Invasion mechanism of Spartina alterniflora by regulating soil sulfur and iron cycling and microbial composition in the Jiuduansha Wetland

Spartina alterniflora, an invasive plant widely distributed in China's coastal regions, has had a significant impact on the stability of wetland ecosystems and elemental biogeochemical cycles. The invasion of S. alterniflora has been found to lead to the accumulation of sulfides in the soil. The cycling of sulfur and iron in the soil is closely interconnected. Coastal estuarine wetlands are influenced by both freshwater in rivers and seawater tides, as well as the frequent variations in redox conditions caused by tidal fluctuations, which makes the cycling of sulfur and iron in the soil invaded by S. alterniflora more intricate. In this study, field surveys and laboratory experiments were conducted to explore the effects of S. alterniflora invasion and hydrological changes on the cycling of sulfur and iron as well as related functional microorganisms in the soil. The invasion of S. alterniflora showed an increase in soil reduced inorganic sulfur (RIS) components in both high and low marshes of Jiuduansha wetland, with higher content observed in summer and autumn. The tidal simulation experiments revealed abundant sulfate in seawater tidal conditions could promote the formation of acid volatile sulfides (AVS) in the soil of low marshes invaded by S. alterniflora and ensuring the continuous increase in AVS content. Diffusive gradients in-thin-films (DGT) technology indicated the existence of high-concentration soluble S2- enrichment zones in the soil of low marshes invaded by S. alterniflora, which may be related to S. alterniflora root exudates. Tidal action increased the relative abundance of sulfur-reducing bacteria (SRB) in the soil of low marshes, and under the influence of seawater tidal action, SRB exhibited higher relative abundance. However, S. alterniflora might inhibit the activity of iron-reducing bacteria (FeRB) in the soil of low marshes. In conclusion, S. alterniflora may enhance the sulfate reduction rate and promote the formation of free sulfides in tidal salt marsh ecosystems by releasing root exudates that stimulate the activity of SRB, while concurrently inhibiting the activity of FeRB and reducing their competition with SRB. This effect is particularly pronounced in low marshes under seawater tidal conditions. Thus, S. alterniflora is capable of rapidly invading tidal salt marshes by utilizing sulfides effectively.

Association Between the Sulfur Microbial Diet and Risk of Colorectal Cancer

IMPORTANCE

Sulfur-metabolizing bacteria that reduce dietary sulfur to hydrogen sulfide have been associated with colorectal cancer (CRC). However, there are limited studies investigating the association between diet and sulfur-metabolizing bacteria in the development of CRC.

OBJECTIVE

To develop a dietary score that correlates with gut sulfur-metabolizing bacteria and to examine its association with CRC risk.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study included data from the Health Professionals Follow-up Study (1986-2014), Nurses' Health Study (1984-2016), and Nurses' Health Study II (1991-2017). Participants were US male health professionals and female registered nurses who were free of inflammatory bowel disease and cancer at baseline, with a subsample of participants who provided stool samples from 2012 to 2014. Statistical analysis was conducted from September 1, 2020, to June 1, 2021.

EXPOSURE

A dietary pattern, assessed by a food-frequency questionnaire, that most correlated with 43 sulfur-metabolizing bacteria identified through taxonomic and functional profiling of gut metagenome data.

MAIN OUTCOMES AND MEASURES

Incident CRC.

RESULTS

Among 214 797 participants comprising 46 550 men (mean [SD] age at baseline, 54.3 [9.7] years) and 168 247 women (mean [SD] age at baseline, 43.0 [9.2] years), 3217 incident cases of CRC (1.5%) were documented during 5 278 048 person-years of follow-up. The sulfur microbial diet, developed in a subsample of 307 men (mean [SD] age, 70.5 [4.3] years) and 212 women (mean [SD] age, 61.0 [3.8] years), was characterized by high intakes of low-calorie beverages, french fries, red meats, and processed meats and low intakes of fruits, yellow vegetables, whole grains, legumes, leafy vegetables, and cruciferous vegetables. After adjustment for other risk factors, greater adherence to the sulfur microbial diet was associated with an increased risk of CRC, with a hazard ratio (HR) of 1.27 (95% CI, 1.12-1.44) comparing the highest vs the lowest quintile of the diet score (linear trend of diet score quintiles; P < .001 for trend). When assessed by anatomical subsites, greater adherence to the sulfur microbial diet was positively associated with distal CRC (HR, 1.25; 95% CI, 1.05-1.50; P = .02 for trend) but not proximal colon cancer (HR, 1.13; 95% CI, 0.93-1.39; P = .19 for trend).

CONCLUSIONS AND RELEVANCE

Adherence to the sulfur microbial diet was associated with an increased risk of CRC, suggesting a potential mediating role of sulfur-metabolizing bacteria in the associaton between diet and CRC. Further research is needed to confirm these findings and to determine the underlying mechanisms.

Removal of heavy metals using a novel sulfidogenic AMD treatment system with sulfur reduction: Configuration, performance, critical parameters and economic analysis

A novel sulfidogenic acid mine drainage (AMD) treatment system with a sulfur reduction process was developed. During the 220-d operation, >99.9% of 380-mg/L ferric, 150-mg/L aluminum, 110-mg/L zinc, 20-mg/L copper and 2.5-mg/L lead ions, and 42.6-44.4% of 100-mg/L manganese ions in the synthetic AMD were step-by-step removed in the developed system with three pre-posed metal precipitators and a sulfur reduction reactor. Among them, zinc, copper and lead ions were removed by the biogenic hydrogen sulfide that produced through elemental sulfur reduction; while ferric, aluminum and manganese ions were removed by the alkali precipitation. Compared with the reported sulfate reduction reactors, the sulfur reduction reactor significantly reduced the chemical cost by 25.6-78.9% for sulfide production, and maintained a high sulfide production rate (1.12 g S^2-/L-d). The pH level in the sulfidogenic reactor driven by sulfur-reducing bacteria posed a significant effect on the sulfide production rate. Under a nearly neutral condition (pH 7.0-7.5), elemental sulfur dissolved into polysulfide to increase the bioavailability of S⁰. At acidic conditions (pH < 6.0), polysulfide formation was limited and sulfate reduction became dominant. Therefore, maintaining the sulfidogenic reactor driven by sulfur-reducing bacteria at neutral condition is essential to realize high-rate and low-cost AMD treatment. Moreover, the escape of residual hydrogen sulfide from the system was eliminated by employing a 17% recirculation from effluent to the sulfidogenic reactor.

A novel biological sulfur reduction process for mercury-contaminated wastewater treatment

The sulfidogenic process driven by sulfate-reducing bacteria (SRB) is not suitable for mercury-contaminated wastewater treatment due to the highly toxic methyl-mercury (MeHg) produced by SRB. In our previous study, we observed in short-term batch tests that sulfur-reducing bacteria (S⁰RB) could remove mercury ions without MeHg production. Thus, the aim of this study is to develop a biological sulfur reduction process driven by S⁰RB for mercury-contaminated wastewater, and investigate its long-term performance on mercury removal and MeHg accumulation. Receiving mercury-contaminated wastewater containing 0-50 mg Hg(II)/L for 326 days, S⁰RB in the sulfur-reducing bioreactor showed high tolerance with mercury toxicity, and removed 99.4% ± 1.4% of the influent Hg(II) by biogenic sulfide. MeHg was always found to be undetectable in the bioreactor, even though the sulfidogenic bacteria were exposed to high levels of Hg(II) in long-term trials. The result of qPCR analysis further revealed that the mercury-methylation functional gene (hgcA) concentration in the bioreactor sludge was found to be extremely lower than in the SRB-enriched sludge, Geobacter sulfurreducens PCA and Desulfomicrobium baculatum DSM 4028, implying that there was no or few mercury methylators in the bioreactor. In short, the biological sulfur reduction process using S⁰RB can efficiently treat mercury-contaminated wastewater, with high Hg(II) removal efficiency and no MeHg accumulation.

Arsenite removal without thioarsenite formation in a sulfidogenic system driven by sulfur reducing bacteria under acidic conditions

Sulfidogenic process using sulfate-reducing bacteria (SRB) has been used to remove arsenite from the arsenic-contaminated waters through the precipitation of arsenite with sulfide. However, excessive sulfide production and significant pH increase induced by sulfate reduction result in the formation of the mobile thioarsenite by-products and the inefficiency and instability of arsenite removal, especially when the arsenite level fluctuates. In this study, we proposed a novel sulfidogenic process driven by sulfur reducing bacteria (S⁰RB) for the arsenite removal under acidic conditions. In a long term experiment, efficient sulfide production (0.42 ± 0.2 kg S/m³-d) was achieved without changing the acidic condition (pH around 4.3) in a sulfur reduction bio-reactor. With the acidic sulfide-containing effluents from the bio-reactor, over 99% of arsenite (10 mg As/L) in the arsenic-contaminated water was precipitated without the formation of soluble thioarsenite by-products, even in the presence of excessive sulfide. Maintaining the acidic condition (pH around 4.3) of the sulfide-containing effluent was essential to ensure the efficient arsenite precipitation and minimize the formation of thioarsenite by-products when the arsenite to sulfide molar ratios ranged from 0.1 to 0.46. An acid-tolerant S⁰RB, Desulfurella, was found to be responsible for the efficient dissimilatory sulfur reduction under acidic conditions without changing the solution pH significantly. The microbial sulfur reduction may proceed through the direct electron transfer between the S⁰RB and sulfur particles, and also through the indirect electron transport mediated by electron carriers. The findings of this study demonstrate that the proposed sulfidogenic process driven by S⁰RB working under acidic conditions can be a promising alternative to the SRB-based process for arsenite removal from the arsenic-contaminated waters.

Facet-Inspired Core-Shell Gold Nanoislands on Metal Oxide Octadecahedral Heterostructures: High Sensing Performance toward Sulfide in Biotic Fluids

The development of structurally modified metal oxide heteroarchitectures with higher energy facets exposed has been of extensive research interests because of their unique construction and synergy effect of multifunctioning characteristics. In this study, we reported for the first time the development of a distinct type of gold nanoislands (AuNIs) on metal oxides (i.e., Cu₂O-CuO) octadecahedral (ODH) heterostructures through the galvanic exchange reaction, where Cu₂O not only acts as a stabilizer but also functions as a reductant. The electrocatalytic performance of the resultant core-shell Cu₂O-CuO@AuNI ODH-based electrochemical sensing platform has been evaluated in ultrasensitive detection of sulfide as early disease diagnostics and bacterial marker. Owing to the synergistic collaboration of enhanced surface active sites, exposed {110} crystallographic facets, mixed valances of copper that encourage redox reactions at electrode material/analyte interface, and the polarization effect provide by AuNIs decorated onto the Cu₂O surface, Cu₂O-CuO@AuNI ODH-modified electrode has demonstrated striking electrochemical sensing performance toward sulfide oxidation in terms of broad linear range, real detection limit down to 1 nM (S/N = 3), and incredible durability and reproducibility. In virtue of marvelous efficiency, the proposed electrochemical sensor based on Cu₂O-CuO@AuNI ODH has been employed in in situ sensitive detection of a ubiquitous amount of sulfide engendered by sulfate-reducing bacteria and real-time tracking of sulfide efflux from live cells as early diagnostic strategies.

Removal of sulfate and heavy metals by sulfate-reducing bacteria in an expanded granular sludge bed reactor

The objective of this study is to utilize an expanded granular sludge bed reactor for removing heavy metals and sulfate from synthetic acid-mine drainage (AMD) using sewage sludge fermentation centrate as the substrate. The reactor was bioaugmented with an enriched consortium of sulfate-reducing bacteria (SRB). The bioreactor performance was studied with different chemical oxygen demand [Formula: see text] ratios, liquid upflow velocity (V_up), hydraulic retention time (HRT) and influent pH. The highest COD, sulfate and heavy metal removal efficiencies were achieved at a [Formula: see text] ratio of 1.5, V_up of 4.0 m/h, HRT of 15 h and influent pH of 6.0 (68.2%, 92.1% and 100%, respectively). The activity of SRB greatly increases the effluent pH. Even at an influent pH of 3.0, 60.8% of sulfate, 41.3% of COD and 91.2% of heavy metals could be removed, and the effluent quality can meet the national discharge standard of China. The activity tests demonstrate that the sludge fermentation centrate is an excellent carbon source for SRB. This study shows the potential of synchronous treatment of residual sewage sludge and treatment of AMD.

A Pure Life: The Microbial Ecology of High Purity Industrial Waters

The microbial ecology of various natural environments has been an active area of research since the earlier part of the twentieth century. Remote and sometimes extreme environments such as the deep ocean and the deep terrestrial subsurface have revealed a remarkable array of microorganisms. The majority of these environments are nutrient limited, and microorganisms-principally, bacteria-have developed a number of survival strategies that enable their survival and, in some cases, replication. While planktonic microorganisms exist in oligotrophic environments, the predominant mode of survival and growth is associated with biofilms. There are a number of similarities between the physicochemistry of industrial water systems and some natural aquatic ecosystems, and these similarities extend to the microbial populations and the survival mechanisms that are employed. The "starvation-survival" mechanisms, including biofilm formation, may be associated with deleterious effects on industrial water systems. These effects include heat transfer inhibition, microbially influenced corrosion, and contamination of various products manufactured in a wide array of industries. Biological fouling of industrial water systems has significant direct and indirect (through antimicrobial chemical applications) impacts on engineered materials and on the etiology of some waterborne diseases. This review provides an overview of the microbial ecology of purified waters and discusses the impacts of biological activity on industrial systems.

Treatment impacts on temporal microbial community dynamics during phytostabilization of acid-generating mine tailings in semiarid regions

Direct revegetation, or phytostabilization, is a containment strategy for contaminant metals associated with mine tailings in semiarid regions. The weathering of sulfide ore-derived tailings frequently drives acidification that inhibits plant establishment resulting in materials prone to wind and water dispersal. The specific objective of this study was to associate pyritic mine waste acidification, characterized through pore-water chemistry analysis, with dynamic changes in microbial community diversity and phylogenetic composition, and to evaluate the influence of different treatment strategies on the control of acidification dynamics. Samples were collected from a highly instrumented one-year mesocosm study that included the following treatments: 1) unamended tailings control; 2) tailings amended with 15% compost; and 3) the 15% compost-amended tailings planted with Atriplex lentiformis. Tailings samples were collected at 0, 3, 6 and 12months and pore water chemistry was monitored as an indicator of acidification and weathering processes. Results confirmed that the acidification process for pyritic mine tailings is associated with a temporal progression of bacterial and archaeal phylotypes from pH sensitive Thiobacillus and Thiomonas to communities dominated by Leptospirillum and Ferroplasma. Pore-water chemistry indicated that weathering rates were highest when Leptospirillum was most abundant. The planted treatment was most successful in disrupting the successional evolution of the Fe/S-oxidizing community. Plant establishment stimulated growth of plant-growth-promoting heterotrophic phylotypes and controlled the proliferation of lithoautotrophic Fe/S-oxidizers. The results suggest the potential for eco-engineering a microbial inoculum to stimulate plant establishment and inhibit proliferation of the most efficient Fe/S-oxidizing phylotypes.

Hybrid soliwave technique for mitigating sulfate-reducing bacteria in controlling biocorrosion: a case study on crude oil sample

Microbiologically influenced corrosion (MIC) is among the common corrosion types for buried and deep-water pipelines that result in costly repair and pipeline failure. Sulfate-reducing bacteria (SRB) are commonly known as the culprit of MIC. The aim of this work is to investigate the performance of combination of ultrasound (US) irradiation and ultraviolet (UV) radiation (known as Hybrid soliwave technique, HyST) at pilot scale to inactivate SRB. The influence of different reaction times with respect to US irradiation and UV radiation and synergistic effect toward SRB consortium was tested and discussed. In this research, the effect of HyST treatment toward SRB extermination and corrosion studies of carbon steel coupon upon SRB activity before and after the treatment were performed using weight loss method. The carbon steel coupons immersed in SRB sample were exposed to HyST treatment at different time of exposure. Additionally, Field Emission Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy were used to investigate the corrosion morphology in verifying the end product of SRB activity and corrosion formation after treatment. Results have shown that the US irradiation treatment gives a synergistic effect when combined with UV radiation in mitigating the SRB consortium.

Anaerobic oxidation of methane coupled to thiosulfate reduction in a biotrickling filter

Microorganisms from an anaerobic methane oxidizing sediment were enriched with methane gas as the substrate in a biotrickling filter (BTF) using thiosulfate as electron acceptor for 213days. Thiosulfate disproportionation to sulfate and sulfide were the dominating sulfur conversion process in the BTF and the sulfide production rate was 0.5mmoll^-1day^-1. A specific group of sulfate reducing bacteria (SRB), belonging to the Desulforsarcina/Desulfococcus group, was enriched in the BTF. The BTF biomass showed maximum sulfate reduction rate (0.38mmoll^-1day^-1) with methane as sole electron donor, measured in the absence of thiosulfate in the BTF. Therefore, a BTF fed with thiosulfate as electron acceptor can be used to enrich SRB of the DSS group and activate the inoculum for anaerobic oxidation of methane coupled to sulfate reduction.

Assessment of the performance of SMFCs in the bioremediation of PAHs in contaminated marine sediments under different redox conditions and analysis of the associated microbial communities

The biodegradation of naphthalene, 2-methylnaphthalene and phenanthrene was evaluated in marine sediment microbial fuel cells (SMFCs) under different biodegradation conditions, including sulfate reduction as a major biodegradation pathway, employment of anode as terminal electron acceptor (TEA) under inhibited sulfate reducing bacteria activity, and combined sulfate and anode usage as electron acceptors. A significant removal of naphthalene and 2-methylnaphthalene was observed at early stages of incubation in all treatments and was attributed to their high volatility. In the case of phenanthrene, a significant removal (93.83±1.68%) was measured in the closed circuit SMFCs with the anode acting as the main TEA and under combined anode and sulfate reduction conditions (88.51±1.3%). A much lower removal (40.37±3.24%) was achieved in the open circuit SMFCs operating with sulfate reduction as a major biodegradation pathway. Analysis of the anodic bacterial community using 16S rRNA gene pyrosequencing revealed the enrichment of genera with potential exoelectrogenic capability, namely Geoalkalibacter and Desulfuromonas, on the anode of the closed circuit SMFCs under inhibited SRB activity, while they were not detected on the anode of open circuit SMFCs. These results demonstrate the role of the anode in enhancing PAHs biodegradation in contaminated marine sediments and suggest a higher system efficiency in the absence of competition between microbial redox processes (under SRB inhibition), namely due to the anode enrichment with exoelectrogenic bacteria, which is a more energetically favorable mechanism for PAHs oxidation than sulfate.

[Feasibility of 3BER-S Process for the Deep Denitrification in Synch with the Removal of PAEs from Reclaimed Water]

In order to investigate the feasibility of deep denitrification and simultaneous removing phthalate esters (PAEs) in the process of reclaimed water treatment uses three-dimensional biofilm-electrode reactor coupled with sulfur autotrophic deep denitrification technology (3BER-S), the technological characteristics and mechanisms were analyzed based on determining the static adsorption capacity of biofilm cultured active carbon fillers in 3BER-S reactor together with the operation results of dynamic denitrification and simultaneous PAEs removing. The results showed that the average adsorption rates of DBP, DEHP were 85.84% and 97.12% in the biofilm cultured active carbon fillers, the equilibrium adsorption capacities were 0.1426 mg x g(-1) and 0.162 mg(-1) and the time spans of reaching adsorption saturation were 120 min and 60 min, respectively; The existence of PAEs had no obvious effect on denitrification, the reactor effluent concentration of TN was in range of 1-2 mg x L(-1) before and after the addition of PAEs, and the average removal rate of TN reached above 94%; 3BER-S denitrification system showed significant ability in removing PAEs, leading to effluent concentrations of DBP and DEHP of no more than 6 microg x L(-1) with removal rates of above 96%; this was due to the synergistic effect of absorption, biodegradation and electrochemistry. After treatment with 3BER-S technology, DBP and DEHP in simulative municipal secondary effluent met the regulated limitation of The Reuse of Urban Recycling Water Quality Standard for Groundwater Recharge (GB/T 19772-2005).

Comparative contributions of solution geochemistry, microbial metabolism and aquatic photosynthesis to the development of high pH in ephemeral wetlands in South East Australia

The development of alkaline conditions in lakes and wetlands is common but the process of alkalinisation is not well elaborated. In this study we investigated causes of the seasonal alkalinisation of ephemeral wetlands in the South East of South Australia where pH values above 10 are frequently observed. This research combined field observations, geochemical analysis of wetland sediment and surface water, with mesocosm studies under controlled conditions. The results revealed a complex interplay between a number of different processes. A primary cause was attributed to sequestration of CO2 from the water column by plant photosynthesis, coupled with slow diffusion of CO2 from the air which led to its depletion in the water. Abundant plant growth also modified the water chemistry via uptake of nutrient elements, in particular calcium and magnesium and increased carbonate alkalinity in the water. Assessment of field results and geochemical modeling showed that low Ca/(HCO3(-) and CO3(-2)) ratios in the water, coupled with carbonate mineral (calcite, Mg substituted calcite, dolomite) precipitation and evapoconcentration, create a high alkalinity and pH (>9) baseline in many wetlands. The high baseline pH is then further increased by CO2 depletion due to photosynthesis. We could find no evidence that reduction of sulfate to sulfides by sulfur-reducing bacteria significantly contributed to the very high pH conditions.

[Application of Micro-aerobic Hydrolysis Acidification in the Pretreatment of Petrochemical Wastewater]

Micro-aerobic hydrolysis acidification technology was applied in the reconstruction of ananaerobic hydrolysis acidification tank in a north petrochemical wastewater treatment plant. After put into operation, the monitoring results showed that the average removal rate of COD was 11.7% when influent COD was 490.3-673.2 mg x L(-1), hydraulic retention time (HRT) was 24 and the dissolved oxygen (DO) was 0.2-0.35 mg x L(-1). In addition, the BOD5/COD value was increased by 12.4%, the UV254 removal rate reached 11.2%, and the VFA concentration was increased by 23.0%. The relative molecular weight distribution (MWD) results showed that the small molecule organic matter (< 1 x 10(3)) percentage was increased from 59.5% to 82.1% and the high molecular organic matter ( > 100 x 10(3)) percentage was decreased from 31.8% to 14.0% after micro-aerobic hydrolysis acidification. The aerobic biodegradation batch test showed that the degradation of petrochemical wastewater was significantly improved by the pretreatment of micro-aerobic hydrolysis acidification. The COD of influent can be degraded to 102.2 mg x L(-1) by 48h aerobic treatment while the micro-aerobic hydrolysis acidification effluent COD can be degraded to 71.5 mg x L(-1) on the same condition. The effluent sulfate concentration of micro-aerobic hydrolysis acidification tank [(930.7 ± 60.1) mg x L(-1)] was higher than that of the influent [(854.3 ± 41.5) mg x L(-1)], indicating that sulfate reducing bacteria (SRB) was inhibited. The toxic and malodorous gases generation was reduced with the improvement of environment.

[Research on removal efficiency of Cd (II)-bearing wastewater by sulfate-reducing biological filter]

At the temperature of 18.0-22.3 degrees C, biological carriers were produce from pure SRB and zeolite by the embedding immobilized method, and a sulfate-reducing biological filter filled with filter carriers was built to treat cadmium-containing wastewater. Experimental research on removal efficiency of Cd2+, COD and SO4(2-) in wastewater by the biological filter was carried out after SRB domestication. Results show that cadmium can be removed satisfactorily from wastewater using SRB by the biological filter filled with sulfate-reducing bacteria. When the filtration rate was 0.4 m x h(-1) and the cadmium concentration in wastewater was not more than 15 mg x L(-1), the processing efficiency was the best. In the formal running period, the removal rates of Cd2+, COD and SO4(2-) by the biological filter were more than 99%, 75% and 50%. The effluent Cd2+ concentration was less than 0.1 mg x L(-1), which could meet the cadmium emission requirements in the wastewater quality standards for discharge to municipal sewers (CJ 343-2010). The removal of Cd2+, COD and SO4(2-) by biological filter mainly occurs in the top 60 cm of the filter bed during stable operation. When the filtration rate was less than 0.6 m x h(-1), Cd(2+) can be removed by the biological filter with high efficiency and stability.

Pseudomorphs of barite and biogenic ZnS after phyto-crystals of calcium oxalate (whewellite) in the peat layer of a poor fen

Pseudomorphs of barite (BaSO4) and Cd-rich ZnS after whewellite (CaC2O4·H2O) occur within remnants of Scots pine bark tissues in the peat layer of a poor fen located near a zinc smelter in south Poland. A two-step formation of the pseudomorphs is postulated based on SEM observations: (1) complete dissolution of whewellite, possibly caused by oxalotrophic bacteria, and (2) subsequent bacterially induced precipitation of barite and spheroidal aggregates of ZnS together with galena (PbS) in voids left by the dissolved whewellite crystals. Local increase in pH due to microbial degradation of whewellite, elevated concentrations of Zn(II) and Ba(II) in pore water due to the decomposition of atmospheric particles of sphalerite and barite in the acidic (pH 3.5-3.8) environment, oxidation of S species during drying and rewetting of the peat layer, and subsequent partial reduction of sulfate anions by sulfur-reducing bacteria were all factors likely involved in the crystallization of ZnS and barite in the microenvironment of the post-whewellite voids.

Effect of an essential oil-containing mouth rinse on VSC-producing bacteria on the tongue

The objective of the present study was to investigate the inhibitory effect of a commercially available essential oil-containing mouth rinse 12 hours after a single rinse and two weeks of twice daily rinsing, on volatile sulphur compounds (VSC) producing bacteria on the tongue. The study was a randomized, double-blind, controlled crossover design. Thirty-six healthy subjects, aged 20-48 years, volunteered to participate in the study. Subjects were randomly assigned to rinse twice daily with either an essential oil-containing mouth rinse (Cool Mint Listerine Antiseptic) or a negative control rinse. Bacteria samples were taken from the dorsum of the tongue at baseline, after the first rinse and two weeks later. They were plated on OOPS medium to enumerate the VSC-producing bacteria. Intergroup comparisons of log10 transformed colony-forming units of the samples were made using analysis of covariance. Each comparison was performed at a 5% significance level. The mean VSC-producing bacteria in subjects using the essential oil mouth rinse were significantly lower than those using the control rinse twice daily. In healthy subjects, rinsing with an essential oil-containing mouth rinse can have a significant effect on VSC-producing bacteria on the tongue and may be useful for controlling intrinsic oral malodor over prolonged periods.

[A microbiological study of an underground gas storage in the process of gas injection]

The liquid phase of different units of an underground gas storage (UGS) in the period of gas injection was studied with respect to its hydrochemical composition and characterized microbiologically. The presence of viable aerobic and anaerobic bacteria was revealed in the UGS stratal and associated waters. An important source of microorganisms and biogenic elements in the ecosystem studied is water and various technogenic admixtures contained in trace amounts in the gas entering from the gas main in the period of gas injection into the storage. Owing to this fact, the bacterial functional diversity, number, and activity are maximal in the system of gas treatment and purification and considerably lower in the observation well zone. At the terminal stages, the anaerobic transformation of organic matter in the UGS aqueous media occurs via sulfate reduction and methanogenesis; exceptionally high rates of these processes (up to 4.9 x 10(5) ng S(2-)l(-1) day(-1) and 2.8 x 10(6) nl CH4 l(-1) day(-1), respectively) were recorded for above-ground technological equipment.

Desulfosporosinus lacus sp. nov., a sulfate-reducing bacterium isolated from pristine freshwater lake sediments

A novel sulfate-reducing bacterium was isolated from pristine sediments of Lake Stechlin, Germany. This strain, STP12T, was found to contain predominantlyc-type cytochromes and to reduce sulfate, sulfite and thiosulfate using lactate as an electron donor. Although STP12Tcould not utilize elemental sulfur as an electron acceptor, it could support growth by dissimilatory Fe(III) reduction. In a comparison of 16S rRNA gene sequences, STP12Twas 96.7 % similar toDesulfosporosinus auripigmentiDSM 13351T, 96.5 % similar toDesulfosporosinus meridieiDSM 13257Tand 96.4 % similar toDesulfosporosinus orientisDSM 765T. DNA–DNA hybridization experiments revealed that strain STP12Tshows only 32 % reassociation with the type strain of the type species of the genus,D. orientisDSM 765T. These data, considered in conjunction with strain-specific differences in heavy metal tolerance, cell-wall chemotaxonomy and riboprint patterns, support recognition of strain STP12T(=DSM 15449T=JCM 12239T) as the type strain of a distinct and novel species within the genusDesulfosporosinus,Desulfosporosinus lacussp. nov.

Effect of reactive media composition and co-contaminants on sulfur-based autotrophic denitrification

As a part of a study developing a biological reactive barrier system to treat nitrate-contaminated groundwater, the effects of reactive media composition and co-contaminants on sulfur-oxidizing autotrophic denitrification were investigated. The size of sulfur granules affected the denitrification rates; kinetic constants of 2.883, 2.949, and 0.677 mg-N(1/2)/L(1/2)/day were obtained when the granule sizes were below 2 mm, between 2 and 5 mm, and over 5 mm, respectively. When the volume ratios of sulfur to limestone were 1:1, 2:1, 3:1, and 4:1, kinetic constants of 5.490, 3.903, 4.072, and 2.984 mg-N(1/2)/L(1/2)/day were obtained, respectively. The presence of TCE up to 20 mg/L didn't significantly affect nitrate removal efficiency. At the TCE concentration of 80 mg/L, however, nitrate removal was markedly inhibited. Also, Zn and Cu inhibited the denitrification activity at more than 0.5 mg/L of concentration whereas Cr (VI) did not significantly affect the nitrate removal efficiency at all levels tested.

Microbial reductive dechlorination of weathered and exogenous co-planar polychlorinated biphenyls (PCBs) in an anaerobic sediment of Venice Lagoon

The occurrence of reductive dechlorination processes towards pre-existing PCBs and five exogenous coplanar PCBs were investigated in a contaminated sediment of Porto Marghera (Venice Lagoon, Italy) suspended, under strictly anaerobic conditions, in water collected from the same site. PCB dechlorination started after five months of incubation, when sulfate initially occurring in the microcosms was completely depleted and methanogenesis was in progress. It was ascribed to sulfate-reducing bacteria. Several pre-existing hexa-, penta- and tetra-chlorinated biphenyls were slowly bioconverted into tri- and di-, ortho-substituted PCBs from the 5th to the 16th month of experiment. Spiked coplanar PCBs, i.e., 3,3',4,4'-tetrachlorobiphenyl, 3,3',4,4',5- and 2,3',4,4',5-pentachlorobiphenyls, 3,3',4,4',5,5'- and 2,3,3',4,4',5-hexachlorobiphenyls, were extensively transformed (by about 90%) into lower chlorinated congeners, such as 3,3',5,5'-/2,3',4,4'-tetrachlorobiphenyl, 3,3',5-, 2,4,4'-, 2,3',4- and 2,3',5-trichlorobiphenyl, 3,4-/3,4'- and 3,3'-dichlorobiphenyl and 2-chlorobiphenyl. The reductive dechlorination of spiked PCBs did not influence significantly the biotransformation rate and extent of pre-existing PCBs.

Changes in bacterial community structure correlate with initial operating conditions of a field-scale denitrifying fluidized bed reactor

High levels of nitrate are present in groundwater migrating from the former waste disposal ponds at the Y-12 National Security Complex in Oak Ridge, TN. A field-scale denitrifying fluidized bed reactor (FBR) was designed, constructed, and operated with ethanol as an electron donor for the removal of nitrate. After inoculation, biofilms developed on the granular activated carbon particles. Changes in the bacterial community of the FBR were evaluated with clone libraries (n = 500 partial sequences) of the small-subunit rRNA gene for samples taken over a 4-month start-up period. Early phases of start-up operation were characterized by a period of selection, followed by low diversity and predominance by Azoarcus-like sequences. Possible explanations were high pH and nutrient limitations. After amelioration of these conditions, diversification increased rapidly, with the appearance of Dechloromonas, Pseudomonas, and Hydrogenophaga sequences. Changes in NO3, SO4, and pH also likely contributed to shifts in community composition. The detection of sulfate-reducing-bacteria-like sequences closely related to Desulfovibrio and Desulfuromonas in the FBR have important implications for downstream applications at the field site.

Production of antimicrobial substances by Bacillus subtilis LFE-1, B. firmus H2O-1 and B. licheniformis T6-5 isolated from an oil reservoir in Brazil

AIMS

Forty Bacillus strains isolated from a Brazilian oil reservoir were tested against each other to select strains producing antimicrobial substances (AMS). Three strains, Bacillus subtilis (LFE-1), Bacillus firmus (H2O-1) and Bacillus licheniformis (T6-5), were selected due to their ability to inhibit more than 65% of the Bacillus strains tested. These three strains were also investigated for their capability to inhibit sulphate-reducing bacteria (SRB). Furthermore, physiological and biochemical characteristics of the antimicrobial compounds produced by the selected strains were determined.

METHODS AND RESULTS

Among the forty strains tested, 36 (90%) strains were able to inhibit at least one Bacillus strain used as indicator in plate assays and three of them (LFE-1, T6-5 and H2O-1) were able to inhibit 65, 70 and 97.5% of the 40 strains studied here respectively. Clear zones of inhibition were observed when H2O-1 was tested against SRB-containing consortium T6-lab and Desulfovibrio alaskensis strain NCIMB 13491, while strain T6-5 was able to inhibit only the D. alaskensis strain. The three substances showed to be insensitive to different enzymes and chemicals, were heat stable and the substances produced by strains T6-5 and H2O-1 were active over a wide pH range.

CONCLUSIONS

Three different AMS produced by Bacillus strains from an oil reservoir, two of them with activity against SRB, are presented here.

SIGNIFICANCE AND IMPACT OF THE STUDY

The preliminary characterization of these AMS points to their potential use as biocides in the petroleum industry for controlling problems associated with SRB.

Oxidation of fugitive methane in ground water linked to bacterial sulfate reduction

When fugitive methane migrates upward along boreholes of oil and gas wells, it may migrate into shallow ground water or pass through overlying soil to the atmosphere. Prior to this study, there was little information on the fate of fugitive methane that migrates into ground water. In a field study near Lloydminster, Alberta, Canada, we found hydrogeochemical evidence that fugitive methane from an oil well migrated into a shallow aquifer but has been attenuated by dissimilatory bacterial sulfate reduction at low temperature ( approximately 5 degrees C) under anaerobic conditions. Evidence includes spatial and temporal trends in concentrations of methane and sulfate in ground water and associated trends in concentrations of bicarbonate and sulfide. Within 10 m of the oil well, sulfate concentrations were low, and sulfate was enriched in both 34S and 18O. Sulfate concentrations had a strong positive correlation with delta13C values of bicarbonate, and sulfide was depleted in 34S compared to sulfate. These data indicate that bacterial sulfate reduction occurred near the production well. Near the oil well, elevated concentrations of bicarbonate were observed, and the bicarbonate was depleted in 13C. Modeling indicates that the main source of this excess 13C-depleted bicarbonate is oxidized methane. In concert with the sulfate concentration and isotope data, these results support an interpretation that in situ bacterial oxidation of methane has occurred, linked to bacterial sulfate reduction. Bacterial sulfate reduction may play a major role in bioattenuation of fugitive natural gas in ground water in western Canada.

The use of micro-algal biomass as a carbon source for biological sulphate reducing systems

An upflow anaerobic digestor was fed dried algal biomass as a carbon source to establish the feasibility of using micro-algal biomass as the sole carbon source for biological sulphate reduction. The effect of the COD:SO4 ratio on substrate consumption and sulphate removal efficiencies were assessed by varying the organic carbon content of the media. Similar COD removal efficiencies were obtained irrespective of the influent COD:SO4 ratios, which were 8.1, 11.2 and 15.0. However, the rates of COD removal did differ with influent COD:SO4 ratios. The percentage sulphate removed decreased as the ratio of COD:SO4 increased. Not all of the COD was used for sulphate reduction, with only 31% being accounted for.

Tannery effluent as a carbon source for biological sulphate reduction

Tannery effluent was assessed as a carbon source for biological sulphate reduction in a pilot-scale upflow anaerobic sludge blanket (UASB), stirred tank reactor (STR) and trench reactor (TR). Sulphate removals of between 60-80% were obtained in all three reactors at total sulphate feed levels of up to 1800 mg l(-1). Sulphate removal in the TR (400-500 mg SO4 l(-1) day(-1)) and UASB (up to 600 mg SO4 l(-1) day(-1)) were higher than those obtained in the STR (250 mg SO4 l(1) day(-1)). A change in operation mode from a UASB to a STR had a large impact on chemical oxygen demand (COD) removal efficiencies. COD removal rates decreased by 25% from 600-700 mg COD l(-1) day(-1) to 200-600 mg COD l(-1) day(-1). The TR had an average COD removal rate of 500 mg COD l(-1) day(-1). Large quantities of sulphide were produced in the reactors (up to 1500 mg l(-1)). However due to the elevated pH in the reactor, only a small amount was in the form of H2S and thus the odour problem normally associated with biological sulphate reduction was not present.

Methanogen population in a marine biofilm corrosive to mild steel

This study was conducted to analyze the methanogen population in a corrosive marine biofilm based on 16S rDNA analysis, using a PCR-cloning-sequencing approach. There were 80 methanogen clones developed from the PCR-amplified DNA extracted from the biofilm on the mild steel surface. All clones were categorized into one of five operational taxonomy units (OTUs). Two OTUs (comprising 57 clones) were affiliated with the acetotrophic Methanosaeta genus; the remaining three OTUs (23 clones) were affiliated with the hydrogenotrophic genera of Methanogenium, Methanoplanus and Methanocalculus. The hydrogenotrophic methanogens could directly cause metal corrosion through cathodic depolarization, whereas the acetotrophic methanogens grew syntrophically with corrosion-causing sulfate-reducing bacteria, as observed by fluorescent in situ hybridization, and thus contribute indirectly to metal corrosion.

pH, dissolved oxygen, and adsorption effects on metal removal in anaerobic bioreactors

Anaerobic bioreactors were used to test the effect of the pH of influent on the removal efficiency of heavy metals from acid-rock drainage. Two studies used a near-neutral-pH, metal-laden influent to examine the heavy metal removal efficiency and hydraulic residence time requirements of the reactors. Another study used the more typical low-pH mine drainage influent. Experiments also were done to (i) test the effects of oxygen content of feed water on metal removal and (ii) the adsorptive capacity of the reactor organic substrate. Analysis of the results indicates that bacterial sulfate reduction may be a zero-order kinetic reaction relative to sulfate concentrations used in the experiments, and may be the factor that controls the metal mass removal efficiency in the anaerobic treatment systems. The sorptive capacities of the organic substrate used in the experiments had not been exhausted during the experiments as indicated by the loading rates of removal of metals exceeding the mass production rates of sulfide. Microbial sulfate reduction was less in the reactors receiving low-pH influent during experiments with short residence times. Sulfate-reducing bacteria may have been inhibited by high flows of low-pH water. Dissolved oxygen content of the feed waters had little effect on sulfate reduction and metal removal capacity.

[Leptospirillum-like bacteria and their role in pyrite oxidation]

Two strains of Leptospirillum-like bacteria isolated from dumps of Alaverdi and Akhtala sulfide ore deposits in Armenia were studied. The optimum and maximum temperatures for the growth of both strains were 37 and 40 degrees C, respectively. The pH optimum was 2.0-2.3. Bacterial growth and ferrous iron oxidation were inhibited by yeast extract. The pyrite-leaching activity of the Leptospirillum-like bacteria under mesophilic conditions was close to that of Acidithiobacillus ferroxidans and exceeded by 2.0-2.7 times the activity of these moderately thermophilic bacteria at 37 degrees C. The leaching of pyrite by Leptospirillum-like bacteria increased in the presence of sulfur-oxidizing bacteria, particularly, in their association with a thermotolerant sulfur-oxidizing bacterium.

Sulfur and carbon cycling in a flue gas desulfurization sludge disposal site

Products of a power plant flue gas desulfurization scrubber are discharged into a pond as sludge consisting of calcite (initial delta13C 3.2-3.8 per thousand), gypsum (initial delta34S 7.6-8.6 per thousand), and aqueous solution. Reducing conditions exist below a boundary that appears to move vertically as a function of changes in pond water level. Under reducing conditions, bacteria partially reduce aqueous sulfate to low-delta34S sulfide, consuming organic carbon and generating low-delta13C bicarbonate. Under oxidizing conditions, sulfide is converted to sulfate, leading to calcite dissolution, gypsum precipitation, and isotopic re-equilibration of remaining calcite with dissolved bicarbonate near the pond surface. The gypsum has delta34S near 6 per thousand, and calcite has delta13C as low as -1.7 per thousand; the changes from initial values correspond to predictions based on isotopic balance and reaction stoichiometry. The pond largely contains the products of bacterial reduction. After the pond is abandoned, these products may adversely affect attempts to revegetate the site. Future bacterial reduction may be best controlled by dewatering and limiting the supply of organic matter in percolating surface water.

Nitrate removal by simultaneous sulfur utilizing autotrophic and heterotrophic denitrification under different organics and alkalinity conditions: batch experiments

The effect of various organic compounds were tested using lab-scale batch reactors. At sufficient alkalinity, the initial nitrate nitrogen concentration of 100 mg/L was completely reduced in all batch reactors. Sulfate production decreased by the addition of organics. The concentration range of organics used in this experiment did not inhibit autotrophic denitrification except for propionate. Propionate inhibited autotrophic denitrification a little, indicated by a lower sulfate production rate. Biomass in suspension increased with higher initial organic concentrations, showing higher DOC consumption. As the concentration of organics increased, alkalinity increased accordingly. Under the conditions of low alkalinity, in the case of a control reactor without organics, only about 30% of the initial nitrate was reduced. With half the theoretically required dosage of methanol, the denitrification rates increased slightly. When ethanol, acetate, and propionate were used, denitrification went to completion. When excess organics was added, however, sulfate production was significantly decreased. Interestingly, even when small amounts of organics were added, autotrophic denitrification was promoted as indicated by the sulfate production.

Co-digestion of primary sewage sludge and industrial wastewater under anaerobic sulphate reducing conditions: enzymatic profiles in a recycling sludge bed reactor

The first stage in the degradation and recycling of primary sewage sludge and particulate organic matter is the solubilisation and enhanced hydrolysis of complex polymeric organic carbon structures associated with the anaerobic sulphidogenic environment. Solubilization of complex carbon substrates provides the primary reaction in the BioSURE Process, and is effected in the recycling sludge bed reactor (RSBR). During the process of anaerobic digestion, macromolecules are broken down into simpler low molecular weight compounds in the presence of extracellular enzymes. Though hydrolysis of the complex carbon sources was enhanced under biosulphidogenic conditions, no studies have examined the role of enzymes and the enzymatic profiles in the RSBR. To investigate the overall enzymology in the RSBR variations in COD, pH, sulphate, sulphite and sulphide concentrations, carbohydrates, protein and activities of glucosidases, proteases and lipases were studied over 50 days in the reactor at three different depths: 0-16 cm; 16-32 cm; 32-50 cm. While the pH profile remained fairly constant between 6.9 and 7.3 the sulphate and sulphide levels, as expected, changed dramatically as sulphate reduction took place. Proteases, lipases and glucosidases all showed enhanced activity with depth in the bioreactor. It is suggested that the increased sulphide concentration generated during the sulphate reduction process stimulates the enzymes, leading to enhanced solubilisation of primary sewage sludge.

Methanogenic potential of tailings samples from oil sands extraction plants

Approximately 20% of Canada's oil supply now comes from the extraction of bitumen from the oil sands deposits in northeastern Alberta. The oil sands are strip-mined, and the bitumen is typically separated from sand and clays by an alkaline hot water extraction process. The rapidly expanding oil sands industry has millions of cubic metres of tailings for disposal and large areas of land to reclaim. There are estimates that the consolidation of the mature fine tails (MFT) in the settling ponds will take about 150 years. Some of the settling ponds are now evolving microbially produced methane, a greenhouse gas. To hasten consolidation, gypsum (CaSO4 x 2H2O) is added to MFT, yielding materials called consolidated or composite tailings (CT). Sulfate from the gypsum has the potential to stimulate sulfate-reducing bacteria (SRB) to out-compete methanogens, thereby stopping methanogenesis. This investigation examined three MFT and four CT samples from three oil sands extractions companies. Each was found to contain methanogens and SRB. Serum bottle microcosm studies showed sulfate in the CT samples stopped methane production. However, if the microcosms were amended with readily utilizable electron donors, the sulfate was consumed, and when it reached approximately 20 mg/L, methane production began. Some unamended microcosms were incubated for 372 days, with no methane production detected. This work showed that each MFT and CT sample has the potential to become methanogenic, but in the absence of exogenous electron donors, the added sulfate can inhibit methanogenesis for a long time.

Biotransformation of explosive-grade nitrocellulose under denitrifying and sulfidogenic conditions

Waste nitrocellulose (NC) is regulated as a hazardous material. The objective of this study was to determine if NC exposed to denitrifying and sulfidogenic conditions would undergo sufficient removal of the nitro groups to yield a material that is no longer explosive. Enrichment cultures were established with methanol as the electron donor for nitrate-reducing conditions and lactate for sulfate-reducing conditions. NC was added to the cultures at 10 g/l. A statistically significant decrease in the nitrogen (N) content of NC occurred in both enrichment cultures, from approximately 13.1-13.2% in virgin NC to 12.2-12.4%. This was accompanied by an increase in nitrogen gas formation. The presence of a primary substrate (methanol and lactate) was necessary to affect this change; NC itself did not serve as an electron donor. In cultures that were carrying out denitrification but were then depleted of nitrate, with methanol still present, a slightly greater removal of nitro groups from NC occurred along with additional formation of nitrogen gas. NC did not have an inhibitory affect on the denitrification process but it did significantly slow the rate of lactate consumption and sulfate reduction. Fourier Transform Infrared Spectroscopy (FTIR) results indicated that NC exposed to denitrifying conditions was enriched in hydroxyl groups, consistent with removal of some of the nitro groups by hydrolysis of the nitrate esters. NC exposed to nitrate- and sulfate-reducing conditions and virgin NC were also compared based on their explosive properties using a small-scale burning test. The biologically treated NC exhibited somewhat less reactivity, but was still rated as explosive. The decrease in%N, increase in N2, and FTIR results demonstrated that NC does undergo biotransformation in the presence of nitrate- and sulfate-reducing enrichment cultures, but the extent of denitration does not appear to be adequate to yield a nonhazardous product.

Genuine halitosis, pseudo-halitosis, and halitophobia: classification, diagnosis, and treatment

Although tongue brushing and appropriate mouthrinses are both important and basic treatment measures for halitosis, other dental treatments are sometimes required. The treatment of genuine halitosis caused by oral conditions is not complex. In addition to genuine halitosis patients, psychosomatic halitosis patients also visit dental practitioners. Although psychosomatic halitosis is out of the treatment realm of dental practitioners, patients with this condition will still seek help from a dental practitioner. They often only receive treatment for genuine halitosis without referral to a psychological specialist. If these psychosomatic halitosis patients are incorrectly managed, the psychological condition might become worse than before the visit. To avoid the mismanagement of halitosis patients, classifications of halitosis patients have been established. Genuine halitosis was subclassified as physiologic halitosis and pathologic halitosis. Pathologic halitosis was further categorized to oral pathologic halitosis and extraoral pathologic halitosis. Both pseudo-halitosis and halitophobia patients complain of the existence of halitosis, which is not offensive. Pseudo-halitosis cannot be treated by dental practitioners, and halitophobia patients must be referred to psychological specialists. Clinicians need to examine the psychological condition of halitosis patients at the initial patient visit. A questionnaire prepared for the clinic at the University of British Columbia was found to be advantageous for this purpose.

Light absorption by phototrophic bacteria: effects of scattering, cell concentration and size of the culture vessel

This article analyzes how absorption of light by suspensions of phototrophic bacteria is modulated by changes in the biomass of the culture, the size of the culture vessel and by the presence of refractile structures within the cells. Increases in biomass and culture size result in higher rates of light absorption but in the decrease of the amount of energy available per cell. The presence of refractile structures has different consequences depending on the biomass concentration. In dense cultures, the accumulation of refractile structures increases the reflection of light, and also reduces specific light absorption. In diluted cultures, however, the effect is the opposite, and refractile structures seem to increase light absorption.

Operation of bad breath clinics

The diagnosis and management of bad breath can be easily incorporated in routine dental care by attending dentists. This article outlines the information necessary to establish a differential diagnosis of oral malodor. This includes evaluation of medical, dental, and halitosis history. It also includes the examination of extraoral and intraoral tissues and a thorough periodontal examination. The presence of bad breath is established with organoleptic and hydrogen sulfide-monitor (Halimeter) measurements. The treatment of malodor resulting from oral overgrowth of anaerobic organisms in the oral cavity consists of mechanical and chemical reduction of the microbial flora by methods that are supported by scientific evidence.

Mechanical effects and volatile sulfur compound-reducing effects of chewing gums: comparison between test and base gums and a control group

OBJECTIVE

Chewing gum may act as a masking or a therapeutic agent against the different chemical compounds that are responsible for oral malodor. An open-label exploratory study investigated the effect of mastication and aromatic components of chewing gum on reducing oral volatile sulfur compounds.

METHOD AND MATERIALS

Twelve dental students (5 males and 7 females) acted as their own controls. Toothbrushing stopped 12 hours before observations. Measurements included organoleptic and volatile sulfur compound scores and the pH of the anterior and posterior zones of the dorsal tongue. Measurements were made at 9 AM and 12 PM on 1 day for 3 successive weeks; week 1, no gum (control); week 2, test gum; week 3, unsweetened gum base. This open-label study was then completed by an observer-blind study, according to the same schedule; the recorded measurement was the plaque index.

RESULTS

The pH, volatile sulfur compounds, and organoleptic scores were similar for all groups. The pH was more basic in the posterior part than in the anterior zone of the dorsal tongue, irrespective of time and presence or absence of chewing gum. In addition, the volatile sulfur compound score rose transiently immediately after the test gum, and the organoleptic score fell in the first hour only after the test gum. The two chewing gum groups seemed to have a greater reduction in plaque index than did the control (no gum) group.

CONCLUSION

Chewing gum may have a valuable mechanical role in cleaning dental surfaces, and the test gum may temporarily control bad breath. After 3 hours, similar volatile sulfur compound scores were observed for subjects who chewed either test or unsweetened gum base and control subjects.

Microbial hexachlorobenzene dechlorination under three reducing conditions

The potential dechlorination of hexachlorobenzene (HCB) in medium by 1,2,3-trichlorobenzene (TCB)-adapted mixed culture under three reducing conditions was investigated. It was found that strongest to weakest HCB dechlorination occurred in the order of methanogenic conditions > sulfate-reducing conditions > denitrifying conditions. Under denitrifying conditions, no dechlorination was observed during the first 20 days of incubation. Biotransformation occurred in this order: HCB-->pentachlorobenzene (PCB)-->1,2,3,5-tetrachlorobenzene (TeCB)-->1,3,5-TCB + 1,2,4-TCB-->1,3-dichlorobenzene (DCB), HCB dechlorination was delayed following treatment with ferric chloride and manganese dioxide, but enhanced by the addition of lactate and pyruvate under methanogenic or sulfate-reducing conditions, the addition of acetate had no significant effect on HCB dechlorination under any of the three reducing conditions. Sequential dechlorination was observed at concentrations of 2-50 mg/L, but at a significantly slower rate at the highest concentrations.

Domain structure of the prokaryotic selenocysteine-specific elongation factor SelB

Incorporation of the non-canonical amino acid selenocysteine into proteins requires the activity of the elongation factor SelB which substitutes for the function of EF-Tu in contrast to EF-Tu, SelB binds selenocystylated tRNASec and an mRNA secondary structure adjacent to the UGA selenocysteine codon. To gain information on the domain structure of this specialized translation factor, the selB genes from two bacteria unrelated to Escherichia coli (Clostridium thermoaceticum and Desulfomicrobium baculatum) were cloned and sequenced. The derived amino acid residue sequences were compared to those of SelB from E. coli and Haemophilus influenzae and to EF-Tu sequences. The alignment revealed that SelB contains all three domains characterized for EF-Tu. A fourth, C-terminally located domain shows only limited sequence conservation within the four SelB proteins. To elucidate the function of this C-terminal part a structure-function analysis of SelB from E. coli was performed. It showed that a C-terminal 17 kDa subdomain of the translation factor, when expressed separately, specifically binds the mRNA secondary structure. The recognition motif itself could be reduced to a 17 nucleotide minihelix without loss of binding affinity and specificity. A truncated SelB lacking the mRNA binding domain was still able to interact with selenocysteyl-tRNASec. Expression of the mRNA binding domain alone suppressed selenocysteine insertion in vivo by competing with SelB for its binding site at the mRNA. The results indicate that SelB can be considered as an EF-Tu homolog hooked to the mRNA via its C-terminal domain.

Biological degradation and composition of inedible sweetpotato biomass

Many challenges are presented by biological degradation in a bioregenerative Controlled Ecological Life Support System (CELSS) as envisioned by the U.S. National Aeronautics and Space Administration (NASA). In the studies conducted with biodegradative microorganism indigenous to sweetpotato fields, it was determined that a particle size of 75 microns and incubation temperature of 30 degrees C were optimal for degradation. The composition of the inedible biomass and characterization of plant nutrient solution indicated the presence of potential energy sources to drive microbial transformations of plant waste. Selected indigenous soil isolates with ligno-cellulolytic or sulfate-reducing ability were utilized in biological studies and demonstrated diversity in ability to reduce sulfate in solution and to utilize alternative carbon sources: a lignin analog--4-hydroxy, 3-methoxy cinnamic acid, cellulose, arabinose, glucose, sucrose, mannitol, galactose, ascorbic acid.

Terminal Proterozoic reorganization of biogeochemical cycles

The Proterozoic aeon (2,500-540 million years ago) saw episodic increases in atmospheric oxygen content, the evolution of multicellular life and, at its close, an enormous radiation of animal diversity. These profound biological and environmental changes must have been linked, but the underlying mechanisms have been obscure. Here we show that hydrocarbons extracted from Proterozoic sediments in several locations worldwide are derived mainly from bacteria or other heterotrophs rather than from photosynthetic organisms. Biodegradation of algal products in sedimenting matter was therefore unusually complete, indicating that organic material was extensively reworked as it sank slowly through the water column. We propose that a significant proportion of this reworking will have been mediated by sulphate-reducing bacteria, forming sulphide. The production of sulphide and consumption of oxygen near the ocean surface will have inhibited transport of O2 to the deep ocean. We find that preservation of algal-lipid skeletons improves at the beginning of the Cambrian, reflecting the increase in transport by rapidly sinking faecal pellets. We suggest that this rapid removal of organic matter will have increased oxygenation of surface waters, leading to a descent of the O2-sulphide interface to the sea floor and to marked changes in the marine environment, ultimately contributing to the Cambrian radiation.

Carbon isotope fractionation by thermophilic phototrophic sulfur bacteria: evidence for autotrophic growth in natural populations

Purple phototrophic bacteria of the genus Chromatium can grow as either photoautotrophs or photoheterotrophs. To determine the growth mode of the thermophilic Chromatium species, Chromatium tepidum, under in situ conditions, we have examined the carbon isotope fractionation patterns in laboratory cultures of this organism and in mats of C. tepidum which develop in sulfide thermal springs in Yellowstone National Park. Isotopic analysis (13C/12C) of total carbon, carotenoid pigments, and bacteriochlorophyll from photoautotrophically grown cultures of C. tepidum yielded 13C fractionation factors near -20%. Cells of C. tepidum grown on excess acetate, wherein synthesis of the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase ribulose bisphosphate carboxylase) was greatly repressed, were isotopically heavier, fractionation factors of ca. -7% being observed. Fractionation factors determined by isotopic analyses of cells and pigment fractions of natural populations of C. tepidum growing in three different sulfide thermal springs in Yellowstone National Park were approximately -20%, indicating that this purple sulfur bacterium grows as a photoautotroph in nature.