Members of Methanocellales are widespread in paddy field soils and play the key role in methane production. These methanogens feature largely in these organisms' adaptation to low H 2 and syntrophic growth with anaerobic fatty acid oxidizers. The adaptive mechanisms, however, remain unknown. In the present study, we determined the transcripts of 21 genes involved in the key steps of methanogenesis and acetate assimilation of Methanocella conradii HZ254, a strain recently isolated from paddy field soil. M. conradii was grown in monoculture and syntrophically with Pelotomaculum thermopropionicum (a propionate syntroph) or Syntrophothermus lipocalidus (a butyrate syntroph). Comparison of the relative transcript abundances showed that three hydrogenase-encoding genes and all methanogenesis-related genes tested were upregulated in cocultures relative to monoculture. The genes encoding formylmethanofuran dehydrogenase (Fwd), heterodisulfide reductase (Hdr), and the membrane-bound energy-converting hydrogenase (Ech) were the most upregulated among the evaluated genes. The expression of the formate dehydrogenase (Fdh)-encoding gene also was significantly upregulated. In contrast, an acetate assimilation gene was downregulated in cocultures. The genes coding for Fwd, Hdr, and the D subunit of F 420 -nonreducing hydrogenase (Mvh) form a large predicted transcription unit; therefore, the Mvh/Hdr/Fwd complex, capable of mediating the electron bifurcation and connecting the first and last steps of methanogenesis, was predicted to be formed in M. conradii. We propose that Methanocella methanogens cope with low H 2 and syntrophic growth by (i) stabilizing the Mvh/Hdr/Fwd complex and (ii) activating formatedependent methanogenesis.T he 16S rRNA gene of a new type of methanogen, Methanocellales, was discovered in 1998 from the surface of rice root (1). The 16S rRNA gene sequences were found phylogenetically branching off between Methanosarcinaceae and Methanomicrobiales. An enrichment culture at 50°C revealed that these organisms contained the methyl-coenzyme M (CoM) reductase-encoding genes, confirming their nature as methanogenic archaea (2, 3). They were found to be widespread in rice field soils and the environment, including desert soil (4-7). Due to the difficulty of cultivation, many molecular studies were conducted to characterize their ecological functions prior to isolation into pure culture. The application of stable isotope probing technology showed that these organisms outcompeted other methanogens under low-H 2 conditions (8). This result suggested, for the first time, that these methanogens are intrinsically adaptive to low H 2 . Moreover, they were found to play the key role in CH 4 production from rootderived material in the rice rhizosphere in situ, illustrating their ecological significance and niche specificity (9).More evidence for the adaptation of Methanocellales to low H 2 came from the investigations of syntrophic oxidation of shortchain fatty acids (10-14). In the investigations of syntrophic oxidations...

Abstract：Dependent on automatically generated unstructured grids, a comprehensive computational fluid dynamics (CFD)numerical simulation is performed to analyze the influence of nozzle geometry on the internal flow characteristics of a multi-hole diesel injector with the multi-phase flow model based on Eulerian multi-fluid method. The diesel components in nozzle are considered as two continuous phases, diesel liquid and diesel vapor respectively. Considering that both of them are fully coupled and interpenetrated, separate sets of governing equations are established and solved for each phase. The geometric parameters mainly include the length and exit diameter of nozzle, the rounded radius at inlet of nozzle orifice and the angle between axis of injector and axis of nozzle orifice, and they are individually taken into account to analyze the impact on the cavitating flow in nozzle. The results show that the geometrical characteristics of nozzle have a strong influence on the volume fraction of diesel vapor in nozzle and the outlet flow velocity of injector. So cavitation in nozzle orifice should not be neglected for the in-cylinder fuel atomization process, especially for the primary break-up of liquid jet.Fuel injection plays an important role in the performance and emissions of internal combustion engine, especially for modern diesel engine and gasoline direct injection (GDI) engine. Direct injection engines exhibit high potential for the reduction of fuel consumption, and thus more and more automobile manufacturers start to use high-pressure fuel injectors. The purpose of high inlet pressure is to produce high injection velocity which results in an efficient atomization process with small and dispersed fuel droplets to enable rapid evaporation and traverse rapidly through the combustion chamber [1] . There is experimental evidence to show that cavitation within injector nozzle modifies the flow characteristics of nozzle exit and favors the atomization of fuel [2][3][4][5] .Cavitation in nozzle orifice is desired to a certain degree because the collapse of cavitation bubbles influences the turbulence intensity towards the outlet of injector. Consequently, this enhances the atomization process of fuel in the combustion chamber. At the same time, the accurate prediction of cavitation zones in nozzle is quite necessary in order to avoid efficiently the erosion of the inner surface in nozzle orifice due to collapse of bubbles close to nozzle walls. However, it is usually very difficult to observe the flow state in nozzle for a real injector under operating conditions, therefore, the multidimensional numerical calculation, computational fluid dynamics (CFD) simulation, is an appropriate tool to provide a better understanding of 3D flow features inside and at the exit of injector nozzle.The Eulerian multi-fluid method introduced in this paper can be used to simulate n-phase flows and different types of injector, such as Sac-type nozzle and VCO-type nozzle. In the present work, the 3D numerical simulation of a VCO-type...

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