A transcriptional Regulator Gar Regulates the Growth and Virulence of Xanthomonas oryzae pv. oryzae.

Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of bacterial blight, one of the most devastating diseases of rice. Pathogenic bacteria possess numerous transcriptional regulators to participate in the regulation of cellular processes. Here, we identified a transcriptional regulator Gar (PXO_RS11965) that is involved in regulating the growth and virulence of Xoo. Notably, the knockout of gar in Xoo enhanced bacterial virulence to the host rice. RNA-sequencing analysis and quantitative ß-glucuronidase (GUS) assay indicated that Gar positively regulates the expression of a σ54 factor rpoN2. Further experiments confirmed that overexpression of rpoN2 restored the phenotypic changes caused by gar deletion. Our research revealed that Gar influences bacterial growth and virulence by positively regulating the expression of rpoN2.

Transcriptional regulator Sar regulates the multiple secretion systems in Xanthomonas oryzae.

Xanthomonas oryzae pv. oryzae (Xoo) is a notorious plant pathogen that causes leaf blight of rice cultivars. The pathogenic bacteria possess numerous transcriptional regulators to regulate various biological processes, such as pathogenicity in the host plant. Our previous study identified a new master regulator PXO_RS20790 that is involved in pathogenicity for Xoo against the host rice. However, the molecular functions of PXO_RS20790 are still unclear. Here, we demonstrate that transcriptional regulator Sar (PXO_RS20790) regulates multiple secretion systems. The RNA-sequencing analysis, bacterial one-hybrid assay, and electrophoretic mobility shift assay revealed that Sar enables binding of the promoters of the T1SS-related genes, the avirulence gene, raxX, and positively regulates these genes' expression. Meanwhile, we found that Sar positively regulated the T6SS-1 clusters but did not regulate the T6SS-2 clusters. Furthermore, we revealed that only T6SS-2 is involved in interbacterial competition. We also indicated that Sar could bind the promoters of the T3SS regulators, hrpG and hrpX, to activate these two genes' transcription. Our findings revealed that Sar is a crucial regulator of multiple secretion systems and virulence.

Study on the Effect of Threshold Pressure Gradient on Remaining Oil Distribution in Heavy Oil Reservoirs.

Due to the spatial network structure, heavy oil has a high threshold pressure gradient when it flows through porous media, and the threshold pressure gradient plays a crucial role in the distribution of remaining oil. In previous study, the common methods to measure the threshold pressure gradient include the microflow-established differential pressure (MFEDP) method, capillary equilibrium method, and the percolation curve fitting method. In this study, a sample from the SZ36-1 oilfield was analyzed for the basic physical properties based on the comparison of the previous measurement to study the influence of mobility on the threshold pressure gradient and then an independently developed numerical simulator was established to study the effect of the threshold pressure gradient on the remaining oil distribution considering the permeability range, crude oil viscosity, well network deployment, well spacing, and fluid recovery rate. The results show that the SZ36-1 oilfield fluid belongs to Bingham fluids with yield stress and the mobility having an exponent relation to the threshold pressure gradient based on the measurement of the MFEDP method. Considering the threshold pressure gradient of heavy oil, the uneven distribution of remaining oil is intensified and the remaining oil is enriched. This study provides a reference for efficient development of heavy oil reservoirs.

Study on the Influence of Different Factors on Spontaneous Oil Recovery of Nanosurfactants in a Tight Reservoir.

The surface of a tight reservoir appears to be oil-wet or mixed-type wet upon soaking in crude oil for a long time, and the yield decreases rapidly after fracturing under the influence of capillary force. The oil sweep efficiency affected by many factors such as formation water dilution, salinity, crude oil type, temperature, and pressure can be enhanced by adding nanosurfactants into the fracturing fluid, so it is necessary to study the influence of different factors on the spontaneous imbibition replacement efficiency of nanosurfactants. In this study, the basic properties of nanosurfactants such as particle size, oil-water interfacial tension (IFT), and the wetting modification effect were tested, and the influence of surfactant type, concentration, temperature, and pressure on imbibition replacement efficiency was studied. The main conclusions are as follows: (1) The particle size of the nanosurfactant that was synthesized by a microemulsion method is 12-21 nm, which indicated good injectability in tight cores. Moreover, the IFT values between the crude oil and five kinds of 0.30 wt % nanosurfactants were all lower than 0.15 mN/m, and nanosurfactant C had the best wetting modification effect with increasing the contact angle by 100.30°. (2) The type and concentration of surfactant have a certain influence on imbibition replacement efficiency, and appropriate concentration of anionic nanosurfactant is beneficial to enhancing the imbibition replacement efficiency. The imbibition replacement efficiency of 0.30 wt % anionic surfactant C solution is higher than that of nonionic and cationic surfactant solutions, and the imbibition replacement efficiency is as high as 33.386% under NTP. (3) The nanosurfactant in brine is prone to forming fine emulsified oil droplets with crude oil and activates the oil droplets in the small pores to enhance the imbibition replacement efficiency. The crude oil type, temperature, and pressure can influence imbibition replacement efficiency, and the influence of crude oil type and temperature is greater than that of pressure. This work further studies the influencing factors of imbibition replacement efficiency.

Elucidation of the Pathogenicity-Associated Regulatory Network in Xanthomonas oryzae pv. oryzae.

Xanthomonas is a notorious plant pathogen causing serious diseases in hundreds of plant hosts. Xanthomonas species are equipped with an array of signal transduction systems that regulate gene expression to survive in various harsh environments and successfully infect hosts. Although certain pathogenicity-associated regulators have been functionally characterized, signal transduction systems always function as a regulatory network which remains to be elucidated in Xanthomonas This study used a systematic approach to characterize all identified pathogenicity-associated regulators in Xanthomonas oryzae pv. oryzae (Xoo), including a transcriptional regulator with unknown function, and their interactive regulatory network. RNA sequencing was used in elucidating the patterns of the 10 pathogenicity-associated regulators identified. Results revealed that each pathogenicity-associated regulator has cross talk with others and all these regulators function as a regulatory network, with VemR and PXO_RS20790 being the master pathogenicity-associated regulators and HrpX being the final executant. Moreover, regulome analysis showed that numerous genes other than genes in pathogenicity islands are finely regulated within the regulatory network. Given that most of the pathogenicity-associated regulators are conserved in Xanthomonadales, our findings suggest a global network of gene regulation in this evolutionarily conserved pathogen. In conclusion, our study provides essential basic information about the regulatory network in Xoo, suggesting that this complicated regulatory network is one of the reasons for the robustness and fitness of Xanthomonas spp.IMPORTANCE The host plant infection process of pathogenic bacteria is a coordinating cellular behavior, which requires dynamic regulation at several levels in response to variations in host plants or fluctuations in the external environment. As one of the most important genera of plant-pathogenic bacteria, Xanthomonas has been studied as a model. Although certain pathogenicity-associated regulators have been functionally characterized, interactions among them remain to be elucidated. This study systematically characterized pathogenicity-associated regulators in Xoo and revealed that cross talk exists among pathogenicity-associated regulators and function as a regulatory network in which a hierarchy exists among the regulators. Our study elucidated the landscape of the pathogenicity-associated regulatory network in Xanthomonas, promoting understanding of the infection process of pathogenic bacteria.