Influence of oxygen on the vinyl acetate elimination pathway and microbial community structure of methanogenic sludge.

Methanogenic-aerobic coupled processes were used to biological degradation of vinyl acetate (VA) to provide evidence of oxygen role for their complete elimination from different angles. First, physiological characterization of a continuous methanogenic-aerobic reactor fed by VA and glucose (G) showed that by adding G, the VA got 100% hydrolyzed to acetate, and then, by adding 1 mg·L-1 ·d-1 of dissolved oxygen (DO), this acetate got methanized by 40% and aerobically mineralized by 60%. Second, batch assays in the presence and absence of sodium azide suggest that VA at different concentrations was eliminated by both anaerobic and aerobic metabolic pathways, because without azide and in the presence of 1 mg DO·L-1 increased methane and carbon dioxide formation rates at 80% and 75%, respectively. Finally, microbial population dynamics analysis of the reactor by DGGE-sequencing highlighted that Brevibacillus agri (aerobic) and Methanosarcina barkeri (anaerobic) were identified as responsible for VA elimination by up to 98.6%. PRACTITIONER POINTS: Vinyl acetate is removed by simultaneous methanation and aerobic respiration. Methanosarcina barkeri and Brevibacillus agri removed up to 99% of vinyl acetate. DO and VA have a selective effect on the metabolism and population dynamics.

A Novel Method to Reveal a Ureolytic Biofilm Attachment and In Situ Growth Monitoring by Electrochemical Impedance Spectroscopy.

The formation of biofilms capable of efficiently carrying out ureolysis is of fundamental importance in several biotechnological systems such as urinary tract infections, building materials and municipal wastewater treatment. This work proposes a straightforward method for the formation of a ureolytic biofilm attached to graphite. The proposed strategy reduced the time needed to complete ureolysis to 3 days instead of 16 days required in suspension culture. To confirm the formation of a ureolytic biofilm, scanning electron microscopy and confocal laser scanning microscopy studies were employed ex situ. However, it is imperative to analyse the biofilm by direct non-invasive techniques. Accordingly, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were used as in situ monitoring techniques. The reduction in OCP from - 0.01 to - 0.2 V vs. Ag/AgCl and the increase in capacitance from 200 to 260 µF cm-2 were related to biofilm attachment. To the best of our knowledge, this is the first time in which a ureolytic biofilm attachment has been analysed by EIS. The increase in the biomass from 0.04 to 2.81 µm3 µm-2 and in average thickness from 10.19 to 32.78 µm was related to biofilm maturation.

Characterization of bacterial community associated to biofilms of corroded oil pipelines from the southeast of Mexico.

Microbial communities associated to biofilms promote corrosion of oil pipelines. The community structure of bacteria in the biofilm formed in oil pipelines is the basic knowledge to understand the complexity and mechanisms of metal corrosion. To assess bacterial diversity, biofilm samples were obtained from X52 steel coupons corroded after 40 days of exposure to normal operation and flow conditions. The biofilm samples were directly used to extract metagenomic DNA, which was used as template to amplify 16S ribosomal gene by PCR. The PCR products of 16S ribosomal gene were also employed as template for sulfate-reducing bacteria (SRB) specific nested-PCR and both PCR products were utilized for the construction of gene libraries. The V3 region of the 16S rRNA gene was also amplified to analyse the bacterial diversity by analysis of denaturing gradient gel electrophoresis (DGGE). Ribosomal library and DGGE profiles exhibited limited bacterial diversity, basically including Citrobacter spp., Enterobacter spp. and Halanaerobium spp. while Desulfovibrio alaskensis and a novel clade within the genus Desulfonatronovibrio were detected from the nested PCR library. The biofilm samples were also taken for the isolation of SRB. Desulfovibrio alaskensis and Desulfovibrio capillatus, as well as some strains related to Citrobacter were isolated. SRB consists in a very small proportion of the community and Desulfovibrio spp. were the relatively abundant groups among the SRB. This is the first study directly exploring bacterial diversity in corrosive biofilms associated to steel pipelines subjected to normal operation conditions.

Petrotoga mexicana sp. nov., a novel thermophilic, anaerobic and xylanolytic bacterium isolated from an oil-producing well in the Gulf of Mexico.

A novel anaerobic, thermophilic, xylanolytic, motile rod-shaped bacterium with a sheath-like outer structure (toga) was isolated from a Mexican oil well in the Gulf of Mexico. Strain MET12T was a Gram-negative bacterium, reducing elemental sulfur, thiosulfate and sulfite to hydrogen sulfide. Its optimum growth conditions were 55 degrees C, pH 6.6, 3% NaCl and 0.15% MgCl2.6H2O. The DNA G+C content was 36.1 mol%. Phylogenetically, strain MET12T was related to members of genus Petrotoga, with similarities to Petrotoga mobilis, Petrotoga sibirica, Petrotoga miotherma and Petrotoga olearia varying from 97.6 to 98.8%. However DNA-DNA relatedness values between these species and strain MET12T were lower than 70%. As strain MET12T (=DSM 14811T=CIP 107371T) was genomically and phenotypically different from existing Petrotoga species, it is proposed as the type strain of a novel species, Petrotoga mexicana sp. nov.

Desulfovibrio capillatus sp. nov., a novel sulfate-reducing bacterium isolated from an oil field separator located in the Gulf of Mexico.

A new spirilloid sulfate-reducing bacterium designated strain MET2(T) (T=type strain), was isolated from a Mexican oil field separator. Electron microscopy revealed a Gram-negative cell wall consisting of a 150nm thick undulating outer membrane. Strain MET2(T) appeared singly or in long chains and was actively motile with a corkscrew-like motion. The isolate grew optimally at 40 degrees C, pH 7.4 and 3% NaCl in a medium containing lactate, thiosulfate and yeast extract. Sulfate, sulfite, thiosulfate, and elemental sulfur served as electron acceptors but not nitrate or fumarate. Lactate, pyruvate and H(2) (with acetate as carbon source) were used as electron donors. Pyruvate was fermented. Desulfoviridin and cyt c were present. The G+C content of the DNA was 58.7mol%. Phylogenetic analysis based on 16S rDNA sequencing showed that strain MET2(T) was a member of the genus Desulfovibrio with "D. gracilis" and D. longus being its closest relatives (similarities of 98.3% and 97.1%, respectively). However, DNA-DNA hybridization studies indicated poor homologies (values <70%) with both species. On the basis of genotypic, phenotypic, and phylogenetic characteristics, strain MET2(T) (=DSM14982(T)=CIP107483(T)) is proposed as the type strain of a new species, Desulfovibrio capillatus sp. nov. GenBank accession number for the 16S rDNA sequence for MET2(T) is AY176773.