Novel Saccharomyces cerevisiae Culture: Effects on Performance, Muscle Quality and Intestinal Microorganisms of Fattening Pig

Zheng Wenyong, Yang Tao, Li Shuangquan, Lv Changxu, Shi Min, Ma Libao, Yan Xianghua

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Chinese Agricultural Science Bulletin ›› 2020, Vol. 36 ›› Issue (21) : 145-154. DOI: 10.11924/j.issn.1000-6850.casb20190600268

Novel Saccharomyces cerevisiae Culture: Effects on Performance, Muscle Quality and Intestinal Microorganisms of Fattening Pig

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Abstract

The purpose is to investigate the effects of the addition of new S. cerevisiae culture (YCB) in the diet on the performance, muscle quality and intestinal microbes of fattening pigs. 440 healthy three-way hybrid (Duroc × Landrace × Yorkshine) fattening pigs with an initial body weight of (61.49±0.36 kg) were randomly divided into 4 groups. The basal diet with no S. cerevisiae culture was test group I, adding 2.5% traditional yeast culture (YCA) was test group II, adding 2.5% new yeast culture (YCB) was test group III, and adding 5% YCB was test group IV. The test period was 60 days. The results showed that: (1) the addition of YCA and YCB in the basic diet improved the average daily gain and feed utilization rate of the fattening pigs, and the feed-weight ratio of the test IV group was the lowest, but no significant difference was shown (P >0.05); (2) compared with the test group I, the muscle drip loss rate and shear force in the test group II, III and IV were significantly reduced (P<0.05), and they were the lowest in the test group IV; compared with the test group I, the intramuscular fat in the test group II, III and IV increased by 2.8%, 6.7%, and 6.9%, respectively, but the differences were not significant; transmission electron microscopy revealed that the fibrillin protein in the test group II and IV was slightly degraded, and the myofibrillar proteins in the test group I and III were significantly degraded; (3) the abundance of genus Fibrinolytics such as Ruminococcus, Treponema, and Staphylococcus was increased in the feces of group III and IV, and lipid metabolism, carbohydrate metabolism, starch and sucrose metabolism were significantly enhanced (P<0.05), to improve bile acid metabolism and lipid metabolism. In summary, the addition of YCB to the fattening pig production can improve the performance and muscle quality of the fattening pigs. By regulating the intestinal microbes and then affecting the body metabolism, the suitable addition amount in the production is 5%.

Key words

novel Saccharomyces cerevisiae culture / fattening pig / production performance / muscle quality / intestinal microbes

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Zheng Wenyong , Yang Tao , Li Shuangquan , Lv Changxu , Shi Min , Ma Libao , Yan Xianghua. Novel Saccharomyces cerevisiae Culture: Effects on Performance, Muscle Quality and Intestinal Microorganisms of Fattening Pig. Chinese Agricultural Science Bulletin. 2020, 36(21): 145-154 https://doi.org/10.11924/j.issn.1000-6850.casb20190600268

0 引言

土壤冻融作用是指在中、高纬度或高海拔及部分温带地区由于气温的变化[1],导致土壤热量也随之变化进而引起土壤水分发生相变,土壤出现反复“结冻—融化”过程,土体收缩或膨胀交替[2],引起土壤结构被破坏和性状发生改变的过程[3]。冻融过程在影响土壤水热条件变化的同时[4,5],还通过影响土壤理化性质、微生物活性发生变化[6],进而影响土壤养分循环与利用[7]。1960年后国际上已陆续展开对于冻土带和季节冻土区土壤冻融生态效应的研究[8]。然而,中国的相关研究相对较晚,对于土壤冻融格局改变对土壤生态效应影响的研究仍十分有限[1,9-10]
氮素是生物体构成的重要元素、是植物生长发育必需的营养元素之一,也是最易消耗和植物生长的限制元素之一[11]。土壤中氮素主要以有机态氮和无机态氮两大类存在,氮总量的95%以上为有机氮,植物根系可直接吸收利用小部分可溶性有机氮,但多数情况下,只有无机氮才能被植物有效吸收利用[12,13]。有机氮与无机氮在土壤中的相互转化即为土壤氮素的转化过程,其转化过程受诸多人为和自然因素干扰,有研究指出冻融作用对于土壤氮素循环起着调控因子作用[14],是土壤氮素循环的主要驱动力,因此冻融格局(冻融频数、结冻持续时间以及结冻强度)的改变对于氮转化均有较大影响。

1 冻融作用对土壤氮矿化的影响

氮矿化过程是氮转化的起始过程,是土壤氮素在微生物的作用下由有机态转化为无机态的过程,对土壤氮素迁移转化以及氮素的生物地球化学循环具有重要意义[13]。全球变暖现象日渐加剧,土壤温度随着大气温度的变化而有所改变。冻融频数、冻结持续时间、冻结强度等冻融格局的改变对中、高纬度或高海拔地区土壤氮素转化过程有何影响也已逐渐成为研究的焦点问题[11,15]

1.1 冻融频数对土壤氮矿化的影响

周幼吾等[16]根据冻融持续周期将土壤状态分为短时冻土、季节性冻土以及隔年冻土、多年冻土。蔡延江等[11]在对去除雪被越冬期原位采样试验中,研究发现,3个月的冻结持续时间对氮矿化速率无明显影响,而结冻持续4~5个月时氮矿化速率显著增加,说明长时间的冻结有利于土壤氮矿化。在较长时间尺度上冻融频次的变化对氮矿化有着强烈的影响[17]。贾国晶等[18]通过对长白山森林土壤的研究发现,在经过35次冻融循环后,相比一次冻融土壤无机氮质量分数在多次冻融后显著提高。土壤中无机氮质量分数随着冻融次数的增加而增加,高频的冻融循环促进了无机氮在土壤中的积累[19]。这与Sulkava等[20]研究结果相似。Amador等[21]研究发现在第一次冻融时,土壤净氮矿化速率比较快,但随着冻融频数的增加净矿化速率逐渐降低,表明较少的冻融循环次数有利于土壤氮的矿化。其原因主要为:(1)同干湿交替或氯仿熏蒸处理结果类似,矿质氮直接来自于土壤微生物细胞破裂的释放[22];(2)部分死亡微生物的残体为余下的微生物活动提供了充足的碳源,激发了微生物活性,有利于土壤有机氮的矿化过程[19];(3)冻融交替使土壤孔隙扩张与收缩交替,最终引起土壤晶格构造发生改变,释放出被固定的铵态氮[23,24]
Hentschel等[25]研究表明,土壤氮矿化速率随着冻融循环频数的增多而增强。而Herrmann[19]在40天内将农田土壤进行了20次冻融循环,发现随着冻融频次的增加,土壤氮矿化速率逐渐下降。胡霞等[26]在苔原生态系统、森林生态系统中也得到了类似的研究结果。净氮矿化速率随冻融频数的增加而减弱可能是由两方面原因导致的:一是较野外原位试验相比,室内的模拟试验涵盖因素尚不全面,缺少植物根系对氮素的吸收利用以及降水导致氮素的淋溶损失,氮矿化速率被土壤中大量积累的矿化氮所抑制[18,21]。此外,冻融作用下部分微生物死亡生物量减少,微生物活性下降,同样会影响氮矿化速率[20]。从而干扰了冻融作用对氮矿化影响效应的长期分析。

1.2 冻融强度对土壤氮矿化的影响

周旺明等[27]通过对湿地土壤氮和氮矿化的研究表明,-5~5℃冻融温差处理的土壤矿化氮累积量低于-25~5℃处理,这与Deluca的研究结果一致[28]。Groffman等[22]和Neilsen等[29]则发现相对较高的冻结温度对土壤氮矿化无影响,冰冻温度为-13℃时氮矿化增强;Larsen等[30]发现氮矿化量在冻结温度为-4~2℃时明显低于未冻结和永久冻结处理。所以重度冻结状态下的土壤产生的氮矿化累积量高于轻度冻结,氮矿化量随着冻融交替的温差波动幅度增加而升高,极端的冷冻温度会增加土壤氮的矿化作用[31]
冻融格局的改变可以对土壤氮的矿化作用产生积极的影响,近期研究表明,冻融频数的增加、冻融强度的增大以及持续时间的增强,均有利于土壤无机氮质量分数的增多和氮矿化速率的加快,但胡霞等[26]在研究中得出了不同结论。因此在研究冻融作用对于土壤氮矿化的影响时,不仅要从氮矿化作用的本身生物学过程考虑[11],还应综合土壤性质,植物类型以及植物根系吸收,土壤微生物状况等环境因素进行分析。

2 冻融作用对硝化作用与无机氮流失的影响

硝化作用是指在好氧环境下,铵离子在硝化微生物作用下转化为亚硝酸盐或硝酸盐的过程。降水淋溶过程是陆地生态系统氮循环过程中无机氮与可溶性有机氮迁移和损失的重要途径[32]

2.1 冻融频数对硝化作用与无机氮流失的影响

宋长春等[33]在对沼泽湿地季节性冻融期CO2、CH4和N2O排放研究时发现,在较高循环次数下可溶性氮组分中仅NH4+-N含量显著增加,而NO3--N含量明显降低。出现这种现象的可能原因是:高频次的土壤冻融循环使土壤水分由液相变为固相,被固定在土壤孔隙中,使土壤中氧气含量减少,土壤处于嫌气状态,好氧微生物活性被抑制,厌氧微生物活性增强,硝化过程被削弱而反硝化过程被促进[34],所以,NO3--N的含量减少了。而且反硝化细菌对低温的耐受程度强于硝化细菌[35,36],只要温度升高土壤开始处于解冻融化状态,反硝化功能就会迅速恢复。因此,在高频数的冻融循环条件下,NO3--N的消耗量增加,冻融循环对硝化过程的促进作用就会被反硝化过程掩盖。
殷睿等[37]研究表明,浅雪被森林土壤在频繁的冻融循环作用下,土壤氮淋溶损失以NO3--N为主,其次为可溶性有机氮、再次为NH4+-N。NO3--N淋溶量高于NH4+-N淋溶量的原因在于带正电荷的NH4+-N易附着于带负电荷的土壤胶体上,而带负电荷的NO3--N更易淋失,故NO3--N淋溶量较高[38,39],因此冬季土壤较强的硝化作用所导致的NO3--N含量的增加也是淋溶液中NO3--N含量高的重要原因。

2.2 冻融持续时间对硝化作用与无机氮流失的影响

徐俊俊等[40]研究发现随着冻融时间的增加,可溶性有机氮、NH4+-N 和NO3--N含量呈先增加后下降的趋势。李源等[23]研究发现4天的短期冻融循环使硝化速率和矿化速率降低,氨化速率提高,NH4+-N含量有所提高。而138天的长期自然冻融提高了矿化速率和氨化速率,在土壤水含量较高时,长时间的反硝化和淋溶作用抑制了硝化作用发生,使NO3--N含量显著降低,NH4+-N含量明显提高。土壤处于长期冻结情况下,土壤中存留的NH4+-N、NO3--N含量均会升高,而剧烈的冻融条件会使这部分氮素的流失加剧[41]

2.3 冻融强度对硝化作用与无机氮流失的影响

冻融强度的波动必将影响到土壤中氮素的矿化和硝化作用[23,39],有研究表明-10℃的弱冻有利于NO3--N含量增加,使NH4+-N含量降低,-20℃强冻使NO3--N增加量显著大于NH4+-N减少量。当温度在10℃以下时,土壤中的氨化速率通常高于硝化速率[42]。强冻可能不是通过促进NO3--N的生成量来增加土壤的矿化作用,而是通过减少NH4+-N的转移量。在内蒙古草原地区土壤冻融过程中氮素矿化的研究发现,与冻结前相比,土壤融化后NH4+-N总量降低了56%,NO3--N总量增加了84%[43]。低温结冻处理后,云杉林和枫榉树林土壤NH4+-N含量均显著提高[44]
不同冻融格局因素的改变对土壤硝化作用影响都不尽相同,随着冻融频数与冻融持续时间的增加,土壤NO3--N含量趋于降低更易淋失;而随着冻融强度的加剧,土壤NO3--N的含量趋于增加。当然土壤中NO3--N含量的改变量不一定能真实的反映出土壤硝化作用的变化,因此,如何明确在冻融过程NO3--N中含量的变化与土壤硝化作用的关系应需进一步研究讨论。

3 冻融作用对反硝化作用与N2O排放的影响

反硝化作用则是指在嫌气环境下,硝酸盐或亚硝酸盐在反硝化微生物作用下被还原为气态NO、N2O和N2的过程[11]。N2O是一种存留时间长、可进入平流层,并引起臭氧的损耗的温室气体。目前多数研究认为冻融循环中反硝化作用是N2O产生的主要途径[1],土壤理化性质、有机质含量、微生物活性以及冻融格局等影响土壤反硝化过程的因素都会影响N2O排放[45]

3.1 冻融频数对反硝化作用与N2O排放的影响

冻融会使N2O气体大量逸出,冻融作用会破坏土壤团粒结构并释放大量营养物质,随着冻融频数增加,微生物虽逐渐适应频繁的冻融交替环境,但其可利用的有机底物和营养物质含量逐渐下降,微生物活性会呈先增强后减弱的规律,所以N2O排放量一般呈先增加后减少的趋势[46,47]。Papen等[48]和Wu等[49]在野外观测研究中发现,当气温缓慢动态上升至0℃以上时,N2O的排放仅小幅增加,而当冻融循环次数增加或温度波动上升明显时,N2O的排放会出现显著的峰值。由此可见,在野外自然条件下,在第一次冻融循环过程中一般不会形成土壤N2O的排放高峰,而是在冻融循环频数增加或温度显著升高时产生。在第一次冻融循环过程中,由于土壤水分的体积增大使土壤孔隙扩张,土壤晶格被破坏其固定的营养元素和一些活性有机物质的释放供微生物利用,从而可以促进矿化和反硝化作用的发生[50]。但多次冻融循环之后N2O的产生与排放量随着土壤本底碳、氮含量及有效性的逐渐降低而减少。

3.2 冻融持续时间对反硝化作用与N2O排放的影响

有研究发现,冻结11天的土壤N2O排放量比冻结3天的土壤N2O排放量要多22%[51],很可能是冰层的存在阻碍了下层土壤N2O的排放并造成累积,所以融化后N2O释放量急剧升高。Luo等[52]通过对德国森林土壤N2O排放动态监测发现,在15年中仅在其中年均土壤温度较低以及冻结期持续约3~4周较长的5年发现全年的N2O排放显著受融循环影响。这与Teepe和Ludwig的模拟试验结果相似,冻结持续时间越长,N2O的排放量越大[53]

3.3 冻融强度对反硝化作用与N2O排放的影响

徐星凯等[54]研究发现-18℃和-80℃冻结处理后冻土融化N2O排放脉冲峰值显著高于-8℃冻结处理,严重冻结后土壤NH4+-N释放量的增加可以刺激硝化作用,使得随后的反硝化作用也随之增强进而引起N2O排放量的增加;Koponen的研究结果表明,冻融交替期间土壤N2O气体的排放量在冻结温度为-15℃时远高于-1.5℃处理下土壤的N2O排放量[55]
冻融格局的改变均促进了土壤反硝化过程提高了N2O排放量,因此我们在有效地确定影响冻融作用对N2O排放机制的主导因素方面仍有很大的挑战。

4 结语与展望

作为普遍存在于中、高纬度或高海拔地区的非生物应力,冻融作用通过改变土壤的水热条件进而影响土壤的理化性质,影响土壤元素的养分循环[54]。氮素作为植物生长发育必需的限制元素之一,土壤冻融作用明显影响其转化过程。本研究从冻融格局改变的角度总结了目前关于冻融作用对于氮转化研究的一般性规律:随着冻融格局的改变,均有利于土壤氮的矿化;冻融强度的增加可显著提高土壤硝态氮的含量;冻融格局的改变也会提高N2O的排放。
目前为止关于冻融作用对于氮转化过程机理研究并不全面。由于15N同位素示踪法、乙炔抑制法等方法的局限性,仅通过测定土壤无机氮的改变量并不能真实反映冻融作用下土壤氮转化的动态特征[11]。冻融作用对于氮素转化的研究室内模拟实验多于野外原位观察,但这其中存在许多局限性。例如:(1)实验土壤脱离原土体,温度变化脱离实际情况,室内实验冻融循环温差大且变化迅速;然而,自然状态下土壤冻融极端温度不会太低且变化缓慢;(2)室内模拟实验一般忽略了在土壤融化时期氮素的径流损失等因素;(3)研究采样地点多集中于中、高纬度地区,而高海拔地区研究相对较少[56,57]
当前,冻融作用对于氮转化作用机理研究尚有不足,得出结论并不全面,对于室内模拟实验与野外原位观察所得出的有关土壤氮转化特征的异同尚不明确,相关研究亟待加强。

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In summary, published research data clearly show that the use of antibiotics during all phases of growth benefits the rate and efficiency of body weight gain, reduces mortality and morbidity, reduces subclinical disease, and improves health in pigs. Also, antibiotics at breeding and during lactation benefits reproductive and lactational performance in sows. The economic benefits are several-fold greater than the cost of the antibiotic when a cost-effective antibiotic is used for this purpose. Monitoring and surveillance of microbial resistance in animals and humans has continued, with no animal-to-human infection path being clearly delineated. Although the incidence of antibiotic resistance in the human population remains high, there is no clear evidence that the levels or patterns have changed. The high levels of antimicrobial resistance in humans likely result from antibiotics prescribed directly to humans, because well over half of the antibiotics produced in the United States is used in human medicine. Whether antibiotic usage in swine, poultry, and other food-producing animals contributes to antibiotic resistance in the human population will continue to be debated. Even though antibiotics have been fed for nearly 50 years to literally billions of animals, there is still no convincing evidence of unfavorable health effects in humans that can be directly linked to the feeding of subtherapeutic levels of antibiotics to swine or other animals. Hopefully, policy decisions in the future regarding the use of antimicrobials in animals will be based on science and sound risk assessment, and not on emotionalism.
[3]
Chen T, Cheng G, Ahmed S, et al. New methodologies in screening of antibiotic residues in animal-derived foods: biosensors[J]. Talanta, 2017,175:435-442.
Antibiotics are leading medicine asset for fighting against microbial infection, but also one of the important causes of death worldwide. Many antibiotics used as therapeutics and growth promotion agents in animals can lead to antibiotic residues in animal-derived food which harm the health of people. Hence, it is vital to screen antibiotic residues in animal derived foods. Typical methods for screening antibiotic residues are based on microbiological growth inhibition and immunological analyses. However these two methods have some disadvantages, such as poor sensitive, lack of specificity and etc. Therefore, it is necessary to develop simple, more efficient and high sensitive screening methods of antibiotic residues. These assays have been introduced for the screening of numerous food samples. Biosensors are emerging methods, applied in screening antibiotic residues in animal-derived foods. Two types of biosensors, whole-cell based biosensors and surface plasmon resonance-based sensors have been extensively used. Their advantages include portability, small sample requirement, high sensitivity and good specificity over the traditional screening methods.
[4]
Li G, Lillehoj H S, Lee K W, et al. Immunopathology and cytokine responses in commercial broiler chickens with gangrenous dermatitis[J]. Avian Pathology, 2010,39(4):255-264.
Gangrenous dermatitis (GD) is an emerging disease of increasing economic importance in poultry resulting from infection by Clostridium septicum and Clostridium perfringens type A. Lack of a reproducible disease model has been a major obstacle in understanding the immunopathology of GD. To gain better understanding of host-pathogen interactions in GD infection, we evaluated various immune parameters in two groups of birds from a recent commercial outbreak of GD, the first showing typical disease signs and pathological lesions (GD-like birds) and the second lacking clinical signs (GD-free birds). Our results revealed that GD-like birds showed: reduced T-cell and B-cell mitogen-stimulated lymphoproliferation; higher levels of serum nitric oxide and alpha-1-acid glycoprotein; greater numbers of K55(+), K1(+), CD8(+), and MHC class II(+) intradermal lymphocytes, and increased K55(+), K1(+), CD8(+), TCR1(+), TCR2(+), Bu1(+), and MHC class II(+) intestinal intraepithelial lymphocytes; and increased levels of mRNAs encoding proinflammatory cytokines and chemokines in skin compared with GD-free chickens. These results provide the first evidence of altered systemic and local (skin and intestine) immune responses in GD pathogenesis in chickens.
[5]
龙凌. 酵母产品及其用途[J]. 中国饲料, 2001: 28-30.
[6]
Fathi M M, Almansour S, Alhomidan A, et al. Effect of yeast culture supplementation on carcass yield and humoral immune response of broiler chicks[J]. Veterinary World, 2012,5:651.
[7]
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[8]
Peetschwering C M C V D, Jansman A J M, Smidt H, et al. Effects of yeast culture on performance, gut integrity, and blood cell composition of weanling pigs[J]. Journal of Animal Science, 2007,85(11):3099.
[9]
Wensheng T. Effects of yeast culture on gut microbial composition and activity of growing-fattening pigs in summer[J]. Journal of Nanjing Agricultural University, 2013,36(4):91-98.
[10]
贺琴, 王自蕊, 游金明, 等. 基于MiSeq高通量测序方法研究酵母壁多糖对断奶仔猪盲肠菌群结构的影响[J]. 中国畜牧杂志, 2017,53(9):125-131.
[11]
郜亮亮, 刘玉满, 潘春玲. 中国居民猪肉消费特征及其变迁分析[J]. 中国畜牧业, 2015(20):41-43.
[12]
陈娟, 吕常旭, 李双全, 等. 高温环境下酵母培养物对育肥猪生长性能及肉品质的影响[J]. 饲料博览, 2017(7).
[13]
高慧兰, 侯鹏霞, 梅宁安, 等. 日粮中添加酿酒酵母培养物对肉牛生产性能及经济效益的影响[J]. 畜牧与饲料科学, 2017(7).
[14]
Geng Ch, Yin R L, Ping Z, et al. Comparison of active dry yeast (Saccharomyces cerevisiae) and yeast culture for growth performance, carcass traits, meat quality and blood indexes in finishing bulls[J]. Animal Science Journal, 2016,87(8).
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Watanabe A, Daly C C, Devine C E. The effects of the ultimate pH of meat on tenderness changes during ageing[J]. Meat Science, 1996,42(1):70-78.
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姚仕彬, 叶元土, 蔡春芳, 等. 酵母培养物水溶物对丙二醛损伤的离体草鱼肠道黏膜细胞的保护作用[J]. 动物营养学报, 2014,26(9).
[18]
Muroya S, Ertbjerg P, Pomponio L, et al. Desmin and troponin T are degraded faster in type IIb muscle fibers than in type I fibers during postmortem aging of porcine muscle[J]. Meat Science, 2010,86(3):764-769.

Abstract

A novel approach was applied in this study to directly evaluate the effect of muscle fiber type on postmortem protein degradation. Porcine muscle fibers were isolated from longissimus muscle at day 1, 3, and 6 postmortem. Fibers were sorted by immunochemical myosin heavy chain isoform typing. Western blot analysis of fibers pooled separately into type I or IIb showed that the relative amounts of 39- and 50-kDa desmin degradation fragments at day 6, and 28- to 31-kDa fragments of troponin T fast type isoform (fTnT) at day 1 and 6 postmortem were higher in type IIb than in type I fibers. At day 6 troponin T slow type isoform (sTnT) was less degraded than fTnT in type I fibers. These results indicated greater rate and extent of proteolysis in type IIb than in type I fibers and higher susceptibility of fTnT to proteolysis than that of sTnT isoform.

[19]
梁婷玉, 吴建平, 刘婷, 等. 肌纤维类型分类及转化机理研究进展[J]. 肉类研究, 2018,32(09):65-71.
[20]
Kim H B, Isaacson R E. The pig gut microbial diversity: Understanding the pig gut microbial ecology through the next generation high throughput sequencing[J]. Veterinary Microbiology, 2015,177(3-4):242-251.
The importance of the gut microbiota of animals is widely acknowledged because of its pivotal roles in the health and well being of animals. The genetic diversity of the gut microbiota contributes to the overall development and metabolic needs of the animal, and provides the host with many beneficial functions including production of volatile fatty acids, re-cycling of bile salts, production of vitamin K, cellulose digestion, and development of immune system. Thus the intestinal microbiota of animals has been the subject of study for many decades. Although most of the older studies have used culture dependent methods, the recent advent of high throughput sequencing of 16S rRNA genes has facilitated in depth studies exploring microbial populations and their dynamics in the animal gut. These culture independent DNA based studies generate large amounts of data and as a result contribute to a more detailed understanding of the microbiota dynamics in the gut and the ecology of the microbial populations. Of equal importance, is being able to identify and quantify microbes that are difficult to grow or that have not been grown in the laboratory. Interpreting the data obtained from this type of study requires using basic principles of microbial diversity to understand importance of the composition of microbial populations. In this review, we summarize the literature on culture independent studies of the pig gut microbiota with an emphasis on its succession and alterations caused by diverse factors.
[21]
Kallus S, Brandt L J. The Intestinal Microbiota and Obesity[J]. Journal of Clinical Gastroenterology, 2012,46(1):16-24.
[22]
Purslow, Peter P. Contribution of collagen and connective tissue to cooked meat toughness; some paradigms reviewed[J]. Meat Science, 2018:S0309174018300482.
[23]
Blaut M, Klaus S. Intestinal Microbiota and Obesity[J]. Handbook of experimental pharmacology, 2012,209(209):251-273.
[24]
Schwiertz A, Taras D, SchFer K, et al. Microbiota and SCFA in Lean and Overweight Healthy Subjects[J]. Obesity, 2009,18(1):190-195.
Obesity has recently been linked to the composition of human microbiota and the production of short chain fatty acids (SCFAs). However, these findings rely on experimental studies carried out using rather small and defined groups of volunteers or model animals. Our aim was to evaluate differences within the human intestinal microbiota and fecal SCFA concentration of lean and obese subjects. A total of 98 subjects volunteered to take part in this study. The BMI in kg/m(2) of 30 volunteers was within the lean range, 35 were overweight and 33 were obese. The fecal microbiota was characterized by real-time PCR analyses. With the primers used herein we were able to cover 82.3% (interquartile range of 68.3-91.4%) of the total microbiota detectable with a universal primer. In addition, the concentration of SCFA was evaluated. The total amount of SCFA was higher in the obese subject group (P = 0.024) than in the lean subject group. The proportion of individual SCFA changed in favor of propionate in overweight (P = 0.019) and obese subjects (P = 0.028). The most abundant bacterial groups in faeces of lean and obese subjects belonged to the phyla Firmicutes and Bacteroidetes. The ratio of Firmicutes to Bacteroidetes changed in favor of the Bacteroidetes in overweight (P = 0.001) and obese subjects (P = 0.005). Our results are in line with previous reports suggesting that SCFA metabolism might play a considerable role in obesity. However, our results contradict previous reports with regard to the contribution of various bacterial groups to the development of obesity and this issue remains controversial.
[25]
Xia L, Dai L, Yu Q, et al. Persistent Transmissible Gastroenteritis Virus Infection Enhances Enterotoxigenic Escherichia coli K88 Adhesion by Promoting Epithelial-Mesenchymal Transition in Intestinal Epithelial Cells[J]. J. Virol., 2017,91(21).
HIV-1 poorly infects monocyte-derived dendritic cells (MDDCs). This is in large part due to SAMHD1, which restricts viral reverse transcription. Pseudotyping HIV-1 with vesicular stomatitis virus G protein (VSV-G) strongly enhances infection, suggesting that earlier steps of viral replication, including fusion, are also inefficient in MDDCs. The site of HIV-1 fusion remains controversial and may depend on the cell type, with reports indicating that it occurs at the plasma membrane or, conversely, in an endocytic compartment. Here, we examined the pathways of HIV-1 entry in MDDCs. Using a combination of temperature shift and fusion inhibitors, we show that HIV-1 fusion mainly occurs at the cell surface. We then asked whether surface levels or intracellular localization of CD4 modulates HIV-1 entry. Increasing CD4 levels strongly enhanced fusion and infection with various HIV-1 isolates, including reference and transmitted/founder strains, but not with BaL, which uses low CD4 levels for entry. Overexpressing coreceptors did not facilitate viral infection. To further study the localization of fusion events, we generated CD4 mutants carrying heterologous cytoplasmic tails (LAMP1 or Toll-like receptor 7 [TLR7]) to redirect the molecule to intracellular compartments. The intracellular CD4 mutants did not facilitate HIV-1 fusion and replication in MDDCs. Fusion of an HIV-2 isolate with MDDCs was also enhanced by increasing surface CD4 levels. Our results demonstrate that MDDCs are inefficiently infected by various HIV-1 and HIV-2 strains, in part because of low CD4 levels. In these cells, viral fusion occurs mainly at the surface, and probably not after internalization.IMPORTANCE Dendritic cells (DCs) are professional antigen-presenting cells inducing innate and adaptive immune responses. DCs express the HIV receptor CD4 and are potential target cells for HIV. There is debate about the sensitivity of DCs to productive HIV-1 and HIV-2 infection. The fusion step of the viral replication cycle is inefficient in DCs, and the underlying mechanisms are poorly characterized. We show that increasing the levels of CD4 at the plasma membrane allows more HIV fusion and productive infection in DCs. We further demonstrate that HIV fusion occurs mainly at the cell surface and not in an intracellular compartment. Our results help us understand why DCs are poorly sensitive to HIV infection.
[26]
付殿国, 徐明. 微生态制剂[J]. 吉林畜牧兽医, 2005(4):13-15.
微生态学是联邦德国VoekerRusch博士1977年首先提出的概念,何明清教授将其描述为"研究正常微生物与其宿主内环境相互依赖和相互制约机制的细胞水平及分子水平生态科学州"[1].微生态制剂则是根据微生态学的微生态平衡、微生态失调、微生态营养和微生态防治等理论,利用正常微生物群成员或其促进物质制成的能够调整机体微生态平衡的活的微生物制剂,因此又称为益生素或促生素.由于微生态制剂能够在数量或种类上补充肠道内所缺乏的正常微生物,可以调整或维持肠道内微生态平衡,增强免疫功能,促进营养物质的消化吸收,从而达到无病防病,有病治病,提高饲料转化率和畜禽生产性能的作用.因此,这一学科一经提出,便得到了广大生命科学工作者的足够重视,取得了迅速发展.

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Copyright reserved © 2020. Chinese Agricultural Association Bulletin. All articles published represent the opinions of the authors, and do not reflect the official policy of the Chinese Agricultural Association or the Editorial Board, unless this is clearly specified.
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