Sulfur-oxidizing Activity Research Articles

Insights into the genome of Methylobacterium sp. NMS14P, a novel bacterium for growth promotion of maize, chili, and sugarcane.

A novel methylotrophic bacterium designated as NMS14P was isolated from the root of an organic coffee plant (Coffea arabica) in Thailand. The 16S rRNA sequence analysis revealed that this new isolate belongs to the genus Methylobacterium, and its novelty was clarified by genomic and comparative genomic analyses, in which NMS14P exhibited low levels of relatedness with other Methylobacterium-type strains. NMS14P genome consists of a 6,268,579 bp chromosome, accompanied by a 542,519 bp megaplasmid and a 66,590 bp plasmid, namely pNMS14P1 and pNMS14P2, respectively. Several genes conferring plant growth promotion are aggregated on both chromosome and plasmids, including phosphate solubilization, indole-3-acetic acid (IAA) biosynthesis, cytokinins (CKs) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, sulfur-oxidizing activity, trehalose synthesis, and urea metabolism. Furthermore, pangenome analysis showed that NMS14P possessed the highest number of strain-specific genes accounting for 1408 genes, particularly those that are essential for colonization and survival in a wide array of host environments, such as ABC transporter, chemotaxis, quorum sensing, biofilm formation, and biosynthesis of secondary metabolites. In vivo tests have supported that NMS14P significantly promoted the growth and development of maize, chili, and sugarcane. Collectively, NMS14P is proposed as a novel plant growth-promoting Methylobacterium that could potentially be applied to a broad range of host plants as Methylobacterium-based biofertilizers to reduce and ultimately substitute the use of synthetic agrochemicals for sustainable agriculture.

Biogeochemical impacts of fish farming on coastal sediments: Insights into the functional role of cable bacteria.

Fish farming in sea cages is a growing component of the global food industry. A prominent ecosystem impact of this industry is the increase in the downward flux of organic matter, which stimulates anaerobic mineralization and sulfide production in underlying sediments. When free sulfide is released to the overlying water, this can have a toxic effect on local marine ecosystems. The microbially-mediated process of sulfide oxidation has the potential to be an important natural mitigation and prevention strategy that has not been studied in fish farm sediments. We examined the microbial community composition (DNA-based 16S rRNA gene) underneath two active fish farms on the Southwestern coast of Iceland and performed laboratory incubations of resident sediment. Field observations confirmed the strong geochemical impact of fish farming on the sediment (up to 150 m away from cages). Sulfide accumulation was evidenced under the cages congruent with a higher supply of degradable organic matter from the cages. Phylogenetically diverse microbes capable of sulfide detoxification were present in the field sediment as well as in lab incubations, including cable bacteria (Candidatus Electrothrix), which display a unique metabolism based on long-distance electron transport. Microsensor profiling revealed that the activity of cable bacteria did not exert a dominant impact on the geochemistry of fish farm sediment at the time of sampling. However, laboratory incubations that mimic the recovery process during fallowing, revealed successful enrichment of cable bacteria within weeks, with concomitant high sulfur-oxidizing activity. Overall our results give insight into the role of microbially-mediated sulfide detoxification in aquaculture impacted sediments.

Carbon Assimilation by the Picoplanktonic Community Inhabiting the Secondary Chlorophyll Maximum of the Anoxic Marine Zones of the Eastern Tropical North and South Pacific

Anoxic marine zones (AMZs) constitute pelagic systems distinguished from the oxygen minimum zones (OMZs) by the complete absence of detectable oxygen and the accumulation of nitrite in mid-waters. At the top of the oxygen-depleted layer and below the oxycline, nutrients are abundant; light intensity is very much reduced (<1% of incident light) and a secondary chlorophyll maximum (SCM) is developed. The shoaling of the oxygen-depleted layer, product of the AMZ expansion, could enhance this SCM, which has little-known biogeochemical effects. Here, we show that the SCM is contributing a measurable signal in the particulate organic carbon (POC), enough to alter the δ13CPOC in the top of the oxygen-depleted layer. This data showed significant differences among stations with and without the development of a SCM, being 3.0‰ heavier when a SCM is developed, and indicating photosynthetic activity and/or remineralization in the top of the AMZ. More depleted δ13CPOC values were also found when no SCM was present indicating stronger chemoautotrophic activity, potentially driven by anammox and sulfur-oxidizing bacteria activity. Assimilation rate data show that when sufficient light and Prochlorococcus are present, photosynthesis exceeds chemoautotrophic carbon fixation, and can exceed heterotrophic assimilation of glucose or acetate. However, in the majority of the stations, assimilation rates of both glucose and acetate exceeded carbon fixation rates under light stimulation, suggesting that often the SCM is still a net heterotrophic system.

Biolixiviación de metales a partir de residuos de procesos de mecanizado

The present study evaluates the ability of Acidithioobacillus thiooxidans DSM 26636 to grow and leach metals from industrial wastes (IW) containing different metal compositions, coded as IW-steel and IW-scrap. For this purpose, biolixiviation processes were assessed during 21 days at 30°C and 150 rpm, with 1% (w/v) of IW pulp density. Microbial growth was evaluated periodically by measuring sulfates´ production; pH and sulfuric acid concentration were also monitored, and metal bioleaching was evaluated by ICP-OES. Results showed that A. thiooxidans sulfur-oxidizing activity was higher in the presence of IW-steel. Specifically, sulfates and sulfuric acid production in IW-steel corresponded to 21,524 mg/L and 0.096 M, respectively, with a pH diminution to 1.54. In the case of IW-scrap, sulfates´ production only increased to up to 4392 mg/L at day 21, and not so significant changes were observed in pH and sulfuric acid concentration. Besides, metal removal was higher in IW-steel, being Fe > Mn > Mg ≥ Zn ≥ Cu > Cr ≥ Ni. The results obtained reinforce the fact that A. thiooxidans DSM 26636 presents an elevated potential to be employed in biotreatment processes, and that its biolixiviation efficiency strongly depends on the metal content present in the residues.

Sulfate-Reducing and Sulfur-Oxidizing Bacterial Activity in the Coastal Waters of Arabian Sea During Post Upwelling Season

The synergistic existence of sulfate-reducing bacteria (SRB) and colorless sulfur-oxidizing bacteria (CSOB) involved in nutrient turnover is sparsely documented in coastal waters. To understand the processes mediated by these physiological groups we proposed to analyze their abundance and activities and the extent of interaction with various environmental parameters. Therefore, water samples were collected during post upwelling phase off Calicut and Kochi in August 2008. Stations at 30 m, 50 m, 100 m water depths were considered as nearshore, and those at 300 m and 500 m were considered as offshore. Maximum sulfate-reducing activity (SRA) of 86 nM d−1 was in the nearshore surface waters of Kochi and 30 nM d−1 in offshore bottom waters of Calicut. In these waters, SRA was dictated by total suspended load and phaeophytin, respectively. Maximum number of CSOB of 1.76 × 106 cells l−1 was detected in the surface waters of both the stations. At both nearshore and offshore waters of Kochi and Calicut, CSOB related to the sulfur-oxidizing activity (SOA) which ranged from 3 to 577 µM d−1 and 3 to 223 µM d−1, respectively. This paper elucidates the coupling between SRB and CSOB and their contribution towards nutrient regeneration and restoration of homeostasis during the waning phase of upwelling in these coastal waters.

Comparative genomic and metabolic analysis of manganese-oxidizing mechanisms in Celeribacter manganoxidans DY25T: Its adaptation to the environment of polymetallic nodules

Manganese (Mn) nodule is one of the ubiquitous polymetallic concretions and mainly consists of Mn − Fe oxi-hydroxide precipitations. A primary oxidation of Mn(II) to MnO2, in which microorganisms may play important roles, is followed by agglomeration of MnO2 into nodules. Celeribater manganoxidans DY25T, belonging to family Rhodobacteraceae, has ability to catalyze the formation of MnO2 [1]. The concentration of MnO2 formed by harvested cells reached 7.08 μM after suspended in 10 mM HEPES (pH 7.5). Genomic and physiological characteristics of strain DY25T provided a better understanding of its Mn-oxidizing mechanism. Fifteen genes (including four multicopper oxidases) may be involved in Mn(II)-oxidation, whereas only three of them can promote this process. Sulfur-oxidizing activity was detected, which may be associated with manganese oxidation. Genes involved in import and export of primary elemental ingredients (C, N, P and S) and metallic elements (e.g. Mn) were discovered, demonstrating its potential roles in the biogeochemical cycle.

Influence of Dissolved-Aluminum Concentration on Sulfur-Oxidizing Bacterial Activity in the Biodeterioration of Concrete.

Several studies undertaken on the biodeterioration of concrete sewer infrastructures have highlighted the better durability of aluminate-based materials. The bacteriostatic effect of aluminum has been suggested to explain the increase in durability of these materials. However, no clear demonstration of the negative effect of aluminum on cell growth has been yet provided in the literature. In the present study, we sought to investigate the inhibitory potential of dissolved aluminum on nonsterile microbial cultures containing sulfur-oxidizing microorganisms. Both kinetic (maximum specific growth rate) and stoichiometric (oxygen consumption yield) parameters describing cells activity were accurately determined by using respirometry measurements coupled with modeled data obtained from fed-batch cultures run for several days at pH below 4 and with increasing total aluminum (Altot) concentrations from 0 to 100 mM. Short-term inhibition was observed for cells poorly acclimated to high salinity. However, inhibition was significantly attenuated for cells grown on mortar substrate. Moreover, after a rapid adaptation, and for an Altot concentration up to 100 mM, both kinetic and stoichiometric growth parameters remained similar to those obtained in control culture conditions where no aluminum was added. This argued in favor of the impact of ionic strength change on the growth of sulfur-oxidizing microorganism rather than an inhibitory effect of dissolved aluminum. Other assumptions must therefore be put forward in order to explain the better durability of cement containing aluminate-based materials in sewer networks. Among these assumptions, the influence of physical or chemical properties of the material (phase reactivity, porosity, etc.) might be proposed.IMPORTANCE Biodeterioration of cement infrastructures represents 5 to 20% of observed deteriorations within the sewer network. Such biodeterioration events are mainly due to microbial sulfur-oxidizing activity which produces sulfuric acid able to dissolve cementitious material. Calcium aluminate cement materials are more resistant to biodeterioration compared to the commonly used Portland cement. Several theories have been suggested to describe this resistance, and the bacteriostatic effect of aluminum seems to be the most plausible explanation. However, results reported by the several studies on this exact topic are highly controversial. This present study provides a comprehensive analysis of the influence of dissolved aluminum on growth parameters of long-term cultures of sulfur-oxidizing bacterial consortia sampled from different origins. Kinetic and stoichiometric parameters estimated by respirometry measurements and modeling showed that total dissolved-aluminum concentrations up to 100 mM were not inhibitory, but it is more likely that a sudden increase in the ionic strength affects cell growth. Therefore, it appears that the bacteriostatic effect of aluminum on microbial growth cannot explain the better durability of aluminate based cementitious materials.

Spatio-temporal variations in sulfur-oxidizing and sulfate-reducing bacterial activities during upwelling, off south-west coast of India

Summary The Arabian Sea, off SW India, is becoming more anoxic in recent years. Poor ventilation affects microbial degradation of organic matter in the oxygen minimum zone (≤2.85 ml l−1 O2, ≤0.02 μM NO2) and the anoxic marine zone (≤0.09 ml l−1 O2, ≥0.5 μM NO2). We posit that one of the reasons at the microbial level could be due to a more prominent increase in sulfate-reducing activity (SRA), than sulfur-oxidizing activity (SOA). Hence, the objective was to measure the extent to which SOA can counter the effect of SRA. We, therefore examined these activities along with relevant environmental variables from 2009 to 2011 off Kochi (9.55°N–75.33°E) and Trivandrum (8.26°N–76.50°E), covering the three phases of upwelling. SRA was measured radiometrically using 35S, and SOA by iodometry. Off Kochi, the SOA of the water column increased 6× (194–1151 μM d−1) and SRA 4× (13–54 nM d−1) from phase I to III. Off Trivandrum, the increase in SOA was 1.7× (339–560 μM d−1) and SRA 7× (24–165 nM d−1) contributing to the build-up of reducing/oxidizing conditions. This increase in SOA moderates the effect of increase in SRA. Besides, the average concentrations of dissolved oxygen and nitrite off Trivandrum were 1.80 ± 1.66, 1.48 ± 1.55, 1.93 ± 1.86 ml l−1 and 0.14 ± 0.14, 1.69 ± 0.67, 0.34 ± 0.42 μM during the three phases respectively. Hence, it is suggested that the coastal waters examined in this study could probably be between oxygen minimum zone (OMZ) and anoxic minimum zone (AMZ) in patches temporarily. The present paper highlights the interactions between sulfate-reducing and sulfur-oxidizing activities, during upwelling for the first time in these waters. These observations give an important and timely insight into the implications.

Decline in Sulfate Reducing Bacterial Consortia by the Sulfur Oxidizing Bacterial Activity

In anaerobic environment, dominant sulfate reducing bacteria (SRB) consortia are found to cause many serious problems to the oil such as sour oil, hydrogen sulfide (H2S), and metal corrosion. They are obligatory anaerobes using sulfate, thiosulfate and sulfites as final electron acceptors and use organic acids or alcohols as a carbon source. In the aerobic system, other dominant niches are sulfur-oxidizing bacteria (SOB) playing role in biological oxidation of hydrogen sulfide. These SOB convert H2S into elemental sulfur (S0) by partial oxidation. Since the levels of reduction and oxidation are dependent on the oxygen concentration. In the condition of limited oxygen, sulfate generated by SOB can also be contributed to the reduction of oxygen which encourages SRB proliferation in anaerobic environment. In this research, we were interested to manage the conditions to control the dominant niches by management of oxygen levels. In the experiment, the concentration of sulfate concentration, acidity, sulfide were determined to understand the microbial activity. The results showed after cocultures of SRB and SOB niches in the present of oxygen, the activity of SRB was prevented since a decrease in H2S product but an increase in sulfate concentration were observed. This revealed a promising niches of SOB isolates in the presence of oxygen and active in high sulfide removal. These data indicated the situation suitable for either SOB or SRB community is dependent on oxygen concentration. The management of SOB community can be used as an alternative method to remove contaminating H2S from the system.

Evaluation of biogeochemical reactivity of fresh and weathered contaminated dredged sediments

Metal mobility in contaminated marine sediments is largely controlled by low-soluble sulfides. In dredged sediments exposed to air and water, geochemical and microbial-mediated processes may enhance the weathering and leaching of hazardous contaminants, especially trace metals. The objective of the present study was to thoroughly characterize and assess the biogeochemical reactivity of marine-dredged sediments. Two samples of dredged sediments, one stored (to preserve anoxic conditions) and another exposed to the air, were assessed in the perspective of their long-term management. Biogeochemical reactivity was evaluated, especially by a qualitative assessment of aerobic iron- and sulfur-oxidizing bacteria activity. Despite the high content of total sulfides (2 to 3.5 wt.% S), the acid-volatile fraction was low (4.3 × 10−3 vs. 9.4 × 10−5 g S kg−1 in raw and weathered sediments, respectively), as an indication of the high degree of crystallinity of sulfide minerals present in samples. The raw sediment was reactive, particularly to aerobic bacteria that decreased the pH from 7.0 to 4.2, for neutrophilic sulfur-oxidizing bacteria, and from 4.5 to 2.5, for acidophilic iron-oxidizing, within only 18 days. Even though only neutrophilic sulfur-oxidizing bacteria seem reactive in the aged sediment, they countered the major buffering effect due to the high amount of carbonates. Important differences in the temporal evolution of pH and Eh of the raw and aged sediments support these results. Neutrophilic sulfur-oxidizing bacteria showed to be the most reactive in both sediments. Finally, despite the sharp pH decrease over time, acidophilic bacteria activity does not seem to be particularly enhanced.

Transformation of galena to pyromorphite produces bioavailable sulfur for neutrophilic chemoautotrophy.

The aqueous concentration of lead [Pb(II)] in geochemical environments is controlled by the solubility of Pb-bearing minerals and their weathering products. In contaminated soils, a common method for in situ stabilization of Pb(II) is the addition of phosphate to convert more redox sensitive sulfide minerals into sparingly soluble pyromorphite [Pb5 (PO4 )3 X]. In this study, we conducted experimental studies to investigate the fate of reduced sulfur during the conversion of galena [PbS] to chloropyromorphite [Pb5 (PO4 )3 Cl]. Powder X-ray diffraction analysis indicated that the reaction of phosphate with galena under oxic conditions resulted in the oxidation of sulfide and formation of elemental sulfur [S8 ]. Under oxic abiotic conditions, the S8 was retained in the solid phase, and negligible concentrations of sulfur as sulfide and thiosulfate were detected in the aqueous phase and only a small amount of sulfate. When PbS reacted in the presence of the chemoautotrophic organism Bosea sp. WAO, the S8 in the secondary mineral was oxidized to sulfate. Strain WAO produced significantly more sulfate from the secondary S8 than from the primary galena. Microscopic analysis of mineral-microbe aggregates on mineral-embedded slide cultures showed that the organism was colocalized and increased in biomass over time on the secondary mineral surface supporting a microbial role. The results of this study indicate that stimulation of sulfur-oxidizing activity may be a direct consequence of phosphate amendments to Pb(II)-contaminated soils.

An innovative approach to reproduce the biodeterioration of industrial cementitious products in a sewer environment. Part I: Test design

A test method to evaluate biogenic resistance of cementitious pipe products intended for sewer networks is presented. It consisted in inoculating pipes with a highly diverse microbial consortium (urban wastewater treatment plant), and trickling a feeding solution containing a safe and soluble reduced sulfur source, thiosulfate, over the inoculated surface in order to select a sulfur-oxidizing activity. Thiosulfate was used in the form of an aqueous solution, which facilitated the monitoring of (i) the bacterial activity by sulfur mass balances in the liquid phase, and thus quantification of acid production, and of (ii) the leaching of cementitious ions. Cement-based linings made of (i) blast furnace slag cement and (ii) calcium aluminates cement were tested. Results showed the selection of sulfur-oxidizing bacteria and the production of biogenic acid. Differences were shown between the linings in terms of Ca and Al dissolution. Biomass characterization highlighted the influence of the lining composition on colonization.

Growth of acidophilic chemolithotrophic microbial communities and sulfur oxidation in the presence of coal ashes

Out of two communities of acidophilic chemolithotrophic microorganisms (ACM), a mesophilic and a thermophilic ones, the latter was selected due to its higher rate of sulfur oxidation and pH decrease to >1 in the presence of coal ashes (CA). The structure of ACM communities was retained. Sulfur-oxidizing activity of the microorganisms from the thermophilic community was observed at pH from 1.8 to 2.6 at sulfur concentrations of 0.6–1.0%. Efficient production of acidic solutions with pH 0.69–0.86 was observed after single CA introduction in the amount corresponding to 5–30% pulp density and in the course of pulp density increasing daily from 1 to 50%. Leaching of rare earth elements from 30% coal ash pulp (pH 0.76) was 15 to 30% of their initial content. No sorption of metals on the biomass was observed.

Accelerated test design for biodeterioration of cementitious materials and products in sewer environments

A new test method for evaluating the resistance of cementitious products and materials to biogenic acid attack has been developed. It consists of inoculating pipes with a highly diverse microbial consortium (from an urban wastewater treatment plant), and trickling a feeding solution containing a safe and soluble reduced sulfur source over the inoculated surface in order to select a sulfur-oxidizing activity. A sulfur substrate, thiosulfate, was used in the feeding solution, which facilitated the monitoring of the bacterial activity, and of the leaching of cementitious ions. The functioning of the test in terms of selection of sulfur oxidizing microorganisms, acid and sulfate production, and degradation mechanisms occurring in the cementitious materials has been validated previously. This paper aims (i) to evaluate the reproducibility and repeatability of the test when the source of the sludge used for the inoculation is changed and (ii) to optimize the test design. The following changes were carried out with a view to intensifying the biological and chemical reactions: change of sulfur substrate (tetrathionate instead of thiosulfate), increased sulfur flow rate at the surface of the biofilm, and increased temperature. The results highlight good reproducibility of the test: the change in the inoculum and in the sulfur substrate led to the same phenomena in terms of (i) transformation of reduced sulfur species into sulfate and production of acid and (ii) degradation mechanisms of the cement linings. Moreover, the change of the sulfur substrate combined with the reduction of the exposed surface locally intensified the alteration kinetics. In contrast, in the experimental conditions, the increase in temperature did not seem to have any positive influence on the microbial activity.

Effect of mixed moderately thermophilic adaptation on leachability and mechanism of high arsenic gold concentrate in an airlift bioreactor

A refractory gold concentrate with 19% arsenic was treated by a mixed moderately thermophiles in an airlift bioreactor through an adaptation protocol. The moderately thermophiles could respond well to 20% (w/v) pulp density with less than 10% loss of productivity, and resist arsenic up to 15 g/L. There were a lot of jarosite, arsenolite and sulfur, but not scorodite and ferric arsenate in the bioleached residue. Jarosite passivation and lower sulfur-oxidizing activity of the cells due to the toxicity of the high concentrations of soluble arsenic and iron ions at low pH value should mainly response for the incomplete extraction at high pulp density. The initial bacterial community did not change in nature except for new found P aeruginosa ANSC, but sulfur-oxidizing microorganisms have been dominant microorganisms after a long time of adaptation. Pseudomonas aeruginosa originating from the gold concentrate should be closely relative to the metabolism of the organic matters contained in the refractory gold concentrate.

Microbial treatment of sulfur-contaminated industrial wastes

The present study evaluated the microbial removal of sulfur from a solid industrial waste in liquid culture under laboratory conditions. The study involved the use of two bacteria Acidithiobacillus ferrooxidans ATCC 53987 and Acidithiobacillus thiooxidans AZCT-M125-5 isolated from a Mexican soil. Experimentation for industrial waste biotreatment was done in liquid culture using 125-mL Erlenmeyer flasks containing 30 mL Starkey modified culture medium and incubated at 30°C during 7 days. The industrial waste was added at different pulp densities (8.25–100% w/v) corresponding to different sulfur contents from 0.7 to 8.63% (w/w). Sulfur-oxidizing activity of the strain AZCT-M125-5 produced 281 and 262 mg/g of sulfate and a sulfur removal of 60% and 45.7% when the pulp density was set at 8.25 and 16.5% (w/v), respectively. In comparison, the strain A. ferrooxidans ATCC 53987 showed a lower sulfur-oxidizing activity with a sulfate production of 25.6 and 12.7 mg/g and a sulfur removal of 6% and 2.5% at the same pulp densities, respectively. Microbial growth was limited by pulp densities higher than 25% (w/v) of industrial waste with minimal sulfur-oxidizing activity and sulfur removal. The rate of sulfur removal for Acidithiobacillus thioxidans AZCT-M125-5 and Acidithiobacillus ferrooxidans ATCC 53987 was 0.185 and 0.0159 mg S g−1 h−1 with a pulp density of 16.5% (w/v), respectively. This study demonstrated that Acidithiobacillus thiooxidans AZCT-M125-5 possesses a high sulfur-oxidizing activity, even at high sulfur concentration, which allows the treatment of hazardous materials.

Cell-Specific Thioautotrophic Productivity of Epsilon-Proteobacterial Epibionts Associated with Shinkaia crosnieri

In this study, we report experimental evidence of the thioautotrophic activity of the epibiotic microbial community associated with the setae of Shinkaia crosnieri, a galatheid crab that is endemic to deep-sea hydrothermal systems in the Okinawa Trough in Japan. Microbial consumption of reduced sulfur compounds under in situ hydrostatic and atmospheric pressure provided evidence of sulfur-oxidizing activity by the epibiotic microbial community; the rate of sulfur oxidation was similar under in situ and decompressed conditions. Results of the microbial consumption of reduced sulfur compounds and tracer experiments using 13C-labeled bicarbonate in the presence and absence of thiosulfate (used as a thioautotrophic substrate) convincingly demonstrated that the epibiotic microbial community on S. crosnieri drove primary production via an energy metabolism that was coupled with the oxidation of reductive sulfur compounds. A combination of tracer experiments, fluorescence in situ hybridization (FISH) and nano-scale secondary ion mass spectrometry (Nano-SIMS) indicated that the filamentous cells of the genus Sulfurovum belonging to the class Epsilonproteobacteria were thioautotrophs in the epibiotic community of S. crosnieri. In conclusion, our results strongly suggest that thioautotrophic production by Sulfurovum members present as the epibiotic microbial community play a predominant role in a probable nutritional ectosymbiosis with S. crosnieri.

Evaluation of haloalkaliphilic sulfur-oxidizing microorganisms with potential application in the effluent treatment of the petroleum industry

Haloalkaliphilic sulfur-oxidizing mixed cultures for the treatment of alkaline-saline effluents containing sulfide were characterized and evaluated. The mixed cultures (IMP-PB, IMP-XO and IMP-TL) were obtained from Mexican alkaline soils collected in Puebla (PB), Xochimilco (XO) and Tlahuac (TL), respectively. The Ribosomal Intergenic Spacer Analysis (RISA) revealed bacteria related to Thioalkalibacterium and Thioalkalivibrio in IMP-XO and IMP-PB mixed cultures. Halomonas strains were detected in IMP-XO and IMP-TL. In addition, an uncultured Bacteroides bacterium was present in IMP-TL. Mixed cultures were evaluated at different pH and NaCl concentrations at 30°C. IMP-PB and IMP-TL expressed thiosulfate-oxidizing activity in the 7.5-10.5 pH range, whereas IMP-XO presented its maximal activity with 19.0 mg O₂ g (protein)⁻¹ min⁻¹, at pH 10.6; it was not affected by NaCl concentrations up to 1.7 M. In continuous culture, IMP-XO showed a growth rate of 15 day⁻¹, productivity of 433.4 mg(protein) l⁻¹ day⁻¹ and haloalkaliphilic sulfur-oxidizing activity was also detected up to 170 mM by means of N-methyl-diethanolamine (MDEA). Saline-alkaline soil samples are potential sources of haloalkaliphilic sulfur-oxidizing bacteria and the mixed cultures could be applied in the treatment of inorganic sulfur compounds in petroleum industry effluents under alkaline-saline conditions.

Removal of hydrogen sulfide by sulfate-resistant Acidithiobacillus thiooxidans AZ11

Toxic H2S gas is an important industrial pollutant that is applied to biofiltration. Here, we examined the effects of factors such as inlet concentration and space velocity on the removal efficiency of a bacterial strain capable of tolerating high sulfate concentrations and low pH conditions. We examined three strains of Acidithiobacillus thiooxidans known to have sulfur-oxidizing activity, and identified strain AZ11 as having the highest tolerance for sulfate. A. thiooxidans AZ11 could grow at pH 0.2 in the presence of 74 g l(-1) sulfate, the final oxidation product of elemental sulfur, in the culture broth. Under these conditions, the specific sulfur oxidation rate was 2.9 g-S g-DCW (dry cell weight)(-1) d(-1). The maximum specific sulfur oxidation rate of A. thiooxidans AZ11 was 21.2 g-S g-DCW(-1) d(-1), which was observed in the presence of 4.2 g-SO4(2-) l(-1) and pH 1.5, in the culture medium. To test the effects of various factors on biofiltration by this strain, A. thiooxidans AZ11 was inoculated into a porous ceramic biofilter. First, a maximum inlet loading of 670 g-S m(-3) h(-1) was applied with a constant space velocity (SV) of 200 h(-1) (residence time, 18 s) and the inlet concentration of H2S was experimentally increased from 200 ppmv to 2200 ppmv. Under these conditions, less than 0.1 ppmv H2S was detected at the biofilter outlet. When the inlet H2S was maintained at a constant concentration of 200 ppmv and the SV was increased from 200 h(-1) to 400 h(-1) (residence time, 9 s), an H2S removal of 99.9% was obtained. However, H2S removal efficiencies decreased to 98% and 94% when the SV was set to 500 h(-1) (residence time, 7.2 s) and 600 h(-1) (residence time, 6 s), respectively. The critical elimination capacity guaranteeing 96% removal of the inlet H2S was determined to be 160 g-S m(-3) h(-1) at a space velocity of 600 h(-1). Collectively, these findings show for the first time that a sulfur oxidizing bacterium has a high sulfate tolerance and a high sulfur oxidizing activity below pH 1.

Simultaneous removal of H 2S and NH 3 in biofilter inoculated with Acidithiobacillus thiooxidans TAS

H2S and NH3 gases are toxic, corrosive and malodorous air pollutants. Although there are numerous well-established physicochemical techniques presently available for the treatment of these gases, the growing demand for a more economical and improved process has prompted investigations into biological alternatives. In biological treatment methods, H2S is oxidized to SO4(2-) by sulfur-oxidizing bacteria, and then NH3 is removed by chemical neutralization with SO4(2-) to (NH4)2SO4. Since the accumulated (NH4)2SO4 can inhibit microbial activity, it is important to utilize an effective sulfur-oxidizing bacterium that has tolerance to high concentrations of (NH4)2SO4 for the simultaneous removal of H2S and NH3. In this study, a sulfur-oxidizing bacterium with tolerance to high concentrations of (NH4)2SO4 was isolated from activated sludge and identified as Acidithiobacillus thiooxidans TAS. A. thiooxidans TAS could display its sulfur-oxidizing activity in a medium supplemented with 60 g.l(-1) (NH4)2SO4, even though its growth and sulfur-oxidizing activity were completely inhibited in 80 g.l(-1) (NH4)2SO4. When H2S alone was supplied to a ceramic biofilter inoculated with A. thiooxidans TAS, an almost 100% H2S removal efficiency was maintained until the inlet H2S concentration was increased up to 900 microl.l(-1) and the space velocity up to 500 h(-1), at which the amount of H2S eliminated was 810 g-S.m(-3).h(-1). However, when NH3 (50-500 microl.l(-1)) was simultaneously supplied to the biofilter with H2S, the maximum amount of H2S eliminated decreased to 650 g-S.m(-3).h(-1). The inhibition of H2S removal by low NH3 concentrations (50-200 microl.l(-1)) was similar to that by high NH3 concentrations (300-500 microl.l(-1)). The critical inlet H2S load that resulted in over 99% removal was determined as 400 g-S.m(-3).h(-1) in the presence of NH3.