Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Special Distribution of Crude Oil in the Lucaogou Formation in Jimusaer Sag and Genetic Analysis of Its Physical Difference

The shale oil of the Lucaogou Formation in the Jimusaer Sag of the Junggar Basin was divided into two sweet spots for exploration and development. Crude oil in the upper and lower sweet spots comes from the upper and lower source rocks. After years of exploration, it has been found that the crude oil in the lower sweet spot has worse physical properties than that of the upper sweet spot. In this study, through the physical and geochemical analysis of crude oil in the upper and lower sweet spots, combined with the organic petrological observation of the upper and lower source rocks, the cause of the poor physical properties of the crude oil in the lower sweet spot has been identified. n-Alkanes in the saturated hydrocarbons of crude oil in the upper and lower sweet were complete while odd-to-even predominance was evident, indicating that the poor physical properties of the crude oil are unrelated to biodegradation. In addition, the correlation between the biogenic parameters and the physical properties of crude oil was analyzed, finding that the difference in crude oil is mainly related to the composition of biogenic precursors of upper and lower source rocks. Combined with organic petrological observation, the lower source rock was found to be rich in telalginite (green algae), which is therefore the primary reason for the difference in physical properties. In comparing results from the characteristics of crude oil biomarkers from both the upper and lower sweet spots, crude oils in the upper sweet spot are similar to each other, indicating that the enrichment of crude oil has experienced a certain migration. In contrast, the differences in biomarkers between the crude oils of the lower sweet spot were relatively large and changed regularly with depth, suggesting the self-generated and self-stored characteristics of crude oil enrichment. At the same time, it was found that the crude oil in the lower sweet spot is also affected by the maturity of adjacent source rocks under the condition of a consistent parent material source. Overall, it was determined that the lower the maturity of source rocks, the poorer the physical property of the crude oil produced

Chitosan Reduces Damages of Strawberry Seedlings under High-Temperature and High-Light Stress

High-temperature and high-light are the main adversity stresses faced by strawberry seedlings and open-field cultivation in summer. Chitosan (CTS) is widely used in agriculture as a soil amendment, plant growth regulator, and promoter of cold resistance. However, the effects of CTS on strawberry seedlings under the combined stress of high-temperature and high-light are unclear. This study aimed to determine the effect of CTS on strawberry seedlings under the combined stress of high-temperature and high-light. In this study, Xuelixiang strawberry was used as the experimental plant material. The leaves were sprayed with 100 mg/Kg CTS or deionized aqueous solution and placed under high-temperature and high-light (38 °C, 1800 μ mol·m−2·s−1, respectively) for 8 h. In addition, a suitable temperature and light (23 °C, 400 μ mol·m−2·s−1, respectively) was sprayed with deionized water as a control. The results showed that compared with non-CTS treatment, the chlorophyll (Chl) content in strawberry plants increased by 16.9% after CTS treatment; the net CO2 exchange (Pn) increased by 74.9%; and the maximum photochemical efficiency increased by 20.1%. In addition, CTS treatment increased the content of antioxidants; increased osmotic adjustment substances; improved the activity of reduced glutathione with reduced ascorbic acid (AsA-GSH) circulating antioxidant enzymes; removed reactive oxygen species in plants in time; and reduced the damage of reactive oxygen species to photosynthetic organs and cell membranes, thereby reducing high-temperature and high-light injury to strawberry seedlings. This study shows that CTS can improve the negative effects of high-temperature and high-light stress on strawberry seedlings

Reason for abnormally high drying coefficient of natural gas in Cainan area, Junggar Basin

In order to clarify the reason for generally high drying coefficient of natural gas in Cainan area of the Junggar Basin and find out the law of natural gas migration and accumulation, the analysis of natural gas components and carbon isotopes, rock mineral composition in reservoir, bulk carbon and oxygen isotope of calcite, and laboratory hydrocarbon oxidation simulation experiments were carried out. The Jurassic natural gas in Cainan area is dominated by methane, with drying coefficient of generally greater than 0.95, and δ13C1 value of basically greater than -32‰. Among C7 light hydrocarbons, methylcyclohexane is dominant, with methylcyclohexane index of greater than 50%, indicating that natural gas in the study area came from high-over mature Carboniferous source rocks. Judging from natural gas migration identification index of ln(C1/C2) with δ13C1-δ13C2, from well block Cai-47 to well block Cai-31, and then to well block Cai-003, ln(C1/C2) values gradually increased, but δ13C1-δ13C2 values did not show a trend of decreasing or increasing, indicating that migration or maturity is not the main controlling factor for the changes of natural gas composition and carbon isotope in the study area. Hydrocarbon thermal oxidation simulation experiments showed that alcohols in oil and gas were oxidized by MnO2 to generate methane and carbon dioxide at 125℃, and methane could only be oxidized to generate CO2 when the temperature reached 200℃, thus changing the composition of oil and gas and increasing methane content in natural gas. Using backscattered electron probe technology, it was found that there are two types of calcite in Jurassic dry gas interval in the study area. One type of calcite has a high Mn content, which can be as high as 3%. It appears bright orange and orange under cathodoluminescence. In addition, the bulk carbon isotope of calcite is negatively biased, which is 5‰-10‰ more negative than that of normal calcite. The higher content of Mn in calcite, the more negative of bulk carbon isotope, confirming that there is widespread weak oxidation of hydrocarbons in the Jurassic dry gas interval in Cainan area. Comprehensive analysis suggested that the reason for abnormally high drying coefficient of Jurassic natural gas in Cainan area is that the humic source rocks have undergone high-over mature evolution to generate natural gas that accumulated in Jurassic reservoirs rich in oxidizing minerals. Then the oxidation of hydrocarbons caused methane content in natural gas to increase further, resulting in a generally high drying coefficient of natural gas

Chemometric Classification and Geochemistry of Crude Oils in the Eastern Fukang Sag, Junggar Basin, NW China

Thirty oil samples collected from the eastern Fukang Sag were analyzed geochemically for their biomarkers and carbon isotopic compositions. The chemometric methods of principal component analysis and hierarchical cluster analysis, employed to thirteen parameters indicating source and depositional environment, classified the oil samples into three genetically distinct oil families: Family A oils were mainly derived from lower aquatic organisms deposited in a weakly reducing condition of fresh–brackish water, Family B oils came from a source containing predominantly terrigenous higher-plant organic matter laid down in an oxidizing environment of fresh water, and Family C oils received sources from both terrigenous and marine organic matter deposited in a weakly oxidizing to oxidizing environment of brackish water. Indirect oil–source correlations implied that Family A oils were probably derived from Permian source rocks, Family B oils originated mainly from Jurassic source rocks, and Family C oils had a mixed source of Carboniferous and Permian. Biomarker maturity parameters revealed that all three families of oils were in the mature stage. However, Family A oils were relatively less mature than Family B and Family C oils

Multivariate Statistical Analysis Reveals the Heterogeneity of Lacustrine Tight Oil Accumulation in the Middle Permian Jimusar Sag, Junggar Basin, NW China

Tight oil and gas accumulation commonly has heterogeneities within the reservoir formation. This heterogeneity, however, is hard to investigate by conventional geological and (organic) geochemical tools and thus is critical and challenging to study. Here, we attempted multivariate statistical analysis to reveal the heterogeneity based on a case study in the lacustrine tight oil accumulation in the middle Permian Lucaogou Formation of the Jimusar sag, Junggar Basin, NW China. Clustering heat maps and multi-dimensional scaling analysis revealed the heterogeneity of tight oil accumulation. The heterogeneity is reflected by the complex relationship between the two reservoir sweet spots as well as the oil migration and accumulation vertically and spatially, rather than the previous thoughts that it is a closed system associated with proximal hydrocarbon accumulation patterns. Multiple biomarkers show that the source rocks and reservoirs have similar characteristics in the lower part of the formation, reflecting a proximal hydrocarbon accumulation pattern in the lower sweet spot (near-source accumulation, abbreviated as NA). This represents a relatively closed system. However, the upper sweet spot and the middle section mudstone sequence intervening the two sweet spots are not a completely closed system in a strict sense. These sequences can be divided into three tight oil segments, i.e., lower, middle, and upper from deep to shallow. The lower segment is sited in the lower part of the middle section mudstone sequence. The middle segment is composed of the upper part of the middle section mudstone sequence and the lower part of the upper sweet spot. The upper segment is composed of the upper part of the upper sweet spot and the overlying upper Permian Wutonggou Formation reservoirs. Oils generated in the lower segment migrated vertically to upper sweet spot reservoirs through faults/fractures, and laterally to distal reservoirs. Oils generated in the middle segment were preserved in reservoirs of the upper sweet spot. Oils in the upper segment require accumulation by vertical and lateral migration through faults/fractures. As such, the tight oil accumulation is complex in the Lucaogou Formation. From base to top, the accumulation mechanisms in the Lucaogou Formation were NA, VLMA (vertical and lateral migration and accumulation), NA and VLMA, thereby showing strong heterogeneities. Our data suggest that these processes might be typical of tight oil accumulations universally, and are important for future exploration and exploitation in the region to consider the heterogeneities rather than a closed system. The multivariate statistical analysis is an effective tool for investigating complex oil-source correlations and accumulation in petroleum basins

Experimental study on hydrocarbon generation and expulsion characteristics of shale with different source-reservoir structures in Lucaogou Formation, Jimsar Sag, Junggar Basin

The Permian Lucaogou Formation in the Jimusar Sag in the east of the Junggar Basin is a typical continental shale oil series in China. Employing the semi-closed thermal simulation system, an experimental study on hydrocarbon generation and expulsion of shale with different source-reservoir structures was carried out to explore the efficiency and composition characteristics of hydrocarbon generation and expulsion of shale in the Permian Lucaogou Formation with different source-reservoir structures so as to provide reference for the enrichment rule of shale hydrocarbon and the fine evaluation of "sweet spots". The experimental results show that thick reservoir interbedded with thin source rock is more conducive to hydrocarbon expulsion and features the highest hydrocarbon expulsion efficiency, while thin source rock interbedded with thin reservoir features slightly lower hydrocarbon expulsion efficiency, and thick source rock interbedded with thin reservoir features the lowest hydrocarbon expulsion efficiency. When reservoir lithology is clastic rock, the hydrocarbon expulsion efficiency of thick reservoir interbedded with thin source rock, thin source rock interbedded with thin reservoir, and thick source rock interbedded with thin reservoir are 35.6%, 30.7%, and 25.6%, respectively. When reservoir lithology is carbonate rock, the hydrocarbon expulsion efficiency of these three combinations are 27.4%, 27.5%, and 12.3%, respectively. Combined with composition of expelled hydrocarbon, received hydrocarbon in reservoir, and retained hydrocarbon in source rock, it is found that received hydrocarbon in reservoir rock is mainly supplied by neighboring sources, and the farther away from source-reservoir interface, the less relevant relationship between source rock and hydrocarbon in reservoir. Hydrocarbon in reservoir is supplied by lower adjacent source rock in thick reservoir interbedded with thin source rock, and the received hydrocarbon in upper clastic reservoir is 10.7 mg/g, while received hydrocarbon in lower clastic reservoir is only 1.4 mg/g. The thick source rock interbedded with thin reservoir is mainly self-generated and self-stored, and the content of retained hydrocarbon in source rock is high, the received hydrocarbon in upper clastic reservoir is 6.0 mg/g, while retained hydrocarbon in source rock is 21.1 mg/g. Hydrocarbon in reservoir is mainly supplied by lower adjacent source rock and partly from its own source rock in thin source rock interbedded with thin reservoir. There is no significant difference between source rock and reservoir rock in the extraction family, with the content of saturated hydrocarbon in the range of 22.8%-33.0%, aromatics in the range of 6.2%-15.1%, and non-hydrocarbon and asphaltene in the range of 28.5%-41.1% and 21.0%-30.0%. Moreover, different reservoir lithology has relatively weak influence on hydrocarbon generation and expulsion efficiency, and the hydrocarbon-bearing heterogeneity is weak in thin source rock interbedded with thin reservoir. From the perspective of hydrocarbon generation and expulsion efficiency of shale with different source-reservoir structures, thick reservoir interbedded with thin source rock and thin source rock interbedded with thin reservoir are the favorable combinations for hydrocarbon exploration in the shale of the Lucaogou Formation