Variations in methane yield and microbial community profiles in the rumen of dairy cows as they pass through stages of first lactation

Considerable interest exists both from an environmental and economic perspective in reducing methane emissions from agriculture. In ruminants, CH₄ is produced by a complex community of microorganisms that is established in early life but can be influenced by external factors such as feed. Although CH₄ emissions were thought to be constant once an animal reached maturity, recent studies have shown that CH₄ yield significantly increases from early to late lactation in dairy cows. The aim of this study was to test the hypothesis that increases in CH₄ yield over the lactation cycle are related to changes in rumen microbial community structure. Nine cows were monitored throughout their first lactation cycle. Methane and dry matter intake were measured to calculate CH₄ per dry matter intake (CH₄ yield) and ruminal fluid was collected during early, mid, and late lactation. A significant difference in bacterial and archaeal community structure during early and late lactation was observed. Furthermore, when ruminal short-chain fatty acid concentrations were measured, the ratio of acetate and butyrate to propionate was significantly higher in late lactation compared with early lactation. Propionate concentrations were higher in cows with low CH₄ yield during late lactation, but no differences were observed in bacterial or archaeal community structures. Prevotella dominated the rumen of cows followed by Succinclasticum; Treponema, Fibrobacter, Ruminococcus, and Bifidobacterium were also in high abundance relative to other bacterial genera. In general, positive correlations were stronger between the most relatively abundant bacterial genera and acetate and butyrate concentrations in the cows with high CH₄ and weaker between these genera and propionate concentration. This study indicates that increased CH₄ yield in late lactation is reflected in significant changes in microbial community structure.     

Effects of pH on ex-situ biomethanation with hydrogenotrophic methanogens under thermophilic and extreme-thermophilic conditions

1. Download : Download high-res image (221KB)
2. Download : Download full-size image

     

基于高通量测序的浓香型白酒窖池古菌群落结构分析

本试验利用罗氏GS junior高通量测序平台分析了30年窖龄的浓香型白酒窖池窖泥古菌群落结构,结果发现:3口窖池样品共获得8706条有效序列,282个OTUs分类;样品中古菌的Shannon曲线值在4~5之间就趋于稳定,Chao曲线的值随着序列数的增加而增长。窖泥中古菌类群主要集中在Euryarchaeota(广古菌门)下的Thermoplasmata class(热原体纲)中的Thermoplasmataceae(热原体科),Methanobacteria class(甲烷杆菌纲)中的Methanobacteriaceae(甲烷杆菌科),Methanococci class(甲烷球菌纲)中的Methanomicrobiaceae(甲烷微菌科)、Methanocorpusculaceae(甲烷八叠球菌科)和Methanosarcinaceae(甲烷粒菌科);Saccharococcus sp.和WCHD3-02也有检测到。其中Thermoplasmataceae和Methanobacteriaceae占绝对优势,分别为39%和27%,其它菌类Methanomicrobiaceae占9%、Methanosarcinaceae占7%和Methanocorpusculaceae占4%、Saccharococcus sp.(糖球菌属)占1%和WCHD3-02占1%,unclassified序列占12%;对甲烷菌类进行深入分析,发现了Methanoculleus marisnigri strain、Methanoculleus bourgensis strain、Methanosarcina siciliae strain、Methanobacterium、Methanocorpusculum和Methanomicrobia等种属的菌种。     

丙酸质量浓度对丙酸富集培养物降解特性的影响

为阐明丙酸质量浓度对厌氧生物处理系统中丙酸降解特性的影响,研究了不同丙酸质量浓度条件下丙酸富集培养物的降解特性．以丙酸为唯一碳源,通过15代的传代培养富集到一个中温互营丙酸氧化菌群(包括丙酸氧化菌和产甲烷菌)．聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)指纹分析结果表明,该富集培养物中的丙酸氧化菌为Syntrophobacter,而嗜氢产甲烷菌和嗜乙酸产甲烷菌分别为Methanobacterium和Methanosaeta．在污泥接种量为0.81 g／L条件下,当丙酸质量浓度为1 000~2 000 mg／L时,丙酸能够被该富集培养物快速降解;而当丙酸质量浓度为2 500~3 000 mg／L时,丙酸降解和乙酸的转化均受到一定程度的抑制,但随着培养时间的延长,该抑制作用逐步解除．较高的丙酸质量浓度(≥2 500 mg／L)能够对丙酸氧化菌产生可逆性抑制作用．     

产甲烷菌高度紧密子网络分析

为了从系统水平上阐明嗜热菌的耐热机制,并指导嗜热菌在工业生产上的进一步应用,以产甲烷菌的代谢网络作为研究对象,从研究代谢网络的拓扑结构以及高度紧密子网络出发,探索常温产甲烷菌Methanosarcina acetivorans(M.acetivorans)和嗜热产甲烷菌Methanopyrus kandleri(M.kandleri)之间的代谢网络的耐热性的差异。实验结果发现常温产甲烷菌M.acetivorans最紧密的9-核和嗜热产甲烷菌M.kandleri最紧密的7-核分别包含27和19个酶。其中嗜热产甲烷菌M.kandleri网络中最紧密的7-核被分成2个子网,一个子网中的酶节点刚好是2个产甲烷菌所共同的酶,而另一个子网络中的酶是嗜热产甲烷菌M.kandleri 7-核所特有的酶,这些特有的酶全部与酪氨酸的合成有关。     

Nickel stimulation of anaerobic digestion

An acetate-enriched methanogenic culture was assayed for nutritional stimulation by nickel in combination with other inorganic and organic nutrients, i.e. iron, cobalt, yeast extract, riboflavin and vitamin B₁₂. Acetate was automatically maintained at 2–3 g l⁻¹ by a pH Stat system so that substrate was not limiting. In the absence of nickel, the specific acetate utilization rates were in the range of 2–4.6 g acetate g⁻¹ VSS day⁻¹. In the presence of nickel, this rate was as high as 10 and when both nickel and yeast extract were supplemented this rate temporarily increased to 12–15 g acetate g⁻¹ VSS day⁻¹ . The maximum acetate utilization rate was observed to be 51 g l⁻¹ day⁻¹ as compared to 3.3 g l⁻¹ day⁻¹ for conventional high-rate digestion. Daily phosphate additions were required to sustain these high acetate utilization rates. An acetate utilization rate of 20–30 g l⁻¹ day⁻¹ was maintained for over 25 days. Microscopic examination of the culture revealed a predominance of a sarcina whenever stimulation was noted.     

A comparison of media types in acetate fed expanded-bed anaerobic reactors

A synthetic feed, containing acetate as the only carbon source, was used to start-up four different anaerobic expanded-bed reactors containing three different types of microbial attachment media. The media types used were low-density anthracite, granular activated carbon (GAC) and two sizes of sand. All media types were of the same average diameter, 0.7 mm, except for a smaller sand, 0.35 mm. These media types were chosen to compare surface roughness, macroscopic shear stresses due to upflow velocity and sphericity. The 0.7 mm sand required the greatest upflow velocity, 16 cm/s, while the other reactors had upflow velocities of 5.5–6.0 cm/s. Sand had the least surface roughness and GAC had the roughest surface, while anthracite had the most angular shape. At steady-state, the GAC reactor retained 3.75–10 times the attached biomass retained on the other media tested and the GAC reactor accumulated biomass at a faster rate during start-up. Shear losses reflected the biomass accumulation with the two sand and anthracite media having shear loss coefficients 6–20 times greater than that of the GAC medium. Sand induced the formation of sludge granules in both sand reactors with two species of methanogens and stability of the sludge blankets was critical to reactor performance. Scanning electron microscopy demonstrated that attached growth developed in crevices where biomass was protected from shear forces. Attached growth on the sand and anthracite media was located only in crevices, while the GAC medium is completely covered with crevices and biofilm developed on the entire GAC particle. Surface roughness was critical to biofilm development with the rougher surface providing the better attachment medium.     

Methanogenic communities on the electrodes of bioelectrochemical reactors without membranes

Methane fermentation was successfully carried out in bioelectrochemical reactors without membranes under a working potential of − 0.6 or − 0.8 V (vs. Ag/AgCl) and neutral pH conditions. The hydrogenotrophic methanogens that dominated on the anodic and cathodic electrodes differed from those found on the electrodes in the control reactors without electrochemical reactions.     

Consecutive reaction kinetics involving a layered structure of the granule in UASB reactors

A consecutive-reaction kinetic model for the sucrose-fed upflow anaerobic sludge bed (UASB) reactor that accounts for a layered structure of the granule and the mass fraction of methanogens (f) is proposed. When the UASB reactor was maintained at the volumetric loading rates (VLR) of 7.9-13.8 kg chemical oxygen demand (COD)/m(3) d, the accumulated volatile fatty acids (VFAs) increased with increasing VLR, whereas the experimental f decreased with increasing VLR. This was primarily because methanogenesis was the rate-limiting step and the sucrose-fed granule was a layered structure. The calculated residual concentrations of sucrose and the intermediates VFAs using the layered-structure model are less deviated from the experimental measurements than those using the homogeneous-structure model. The calculated effectiveness factors for sucrose uptake and intermediates VFAs uptake (eta(1); eta(2)) ranged from 0.18 to 0.35 and 0.65 to 0.96, respectively, indicating that the overall substrate (sucrose or intermediates VFAs) removal in the UASB reactor was diffusion-controlled, especially at the VLRs of 7.9-10.6. kg COD/m(3) d. This finding was also confirmed by the simulated concentration profiles of sucrose and VFAs in the UASB-granule. From the simulation results, the effect of internal mass transfer resistance on overall substrate (sucrose) removal should not be neglected, especially for a granule size of greater than 2.0 mm.