereas the DMS does not affect the H2S biooxidation.

Microbial CO2 fixation potential in a tar-oil-contaminated porous aquifer.

CO(2) fixation is one of the most important processes on the Earth's surface, but our current understanding of the occurrence and importance of chemolithoautotrophy in the terrestrial subsurface is poor. Groundwater ecosystems, especially at organically polluted sites, have all the requirements for autotrophic growth processes, and CO(2) fixation is thus suggested to contribute significantly to carbon flux in these environments. We explored the potential for autotrophic CO(2) fixation in microbial communities of a petroleum hydrocarbon-contaminated aquifer by detection of functional marker genes (cbbL, cbbM), encoding different forms of the key enzyme RubisCO of the Calvin-Benson-Bassham cycle. Quantification of (red-like) cbbL genes revealed highest numbers at the upper fringe of the contaminant plume and the capillary fringe where reduced sulphur and iron species are regularly oxidized in the course of groundwater table changes. Functional gene sequences retrieved from this area were most closely related to sequences of different thiobacilli. Moreover, several cultures could be enriched from fresh aquifer material, all of which are able to grow under chemolithoautotrophic conditions. A novel, nitrate-reducing, thiosulfate-oxidizing bacterial strain, recently described as Thiobacillus thiophilus D24TN(T) sp. nov., was shown to carry and transcribe RubisCO large-subunit genes of form I and II. Enzyme tests proved the actual activity of RubisCO in this strain.

Transformation of heavy metals and the formation of secondary iron minerals during pig manure bioleaching by the co-inoculation acidophilic thiobacillus.

Bioleaching of heavy metals from pig manure using a mixture of harmless iron- and sulfur-oxidizing bacteria in an air-lift reactor was conducted. The transformation of heavy metals and the formation of secondary Fe minerals during bioleaching were also investigated in the present study. The removal efficiencies of Zn, Cu, and Mn from pig manure were 95.1%, 80.9%, and 87.5%, respectively. Zn mainly existed in the form of Fe-Mn oxides in fresh pig manure; most of the pig manure-borne Cu was in organic matter form; Mn existed mainly in Fe-Mn oxides, carbonates, and residual forms. The pig manure can be applied to land more safely after bioleaching because the heavy metals mainly existed in stable forms. The removal efficiencies Zn, Cu, and Mn had good relationships with pH and oxidation reduction potential during bioleaching. A mixture ofjarosite and schwertmannite was found in the bioleached pig manure, which might have an adverse effect on the solubilization efficiency of toxic metals from pig manure. The bioleaching process using a mixture of harmless iron- and sulfur-oxidizing bacteria was shown to be a very feasible technology for the removal of heavy metals from pig manure.

Expression patterns of mRNAs for methanotrophy and thiotrophy in symbionts of the hydrothermal vent mussel Bathymodiolus puteoserpentis.

The hydrothermal vent mussel Bathymodiolus puteoserpentis (Mytilidae) from the Mid-Atlantic Ridge hosts symbiotic sulfur- and methane-oxidizing bacteria in its gills. In this study, we investigated the activity and distribution of these two symbionts in juvenile mussels from the Logatchev hydrothermal vent field (14°45'N Mid-Atlantic Ridge). Expression patterns of two key genes for chemosynthesis were examined: pmoA (encoding subunit A of the particulate methane monooxygenase) as an indicator for methanotrophy, and aprA (encoding the subunit A of the dissimilatory adenosine-5'-phosphosulfate reductase) as an indicator for thiotrophy. Using simultaneous fluorescence in situ hybridization (FISH) of rRNA and mRNA we observed highest mRNA FISH signals toward the ciliated epithelium where seawater enters the gills. The levels of mRNA expression differed between individual specimens collected in a single grab from the same sampling site, whereas no obvious differences in symbiont abundance or distribution were observed. We propose that the symbionts respond to the steep temporal and spatial gradients in methane, reduced sulfur compounds and oxygen by modifying gene transcription, whereas changes in symbiont abundance and distribution take much longer than regulation of mRNA expression and may only occur in response to long-term changes in vent fluid geochemistry.

Thiosulphate oxidation by Thiobacillus thioparus and Halothiobacillus neapolitanus strains isolated from the petrochemical industry

Sulphur Oxidizing Bacteria (SOB) is a group of microorganisms widely used for the biofiltration of Total Reduced Sulphur compounds (TRS). TRS are bad smelling compounds with neurotoxic activity which are produced by different industries (cellulose, petrochemical). Thiobacillus thioparus has the capability to oxidize organic TRS, and strains of this bacterium are commonly used for TRS biofiltration technology. In this study, two thiosulphate oxidizing strains were isolated from a petrochemical plant (ENAP BioBio, Chile). They were subjected to molecular analysis by real time PCR using specific primers for T. thioparus. rDNA16S were sequenced using universal primers and their corresponding thiosulphate activities were compared with the reference strain T. thioparus ATCC 10801 in batch standard conditions. Real time PCR and 16S rDNA sequencing showed that one of the isolated strains belonged to the Thiobacillus branch. This strain degrades thiosulphate with a similar activity profile to that shown by the ATCC 10801 strain, but with less growth, making it useful in biofiltration.