Biofilm formation by sulphate-reducing bacteria on different metals and their prospective role in titanium corrosion

This study describes the biofilm formation by sulphate-reducing bacteria (SRB) on different materials, which has implications for the biomedical, pharmaceutical, food and chemical process industries. SRB was chosen as a model organism being an anaerobic bacterium. Biofilm formation on different materials and corrosion of titanium by SRB were monitored with time using confocal laser scanning microscopy and fluorescent FISH probes were used to authenticate the SRB strain. The thickness of the mono-culture SRB biofilm has ranged from 4 to 24 µm during thed 12-84 hr; however, the maximum biofilm thickness (24 µm) was recorded after 60 hr of growth. Planktonic growth of the SRB strain showed a log phase up to 48 hr and the sulphide production ranged from 2 to 14 mg l-1. For a comparative account, the SRB biofilm formation on copper was chosen as a positive control. Finally, the putative role of extracellular electron transfer by SRB in the biocorrosion process and the plausible mechanism of pitting corrosion of titanium is described in detail.

Microbiologically influenced corrosion on naval carbon steel inside the hull of tugboats: a case study of prevention and control

Microbiologically influenced corrosion (MIC) has a significant cost to many industries, including naval engineering. In this case-of-study, three tugboats developed pitting corrosion in the carbon steel of the inner hulls. Grade A naval steel was used for the hull sheets but the inner side (corroded) showed only two protective layers of paint. The maintenance employed seawater, which ended up in the bilge and made MIC possible. Bilge's waters were submitted to physicochemical, biological and molecular tests. DNA analyses confirmed the presence of Pseudomonas spp. and Desulfovibrio spp. in water samples and, consequently, a MIC mechanism was proposed to explain the corrosion process. In addition, a biocide treatment was evaluated and a new maintenance protocol was recommended. This work highlights the importance of the engineering design to prevent MIC in marine transports and provides some guidelines to treat it.

Effects of Inorganic Metabolites of Sulphate-Reducing Bacteria on the Corrosion of AZ31B and AZ63B Magnesium Alloy in 3.5 wt.% NaCl Solution

This study seeks prevent and alleviate the failure of magnesium alloy anodes in pipelines, which we suspect is a problem related to SRB. The electrochemical corrosion behaviour of two kinds of magnesium alloys, AZ31B and AZ63B, in 3.5 wt.% NaCl solution with sulphide or phosphide—the two main inorganic metabolites of sulphate-reducing bacteria—were studied by electrochemical tests combined with other characterisation methods such as scanning electron microscopy and X-ray diffraction. The results show that the corrosion film formed by inorganic metabolites of SRB’s initial stage of corrosion (1–3 d) can lead to the corrosion of magnesium alloys. However, the loose and porous corrosion product film cannot protect the substrate effectively. The inorganic metabolites in the solution can accelerate the corrosion of the surface of magnesium alloy after the corrosion products have fallen off. This study provides a theoretical basis for alleviating the premature failure of magnesium alloy anodes and for corrosion protection in the future.

Desulfomarina profundi gen. nov., sp. nov., a novel mesophilic, hydrogen-oxidizing, sulphate-reducing chemolithoautotroph isolated from a deep-sea hydrothermal vent chimney

A novel mesophilic, strictly anaerobic, chemolithoautotrophic sulphate-reducing bacterium, designated strain KT2^T, was isolated from a deep-sea hydrothermal vent chimney at the Suiyo Seamount in the Izu-Bonin Arc. Strain KT2^T grew at 25-40 °C (optimum 35 °C) and pH 5.5-7.0 (optimum 6.6) in the presence of 25-45 g l^-1 NaCl (optimum 30 g l^-1). Growth occurred with molecular hydrogen as the electron donor and sulphate, thiosulphate, and sulphite as the electron acceptors. The isolate utilized CO₂ as the sole carbon source for chemolithoautotrophic growth on H₂. Glycerol, succinate, fumarate, malate, glutamate, or casamino acids could serve as an alternative electron donor in the presence of CO₂. Malate, citrate, glutamate, and casamino acids were used as fermentative substrates for weak growth. The G+C content of genomic DNA was 46.1 %. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain KT2^T is a member of the family Desulfobulbaceae, showing a sequence similarity of 94.3 % with Desulforhopalus singaporensis. Phylogenomic analysis based on concatenated 156 single-copy marker genes confirmed the same topology as the 16S rRNA gene phylogeny. The ANI and AAI values between strain KT2^T and related genera of the family Desulfobulbaceae were 65.6-68.6 % and 53.1-62.9 %. Based on the genomic, molecular, and physiological characteristics, strain KT2^T represents a novel genus and species within the family Desulfobulbaceae, for which the name Desulfomarina profundi gen. nov., sp. nov. is proposed, with KT2^T (=JCM 34118^T = DSM 111364^T) as the type strain.

Low fraction of methane in landfill gas emissions in an industrial waste landfill containing incineration ash and gypsum board waste under anaerobic conditions

The behaviour of carbon dioxide (CO₂) and methane (CH₄) emissions at the surface and below the soil cover in an industrial waste landfill under anaerobic operating conditions was evaluated for six years. This landfill contained gypsum board waste and incineration ash - a practice currently allowed because of a change in Japanese regulations. The CO₂ and CH₄ fluxes decreased throughout the six years of the survey. Almost all of the survey points exhibited fractions of CH₄ in landfill gas emissions of <0.5 (mean values: 0.0-0.1 [surface], 0.0-0.3 [subsurface]) under anaerobic conditions. In addition, a relatively high first-order reaction rate constant for the landfill gas emissions (0.3 year^-1) was observed. The landfill leachate showed a relatively high sulphate ion (SO₄ ^2-) concentration, although other environmental conditions, such as the pH, oxidation-reduction potential and ammonium concentration, were not at levels that could have inhibited CH₄ production. These findings suggest that the low fractions could have been related to the lower amounts of CH₄ generation caused by competition between methanogens and sulphate-reducing bacteria (SRB). Therefore, SRB could play a major role in the degradation of organic carbon in the landfill.

Ferric citrate, nitrate, saponin and their combinations affect in vitro ruminal fermentation, production of sulphide and methane and abundance of select microbial populations

AIMS

This study investigated the effects of ferric citrate, nitrate and saponin, both individually and in combination, on sulphidogenesis, methanogenesis, rumen fermentation and abundances of select microbial populations using in vitro rumen cultures.

METHODS AND RESULTS

Ferric citrate (50 mg l^-1 ), Quillaja saponin (0·6 g l^-1 ) and sodium nitrate (5 mmol l^-1 ) were used in in vitro ruminal fermentation. Ferric citrate alone, its combination with saponin and/or nitrate lowered the aqueous sulphide concentration and total sulphide production. Methane production was suppressed by nitrate alone (by up to 32·92%), its combination with saponin (25·04%) and with both saponins with nitrate (25·92%). None of the treatments adversely affected feed digestion or rumen fermentation. The population of sulphate-reducing bacteria was increased by nitrate and saponin individually, while that of total Archaea was decreased by nitrate alone and the combination of the three inhibitors.

CONCLUSIONS

Nitrate and its combination with saponin or both ferric citrate and saponin substantially decreased methane production. Most importantly, the decreased methane production was not at the expense of feed digestion or fermentation. Sulphidogenesis from the sulphate present in the high-sulphur diets can be suppressed competitively by ferric citrate, although it was elevated by saponin and nitrate.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study demonstrated that combinations of certain methane inhibitors, which have different mechanisms of antimethanogenic actions or inhibit different guilds of microbes involved in methane production and sulphate reduction, can be more effective and practical than individual inhibitors, not only in mitigating enteric methane emission but also in lowering the risk of sulphur-associated polioencephalomalacia in feedlot cattle fed high sulphur diets.

Magnetic sorbents biomineralization on the basis of iron sulphides

Biomineralization means mineral formation under the influence of organisms. Sulphate-reducing bacteria (SRB) constitute an essential role of iron sulphide minerals precipitation. Their composition involves amorphous, non-stoichiometric or crystalline iron sulphides, weakly or strongly magnetic. Variation in environmental conditions can alter the reactive iron species within the mineral, potentially modifying their magnetic properties. Biogenic iron sulphide minerals can be used as heavy metals and toxic ions adsorbents in soil or water remediation. For these reasons, a series of laboratory-scale iron sulphide synthesis experiments with the aim to study the chemical composition, mineralogy and magnetic properties of iron sulphide precipitates were carried out using SRB under various cultivation mode and nutrient medium composition. Energy-dispersive X-ray analysis (EDX) showed formation of iron sulphides in all biogenic samples and iron phosphates in abiotic controls. Results of X-ray diffraction analysis (XRD) in biomineralized samples confirmed nanocrystalline greigite, mackinawite and sulphur alpha. Magnetic measurements showed that sample prepared by static cultivation without addition of fresh nutrient medium was the most magnetic, magnetic hysteresis of sample formed under semicontinuous mode without any nutrient supply was the lowest. Abiotic samples contained only vivianite and they did not prove any significant response to magnetic field.

Core Sulphate-Reducing Microorganisms in Metal-Removing Semi-Passive Biochemical Reactors and the Co-Occurrence of Methanogens

Biochemical reactors (BCRs) based on the stimulation of sulphate-reducing microorganisms (SRM) are emerging semi-passive remediation technologies for treatment of mine-influenced water. Their successful removal of metals and sulphate has been proven at the pilot-scale, but little is known about the types of SRM that grow in these systems and whether they are diverse or restricted to particular phylogenetic or taxonomic groups. A phylogenetic study of four established pilot-scale BCRs on three different mine sites compared the diversity of SRM growing in them. The mine sites were geographically distant from each other, nevertheless the BCRs selected for similar SRM types. Clostridia SRM related to Desulfosporosinus spp. known to be tolerant to high concentrations of copper were members of the core microbial community. Members of the SRM family Desulfobacteraceae were dominant, particularly those related to Desulfatirhabdium butyrativorans. Methanogens were dominant archaea and possibly were present at higher relative abundances than SRM in some BCRs. Both hydrogenotrophic and acetoclastic types were present. There were no strong negative or positive co-occurrence correlations of methanogen and SRM taxa. Knowing which SRM inhabit successfully operating BCRs allows practitioners to target these phylogenetic groups when selecting inoculum for future operations.

Potential Impact of Diet on Treatment Effect from Anti-TNF Drugs in Inflammatory Bowel Disease

We wanted to investigate the current knowledge on the impact of diet on anti-TNF response in inflammatory bowel diseases (IBD), to identify dietary factors that warrant further investigations in relation to anti-TNF treatment response, and, finally, to discuss potential strategies for such investigations. PubMed was searched using specified search terms. One small prospective study on diet and anti-TNF treatment in 56 patients with CD found similar remission rates after 56 weeks among 32 patients with good compliance that received concomitant enteral nutrition and 24 with poor compliance that had no dietary restrictions (78% versus 67%, p = 0.51). A meta-analysis of 295 patients found higher odds of achieving clinical remission and remaining in clinical remission among patients on combination therapy with specialised enteral nutrition and Infliximab (IFX) compared with IFX monotherapy (OR 2.73; 95% CI: 1.73-4.31, p < 0.01, OR 2.93; 95% CI: 1.66-5.17, p < 0.01, respectively). In conclusion, evidence-based knowledge on impact of diet on anti-TNF treatment response for clinical use is scarce. Here we propose a mechanism by which Western style diet high in meat and low in fibre may promote colonic inflammation and potentially impact treatment response to anti-TNF drugs. Further studies using hypothesis-driven and data-driven strategies in prospective observational, animal and interventional studies are warranted.

A single exposure of sediment sulphate-reducing bacteria to oxytetracycline concentrations relevant to aquaculture enduringly disturbed their activity, abundance and community structure

AIM

Although feed medicated with antibiotics is widely used in animal production to prevent and treat bacterial infections, the effect of these drugs on nontarget anaerobic bacteria is unknown. We aimed to clarify whether a single exposure of sulphate-reducing bacteria (SRB) from a tilapia pond to oxytetracycline (OTC) concentrations relevant to aquaculture impacts their function, abundance and community structure.

METHODS AND RESULTS

To demonstrate changes in SO4(2-) content, SRB abundance, dsrB copy number and SRB diversity, sediment mesocosms were spiked with 5, 25, 50 and 75 mg OTC kg(-1) and examined for 30 days by means of ion chromatography, qPCR, cultivation and fluorescent in situ hybridization (FISH). On day 3, we measured higher SO4(2-) concentrations (ca. two-fold) and a reduction in dsrB copy numbers of approximately 50% in the treatments compared to the controls. After 30 days, a subtle yet measurable enrichment of bacteria from the order Desulfovibrionales occurred in mesocosms receiving ≥ 50 mg OTC kg(-1), notwithstanding that SRB counts decreased two orders of magnitude. OTC was dynamically and reversibly converted into 4-epioxytetracycline and other related compounds in a dose-dependent manner during the experiment.

CONCLUSIONS

A single exposure to rather high OTC concentrations triggered functional and structural changes in a SRB community that manifested quickly and persisted for a month.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study improves our limited knowledge on the ecotoxicology of antibiotics in anaerobic environments.

Detection of Sulphate-Reducing Bacteria and Others Cultivable Facultative Bacteria in Dental Tissues

AIM

To detect for the presence of sulphate-reducing bacteria (SRB) and evaluate the possible association between SRB and cultivable facultative bacterial of oral sites with different periodontal conditions.

METHODS

The study was carried out on 9 samples from different oral sites in 8 patients (two samples were collected from the same patient). Material was collected using modified Postgate E culture medium, indicated for the growth and isolation of SRB. In addition, a reducing solution for anaerobic bacteria was used as a transport solution for facultative bacteria and identified by polymerase chain reaction amplification (PCR) and sequencing of the 16S rRNA gene.

RESULTS

SRB was found in 3 patient samples: the first in a root fragment, the second in a root fragment and a healthy tooth with vertical bone loss and a mobility degree of 3; and the third in a healthy tooth extracted for orthodontic treatment. In the final patient, the cultivable facultative species Lactobacillus casei was identified. Other facultative bacterial species were identified in patient 5 (Kurthia Gibsonii) and patient 7 (Pseudomonas aeruginosa).

CONCLUSIONS

The detection of SRB in different dental tissues with distinct periodontal features demonstrated that new studies need to be developed in order to determine the true role of SRB in the oral microbiota. In addition, it was possible to verify the presence of Lactobacillus casei together with SRB in one sample.