Indigenous microbial communities in heavy oil show a threshold response to salinity

Imprints of ecological processes in the taxonomic core community: an analysis of naturally replicated microbial communities enclosed in oil

It is widely assumed that a taxonomic core community emerges among microbial communities from similar habitats because similar environments select for the same taxa bearing the same traits. Yet, a core community itself is no indicator of selection because it may also arise from dispersal and neutral drift, i.e. by chance. Here, we hypothesize that a core community produced by either selection or chance processes should be distinguishable. While dispersal and drift should produce core communities with similar relative taxon abundances, especially when the proportional core community, i.e. the sum of the relative abundances of the core taxa, is large, selection may produce variable relative abundances. We analyzed the core community of 16S rRNA gene sequences of 193 microbial communities occurring in tiny water droplets enclosed in heavy oil from the Pitch Lake, Trinidad and Tobago. These communities revealed highly variable relative abundances along with a large proportional core community (68.0 ± 19.9%). A dispersal-drift null model predicted a negative relationship of proportional core community and compositional variability along a range of dispersal probabilities and was largely inconsistent with the observed data, suggesting a major role of selection for shaping the water droplet communities in the Pitch Lake.

Enrichment of microbial consortia for MEOR in crude oil phase of reservoir-produced liquid and their response to environmental disturbance

Developing microbial consortiums is necessary for microbial enhanced oil recovery (MEOR) in heavy crude oil production. The aqueous phase of produced fluid has long been considered an ideal source of microorganisms for MEOR. However, it is recently found that rich microorganisms (including hydrocarbon-degrading bacteria) are present in the crude oil phase, which is completely different from the aqueous phase of produced fluid. So, in this study, the microbial consortia from the crude oil phase of produced fluids derived from four wells were enriched, respectively. The microbial community structure during passage was dynamically tracked, and the response of enriched consortia to successive disturbance of environmental factors was investigated. The results showed the crude oil phase had high microbial diversity, and the original microbial community structure from four wells was significantly different. After ten generations of consecutive enrichment, different genera were observed in the four enriched microbial consortia, namely, Geobacillus, Bacillus, Brevibacillus, Chelativorans, Ureibacillus, and Ornithinicoccus. In addition, two enriched consortia (eG1614 and eP30) exhibited robustness to temperature and oxygen perturbations. These results further suggested that the crude oil phase of produced fluids can serve as a potential microbial source for MEOR.

Characteristics of microbiota, core sulfate-reducing taxa and corrosion rates in production water from five petroleum reservoirs in China

Microbial diversity and activities in petroleum reservoir systems can be altered by water-flooding operation, but the current understanding of the mechanism for such changes in microbial composition characteristics and community is inadequate. In this study, microbial communities especially functional groups in production water from five petroleum reservoirs in China were investigated by chemical and molecular biological analyses. The dominant and core phyla in the five oil reservoirs were Proteobacteria, Deferribacterota, Firmicutes, Desulfobacterota, Euryarchaeota and Thermoplasmatota. At the genus level, the dominant taxa in each petroleum reservoir were different, and not all of the dominant genera were the core members across the five oil reservoirs. The microbiologically influenced corrosion (MIC) were investigated for the functional groups in each production water. The corrosion rates in production water were higher than controls with a positive correlation to the abundances of sulfate-reducing prokaryotes (SRP). The SRP diversity based on the aprA and dsrA gene analysis showed that obvious differences were evident between onshore (JS, SL, DQ and XJ) and offshore (BS) oilfields. The core SRP taxa in onshore oilfields were Desulfomicrobium and Desulfovibrio, also with Desulfotomaculum in medium/low-temperature oil reservoirs (DQ and XJ), but in high-temperature petroleum reservoirs (JS, BS and SL), Archaeoglobus, Thermodesulfobacterium and Thermodesulfovibrio were the core groups. Statistical analysis indicated that temperature, electron acceptors and donors showed significant influence on the SRP community. This research reveals the characteristics of microbial and functional community as well as their interaction mechanism on corrosion in petroleum reservoir environments, and will improve industrial bio-control and management of MIC in oilfields.

Microbial communities in crude oil phase and filter-graded aqueous phase from a Daqing oilfield after polymer flooding

AIMS

The aim was to characterize indigenous microorganisms in oil reservoirs after polymer flooding (RAPF).

METHODS

The microbial communities in the crude oil phase (Oil) and in the filter-graded aqueous phases Aqu0.22 (>0.22 μm) and Aqu0.1 (0.1~0.22 μm) were investigated by 16S rRNA gene high-throughput sequencing.

RESULTS

Indigenous microorganisms related to hydrocarbon degradation prevailed in the three phases of each well. However, obvious differences of bacterial compositions were observed among the three phases of the same well and among the same phase of different wells. The crude oil and Aqu0.22 shared many dominant bacteria. Aqu0.1 contained a unique bacterial community in each well. Most bacteria in Aqu0.1 were affiliated to culturable genera, suggesting that they may adapt to the oil reservoir environment by reduction of cell size. Contrary to the bacterial genera, archaeal genera were similar in the three phases but varied in relative abundances. The observed microbial differences may be driven by specific environmental factors in each oil well.

CONCLUSIONS

The results suggest an application potential of microbial enhanced oil recovery (MEOR) technology in RAPF. The crude oil and Aqu0.1 contain many different functional microorganisms related to hydrocarbon degradation. Both should not be overlooked when investing and exploring the indigenous microorganisms for MEOR.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work facilitates the understanding of microbial community structures in RAPF and provides information for microbial control in oil fields.

Inhibition of sulfate-reducing bacteria with formate

Despite hostile environmental conditions, microbial communities have been found in µL-sized water droplets enclosed in heavy oil of the Pitch Lake, Trinidad. Some droplets showed high sulfate concentrations and surprisingly low relative abundances of sulfate-reducing bacteria in a previous study. Hence, we investigated here whether sulfate reduction might be inhibited naturally. Ion chromatography revealed very high formate concentrations around 2.37 mM in 21 out of 43 examined droplets. Since these concentrations were unexpectedly high, we performed growth experiments with the three sulfate-reducing type strains Desulfovibrio vulgaris, Desulfobacter curvatus, and Desulfococcus multivorans, and tested the effects of 2.5, 8 or 10 mM formate on sulfate reduction. Experiments demonstrated that 8 or 10 mM formate slowed down the growth rate of D. vulgaris and D. curvatus and the sulfate reduction rate of D. curvatus and D. multivorans. Concerning D. multivorans, increasing formate concentrations delayed the onsets of growth and sulfate reduction, which were even inhibited completely while formate was added constantly. Contrary to previous studies, D. multivorans was the only organism capable of formate consumption. Our study suggests that formate accumulates in the natural environment of the water droplets dispersed in oil and that such levels are very likely inhibiting sulfate-reducing microorganisms.