An aerobic, methanotrophic bacterium, designated KYG T , was isolated from a forest soil in Germany. Cells of strain KYG T were Gram-negative, non-motile, slightly curved rods that multiplied by binary fission and produced yellow colonies. The cells contained intracellular granules of poly-b-hydroxybutyrate at each cell pole, a particulate methane monooxygenase (pMMO) and stacks of intracytoplasmic membranes (ICMs) packed in parallel along one side of the cell envelope. Strain KYG T grew at pH 5.2-7.2 and 2-33 6C and could fix atmospheric nitrogen under reduced oxygen tension. The major cellular fatty acid was C 18 : 1 v7c (81.5 %) and the DNA G+C content was 61.4 mol%. Strain KYG T belonged to the family Beijerinckiaceae of the class Alphaproteobacteria and was most closely related to the obligate methanotroph Methylocapsa acidiphila B2 T (98.1 % 16S rRNA gene sequence similarity and 84.7 % pmoA sequence similarity). Unlike Methylocapsa acidiphila B2 T , which grows only on methane and methanol, strain KYG T was able to grow facultatively on acetate. Facultative acetate utilization is a characteristic of the methanotrophs of the genus Methylocella, but the genus Methylocella does not produce pMMO or ICMs. Strain KYG T differed from Methylocapsa acidiphila B2 T on the basis of substrate utilization pattern, pigmentation, pH range, cell ultrastructure and efficiency of dinitrogen fixation. Therefore, we propose a novel species, Methylocapsa aurea sp. nov., to accommodate this bacterium. The type strain is KYG T (5DSM 22158 T 5VKM B-2544 T ).All known aerobic methanotrophic bacteria belong to the phyla Proteobacteria or Verrucomicrobia (Op den Camp et al., 2009). The proteobacterial methanotrophs are affiliated to two families of the Alphaproteobacteria (Methylocystaceae and Beijerinckiaceae) and one family of the Gammaproteobacteria (Methylococcaceae). The family Beijerinckiaceae is particularly metabolically diverse and contains obligate and facultative methanotrophs and non-methanotrophic chemoheterotrophs. The two methanotrophic genera in this family, Methylocella and Methylocapsa, are abundant in acidic soils and peats (Dedysh et al., 2001(Dedysh et al., , 2003 and are physiologically distinct from each other. Methylocapsa acidiphila is an obligate methanotroph capable of growth only on one-carbon substrates. It has a particulate methane monooxygenase (pMMO) and an extensive intracytoplasmic membrane (ICM) system (Dedysh et al., 2002). In contrast, Methylocella species are the only known methanotrophs that lack pMMO and use only a soluble methane monooxygenase (sMMO) for methane oxidation. The genus Methylocella contains the first-described facultative methanotrophs and they are capable of growth on a few multicarbon substrates as well as methane (Dedysh et al., 2005). Here, we describe the isolation of a new methanotroph in the family Beijerinckiaceae.Abbreviations: ICM, intracytoplasmic membrane; pMMO, particulate methane monooxygenase; sMMO, soluble methane monooxygenase.The GenBank/EMBL/DDBJ accession num...

Acetate, propionate, and butyrate, collectively referred to as volatile fatty acids (VFA), are considered among the most important electron donors for sulfate-reducing bacteria (SRB) and heterotrophic nitrate-reducing bacteria (hNRB) in oil fields. Samples obtained from a field in the Neuquén Basin, western Argentina, had significant activity of mesophilic SRB, hNRB, and nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB). In microcosms, containing VFA (3 mM each) and excess sulfate, SRB first used propionate and butyrate for the production of acetate, which reached concentrations of up to 12 mM prior to being used as an electron donor for sulfate reduction. In contrast, hNRB used all three organic acids with similar kinetics, while reducing nitrate to nitrite and nitrogen. Transient inhibition of VFA-utilizing SRB was observed with 0.5 mM nitrite and permanent inhibition with concentrations of 1 mM or more. The addition of nitrate to medium flowing into an upflow, packed-bed bioreactor with an established VFA-oxidizing SRB consortium led to a spike of nitrite up to 3 mM. The nitrite-mediated inhibition of SRB led, in turn, to the transient accumulation of up to 13 mM of acetate. The complete utilization of nitrate and the incomplete utilization of VFA, especially propionate, and sulfate indicated that SRB remained partially inhibited. Hence, in addition to lower sulfide concentrations, an increase in the concentration of acetate in the presence of sulfate in waters produced from an oil field subjected to nitrate injection may indicate whether the treatment is successful. The microbial community composition in the bioreactor, as determined by culturing and culture-independent techniques, indicated shifts with an increasing fraction of nitrate. With VFA and sulfate, the SRB genera Desulfobotulus, Desulfotignum, and Desulfobacter as well as the sulfur-reducing Desulfuromonas and the NR-SOB Arcobacter were detected. With VFA and nitrate, Pseudomonas spp. were present. hNRB/NR-SOB from the genus Sulfurospirillum were found under all conditions.

When oil is produced by water injection, sulphide formation (souring) can be stimulated. Souring is often caused by sulphate-reducing bacteria (SRB) which oxidize organic carbon (oil organics) with sulphate in the injection water to CO2 and sulphide. As a result, H2S concentrations in the produced water, oil and gas gradually increase. A consequence can be that the piping infrastructure must be redesigned from sweet to sour service. A relatively novel biotechnology aimed to remedy souring is to add nitrate to the injection water. Nitrate tracks the injection water effectively and its cost allows continuous and field-wide treatment. In a field-wide nitrate injection, the injection water (approximately 3,500 m3/day) was amended continuously with 2.4 mM (150 ppm) nitrate. Three points in the injection water system and 12 production wells were monitored by sampling every 2 to 3 weeks. The concentrations of sulphide, sulphate, nitrate, nitrite and ammonia in injection and produced waters were determined, as well as the activities of nitrate-reducing bacteria (NRB). Field-wide nitrate injection gave a 70% drop of aqueous sulphide within the first 5 weeks, after which the concentration recovered somewhat for the next 20 weeks. The activity of NRB increased throughout this period, indicating the possibility of further decreases in souring in the future. Introduction Microbial production of sulphide by sulphate-reducing bacteria (SRB) in oil reservoirs (i.e. souring) often occurs during secondary oil recovery processes when water is injected to maintain reservoir pressure. Souring is largely perceived to have negative effects because dissolved sulphide (HS−) and precipitated metal sulphides (e.g. FeS) are corrosive towards metal pipes and equipment. Injection of suspended metal sulphides may decrease reservoir injectivity by plugging zones near the injection wellbore, decreasing oil production. Suspended metal sulphides also stabilize oil-water emulsions preventing effective separation of produced water and oil. Hence, souring is highly undesirable from a business and operating point of view, especially when the original facilities were not designed to handle sour production. Souring gives rise to safety concerns regarding the exposure of workers in the field to released hydrogen sulphide and to complaints about odours from surface rights owners and, in urban settings, over the threat to real estate values of a sour service operation on or near residential property.