Cultivation and biogeochemical analyses reveal insights into biomineralization caused by piezotolerant iron-reducing bacteria from petroleum reservoirs and their application in MEOR

Interactions between minerals and iron-reducing bacteria under in-situ pressure and temperature conditions play important roles in oil extraction, residual oil methanation, and CO2 storage in petroleum reservoirs. However, the impacts of pressure on dissimilatory iron-reducing bacteria (DIRB) are poorly understood. Herein, the interactions between clay minerals and microbes under elevated hydrostatic pressure conditions were elucidated through enrichment experiments. Bioreduction experiments were performed under hydrostatic pressures of 0.1-40 MPa. Microbial diversity analysis revealed that high pressures significantly increased microbial diversity in petroleum reservoirs, which is helpful for restoring underground ecosystems in situ. The key piezotolerant iron-reducing bacteria in the samples were Shewanella and Flaviflexus. These two genera were isolated for the first time from petroleum reservoirs and identified as piezophiles. The SEM results clearly showed mineral surface dissolution. Moreover, nanoscale secondary minerals were produced during biomineralization. XRD analysis revealed that illite, albite, and clinoptilolite were present after bioreduction. The isolates showed the capacity to inhibit hydro-swelling and prevent plugging-related damage in reservoirs.

Culture-dependent and culture-independent methods reveal microbe-clay mineral interactions by dissimilatory iron-reducing bacteria in an integral oilfield

Fe(III) may be reasonably considered as one of the most important electron acceptors in petroleum reservoir ecosystems. The microbial mineralization of clay minerals, especially montmorillonite, is also of great significance to the exploration of petroleum and gas reservoirs. The bioreduction mechanisms of iron-poor minerals in petroleum reservoirs have been poorly investigated. This study investigated the bioreduction of montmorillonite by dissimilatory iron-reducing bacteria (DIRB) in petroleum reservoirs based on culture-independent and culture-dependent methods. Microbial diversity analysis revealed that Halolactibacillus, Bacillus, Alkaliphilus, Shewanella, Clostridium, and Pseudomonas were the key genera involved in the bioreduction of Fe(III). Through the traditional culture-dependent method, most of the key genera were isolated from the samples collected from petroleum reservoirs. Traditional culture-dependent methods can be used to reveal the metabolic characteristics of microorganisms (such as iron-reduction efficiency) to further elucidate the roles of different species (B. subtilis and B. alkalitelluris) in the environment. Moreover, many species with high iron-reduction efficiencies and relatively low abundances in the samples, such as Tessaracoccus and Flaviflexus, were isolated from petroleum reservoirs for the first time. The combination of culture-dependent and culture-independent methods can be used to further the understanding of the microbial communities and the metabolic characteristics of DIRB in petroleum reservoirs. Structural alterations that occurred during the interactions of microorganisms and montmorillonite were revealed through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The physical and chemical analysis results demonstrated that microorganisms from petroleum reservoirs can dissolve iron-poor montmorillonite and promote the release of interlayer water. The secondary minerals illite and clinoptilolite were observed in bioreduced smectite. The formation of secondary minerals was closely related to the dissolution degrees of minerals based on iron reduction.

nov., isolated from the faeces of the oriental stork, Ciconia boyciana

A novel Gram-stain-positive, non-motile, non-spore-forming, coccobacillus-shaped, strictly aerobic bacterium, designated strain H23T48^T, was isolated from the faecal sample of an oriental stork collected from the Seoul Grand Park Zoo in Seoul, Republic of Korea. Optimal growth of strain H23T48^T was observed at 30-37 °C, pH 8 and with 3 % (w/v) NaCl. 16S rRNA gene sequence-based phylogenetic analysis revealed that strain H23T48^T was closely related to the genus Flaviflexus, with 97.0 and 96.7 % sequence similarities to Flaviflexus salsibiostraticola EBR4-1-2^T and Flaviflexus huanghaiensis H5^T, respectively. Strain H23T48^T possessed MK-9(H₄) as the major menaquinone and C_16 : 0 (42.4 %), C_18 : 1  ω9c (31.3 %) and C_14 : 0 (17.7 %) as the major cellular fatty acids. The polar lipids included phosphatidylglycerol, two unidentified lipids, six unidentified phospholipids and two unidentified glycophospholipids. The amino acid composition of the cell-wall peptidoglycan was l-alanine, l-lysine, d-glutamic acid, l-aspartic acid and glycine. The genomic G+C content of strain H23T48^T is 59.5 mol% and the average nucleotide identity value between H23T48^T and F. salsibiostraticola KCT C33148^T (=EBR4-1-2^T) is 75.5 %. Based on the obtained data, strain H23T48^T represents a novel species of the genus Flaviflexus, for which the name Flaviflexus ciconiae sp. nov. is proposed. The type strain is H23T48^T (=KCTC 49253^T=JCM 33282^T).