Methane emission,digestive characteristics and faecal archaeol in heifers fed diets based on silage from brown midrib maize as compared to conventional maize

The aim of the present experiment was to compare silage prepared from maize having a brown midrib (BMR) mutation with control (CTR) maize to identify their effects on enteric methane emission, digesta mean retention time (MRT), ruminal fermentation and digestibility. In addition, the utility of archaeol present in faecal samples was validated as a proxy for methane production. Seven German Holstein heifers were fed total mixed rations with a maize-silage proportion (either BMR or CTR) of 920 g/kg dry matter (DM) in a change-over design. Heifers were fed boluses with markers to measure MRT; faeces were collected for 7 days and rumen fluid was collected on the penultimate day. Methane emission was measured in respiration chambers on one day. Data were analysed by t-test and regression analysis. DM intake did not differ between the two diets. The apparent digestibility of DM and most nutrients was unaffected by diet type, but apparent digestibility of neutral and acid detergent-fibre was higher in those heifers fed BMR than in those fed CTR. Comparisons between diets revealed no difference in particle or solute MRT in the gastro-intestinal tract and the reticulorumen. Concentrations of short-chain fatty acid and ammonia in rumen fluid and its pH were not affected by silage type. Independent of the mode of expression [l/d, l/kg DM intake, l/kg digested organic matter], methane emissions were not affected by maize-silage type, but with BMR, there was a trend towards lower methane production per unit of digested neutral detergent fibre than there was with CTR silage. Results of the present study show that feeding heifers BMR silage does not increase methane emissions despite a higher fibre digestibility as compared to CTR silage. Therefore, it is assumed that improvements in animal productivity achieved by feeding BMR silage, as some studies have reported, can be obtained without extra environmental cost per unit of milk or meat. Neither faecal archaeol content [µg/g] nor daily amount excreted [mg/d] is suitable to predict methane production in absolute terms [l per day]. However, faecal archaeol content has a certain potential for predicting the methane yield [l per kg DM intake] of individual animals.     

玉米雄穗性状遗传结构与形成分子机制*

玉米为雌雄同株异花植物,其雄穗着生于植株顶部,雌穗腋生。雄穗一方面需产生足量花粉以保证雌穗授粉结实,另一方面由于对下部叶片的遮蔽作用和自身营养需求,其生长发育会同时影响叶片光合作用效率和能量分配,因此优化雄穗结构是提高玉米产量的重要措施之一。玉米雄穗性状包括雄穗分枝数、雄穗分枝长度、雄穗主轴长度、雄穗分枝总长度、雄穗分枝角度等,均为多基因控制的数量性状。自20世纪90年代,研究者开始利用数量性状位点(quantitative trait locus,QTL)定位方法解析玉米雄穗性状遗传结构;随着玉米自交系B73等参考基因组释放,以及DNA微阵列、基因组重测序等高通量基因分型技术的日益成熟,全基因组关联分析(genome-wide association study, GWAS)成为数量性状遗传研究的主流方法,目前已鉴定出大量玉米雄穗性状遗传位点。通过总结雄穗性状遗传定位研究结果,构建一致性图谱并挖掘定位热点区间,有助于进一步了解雄穗性状遗传结构特征及指导雄穗性状候选基因克隆。此外,通过对调控雄穗发育的已知基因进行功能分类,可为解析玉米雄穗发育的遗传网络和调控通路提供理论支撑。     

Effects of lanthanum on rumen fermentation, urinary excretion of purine derivatives and digestibility in steers

The objective of this study was to evaluate the effects of LaCl₃ supplementation on rumen fermentation, urinary excretion of purine derivatives and feed digestibility in the total tract of steers. Eight ruminally cannulated Simmental steers (420 ± 20 kg) were used in a replicated 4 × 4 Latin square experiment. The treatments were control (without LaCl₃); La-low; La-medium and La-high with 450, 900 and 1800 mg LaCl₃ per steer per day, respectively. Diet consisted of 600 g/kg corn stover and 400 g/kg concentrate (dry matter [DM] basis). Dry matter intake (averaged 9 kg/day) was restricted to a maximum of 90% of ad libitum intake. Ruminal pH (range of 6.59–6.42) was quadratically (P<0.04) changed, whereas total volatile fatty acids (VFA) concentration (range of 74.16–88.61 mM) was linearly (P<0.01) and quadratically (P<0.01) increased with increasing La supplementation. Ratio of acetate to propionate decreased linearly (P<0.01) from 3.28 to 1.79 as La supplementation increased due to the increased in propionate production. In situ ruminal neutral detergent fibre (aNDF) degradation of corn stover was improved but the crude protein (CP) degradability of soybean meal was decreased with increasing La supplementation. Urinary excretion of purine derivatives was quadratically (P<0.01) changed with altering La supplementation (75.5, 81.0, 82.4 and 70.6 mmol/day for control, low-, medium- and high-LaCl₃ supplementation, respectively). Similarly, digestibilities of organic matter, aNDF and CP in the total tract were also linearly and quadratically increased with increasing La supplementation. The present results indicate that supplementation of diet with LaCl₃ improved rumen fermentation and feed digestion in beef cattle. It was suggested that the La stimulated the digestive microorganisms or enzymes in a dose-dependent manner. In the experimental conditions of this trial, the optimum La dose was about 900 mg LaCl₃ per steer per day.     

Engineering a native homoethanol pathway in Escherichia coli B for ethanol production

A native homoethanol pathway (pyruvate-to-acetyl-CoA-to-acetaldehyde-to-ethanol) was engineered in Escherichia coli B. The competing fermentation pathways were eliminated by chromosomal deletions of the genes encoding for fumarate reductase (frdABCD), lactate dehydrogenase (ldhA), acetate kinase (ackA), and pyruvate formate lyase (pflB). For redox balance and anaerobic cell growth, the pyruvate dehydrogenase complex (aceEF-lpd, a typical aerobically-expressed operon) was highly expressed anaerobically using a native anaerobic inducible promoter. The resulting strain SZ420 (ΔfrdBC ΔldhA ΔackA ΔfocA-pflB ΔpdhR::pflBp6-pflBrbs-aceEF-lpd) contains no foreign genes and/or promoters and efficiently ferments glucose and xylose into ethanol with a yield of 90% under anaerobic conditions.     

Study of beta-glucosidase production by wine-related yeasts during alcoholic fermentation. A new rapid fluorimetric method to determine enzymatic activity

AIMS: The beta-glucosidase activity is involved in the hydrolysis of several important compounds for the development of varietal wine flavour. The aim of the present study was to investigate the production of beta-glucosidase in a number of wine-related yeast strains and to measure and identify this activity over the course of grape juice fermentation. METHODS AND RESULTS: beta-glucosidase activity was measured as the amount of 4-methylumbelliferone released from 4-methylumbelliferyl-beta-d-glucopyranoside substrate. Intact cells of some grape and wine-spoilage yeasts showed beta-glucosidase activity much higher than those observed in wine yeasts "sensu stricto". During fermentation, three Saccharomyces cerevisiae strains, one Hanseniaspora valbyensis strain and one Brettanomyces anomalus strain showed beta-glucosidase activity both intra- and extracellularly. CONCLUSIONS: In the studied strains, beta-glucosidase activity was at its maximum when the cells were in the active growth phase. However, a lowering of medium pH to values around 3 during fermentation led to total loss of activity. SIGNIFICANCE AND IMPACT OF THE STUDY: During the course of this study, a new, rapid and reproducible method to assay beta-glucosidase activity was developed. The fact that Saccharomyces and non-Saccharomyces yeast strains are able to express beta-glucosidase activity during the alcoholic fermentation sheds new light on the contribution of these yeasts in the aroma expression of wines.     

Modification by glucose of the flocculent phenotype of a <Emphasis Type="Italic">Kloeckera apiculata</Emphasis> wine strain

We have evaluated the induction of the flocculent phenotype of Kloeckera apiculata by glucose mc1 and propose a pathway involved in carbohydrate flocculation induction. Pulses of glucose were given to cells growing in glucose-poor medium (2 g l(-1)) and the flocculation percentage was measured. To elucidate the mechanism involved in flocculation induction, cycloheximide was injected into the cultures 120 min before the glucose pulse. 2,4-Dinitrophenol or cAMP was added to the media instead, or simultaneously with glucose, while a protein kinase A (PKA) inhibitor was added 30 min before the glucose pulse. With 20 and 50 g l(-1) glucose pulse, the yeast flocculation percentage arises to 55 and 65%, respectively. The quantity of proteins and the reflocculating capacity of a lectinic protein extract from the yeast cell wall increase as the concentration of glucose pulse was higher. Cycloheximide prevented the glucose-induced flocculation, while cAMP or 2,4-dinitrophenol increased it 4- and 5-fold, respectively. PKA inhibitor completely prevented the glucose induction flocculation. The flocculent phenotype of K. apiculata mc1 was induced by glucose and the mechanism seems to imply de novo protein (lectin) synthesis via the PKA transduction pathway. This work contributes to the elucidation of the mechanism involved in flocculation induction by glucose of a non-Saccharomyces wine yeast, K. apiculata, which has not been reported. The induction of flocculation by glucose could be a biotechnological tool for the early removal of the indigenous microorganisms from the grape must before the inoculation of a selected starter strain to conduct the alcohol fermentation.     

红树内生海洋细菌CIII-1发酵条件初步研究

摇瓶法测定结果表明,用7号培养基,初始pH 7.5,装液量1/10摇瓶体积,转速150 r/min,温度25℃下培养96 h,菌株分泌产生抗番茄青枯病细菌的物质最多,抑菌圈直径最大,为红树植物内生海洋细菌CIII-1菌株产抗植物青枯病菌物质的最佳培养条件。并发现该菌株产生的抗菌物质对西瓜枯萎病菌、香蕉枯萎病菌等植物病原真菌也有较强的拮抗作用。