Breakdown of Diazotized Proteins and Synthetic Substrates by Rumen Bacterial Proteases

Several different kinds of substrate were used to investigate the proteolytic activity of rumen bacteria and of proteases released from rumen bacteria by blending (“coat proteases”). These substrates included diazotized feed proteins and diazotized soluble and insoluble pure proteins. It was concluded that, while solubility was an important factor, the secondary and tertiary structure of a protein had a major influence on its rate of digestion. The resistance of elastin congo red to digestion indicated that similar fibrous proteins in plant material might resist proteolytic attack by rumen bacteria. Coat proteases had a broad specificity, including several exo- and endopeptidase activities, as determined by using synthetic peptide substrates.     

Rumen Protozoal Degradation of Structurally Intact Forage Tissues

The association with and digestion of intact leaf sections of cool- and warm-season grasses by cattle rumen protozoa were investigated by light and scanning electron microscopy and by in vitro dry matter disappearance studies. Within extensively degraded areas of mesophyll tissue in cool-season forages, almost all protozoa were Epidinium ecaudatum form caudatum, with maximum numbers at 4 to 10 h of incubation. However, few protozoa were found inside warm-season forage leaves. In in vitro dry matter disappearance studies of a series of incubations with and without 1.6 mg of streptomycin per ml, which inhibited the cellulolytic activity of the bacteria, and in comparison with uninoculated controls, rumen protozoa degraded 11.0 and 3.7 percentage units of orchardgrass and bermuda-grass, respectively. Scanning electron microscopy showed that the tissues degraded in orchardgrass consisted of large amounts of mesophyll and portions of the parenchyma bundle sheath and epidermis; no tissue loss due to the protozoa was observed in bermudagrass. The relationship of these observations to forage digestion is discussed.     

Bacterial and Protozoal Communities and Fatty Acid Profile in the Rumen of Sheep Fed a Diet Containing Added Tannins

This study evaluated the effects of tannins on ruminal biohydrogenation (BH) due to shifts in the ruminal microbial environment in sheep. Thirteen lambs (45 days of age) were assigned to two dietary treatments: seven lambs were fed a barley-based concentrate (control group) while the other six lambs received the same concentrate with supplemental quebracho tannins (9.57% of dry matter). At 122 days of age, the lambs were slaughtered, and the ruminal contents were subjected to fatty acid analysis and sampled to quantify populations of Butyrivibrio fibrisolvens, which converts C_18:2 c9-c12 (linoleic acid [LA]) to C_18:2 c9-t11 (rumenic acid [RA]) and then RA to C_18:1 t11 (vaccenic acid [VA]); we also sampled for Butyrivibrio proteoclasticus, which converts VA to C_18:0 (stearic acid [SA]). Tannins increased (P < 0.005) VA in the rumen compared to the tannin-free diet. The concentration of SA was not affected by tannins. The SA/VA ratio was lower (P < 0.005) for the tannin-fed lambs than for the controls, suggesting that the last step of the BH process was inhibited by tannins. The B. proteoclasticus population was lower (−30.6%; P < 0.1), and B. fibrisolvens and protozoan populations were higher (+107% and +56.1%, respectively; P < 0.05) in the rumen of lambs fed the tannin-supplemented diet than in controls. These results suggest that quebracho tannins altered BH by changing ruminal microbial populations.The fatty acid profile of the meat and milk of ruminants is strongly affected by diet (2, 15). When ingested, the dietary polyunsaturated fatty acids (PUFA) undergo a process known as biohydrogenation (BH) carried out by ruminal microorganisms (20). During the BH of C_18:2(n-6) (linoleic acid [LA]) and C_18:3(n-3) (linolenic acid [LNA]) a number of C_18:1 and C_18:2 isomers are formed (6). The last step in the BH process leads to the formation of C_18:0 (stearic acid [SA]). Among the intermediate products formed during this process, the isomer C_18:2 c9t11 (rumenic acid [RA]) is active in preventing cancer in mammals (17). Only a small amount of the RA found in meat and milk originates during BH. It is produced to a larger extent in muscle and mammary glands from the desaturation of C_18:1 t11 (vaccenic acid [VA], another intermediate of ruminal BH) by the action of Δ⁹-desaturase enzyme (41, 43).Ruminal BH is carried out mostly by bacteria belonging to the Butyrivibrio genus (38). Butyrivibrio fibrisolvens has the capacity to convert LA to RA and RA to VA, while Butyrivibrio proteoclasticus (previously classified as Clostridium proteoclasticum [35]) hydrogenates VA to SA (38, 39). According to Or-Rashid et al. (37), ruminal protozoa also play a role in BH by converting LA to RA. However, this issue is still controversial, as Devillard et al. (11) have reported that protozoa do not have the capability of hydrogenating LA. The proportion of BH intermediates in the rumen can vary depending on changes in ruminal microbial populations (7, 51). Changes in ruminal fatty acid profiles are also reflected in intramuscular fatty acid composition (48, 52).Tannins are phenolic compounds that are widespread in plants. When ingested by ruminants in large amounts, tannins can reduce the activity and the proliferation of ruminal microorganisms (34). Tannins from Lotus corniculatus (33) or from Acacia spp. (12) reduce the proliferation of B. proteoclasticus B316^T and B. proteoclasticus P18, respectively. Durmic et al. (12) reported that VA increased and SA decreased when extracts from Acacia iteaphylla, which contains condensed tannins (1), were incubated in vitro with sheep ruminal fluid inoculated with B. fibrisolvens JW11 and B. proteoclasticus P18 strains. In two recent in vitro studies, the inclusion of tannins in fermentor systems containing bovine ruminal fluid inhibited the conversion of VA to SA, while no effect was detected on RA production (21, 47). These results have been also confirmed in vivo in the rumen of sheep fed a diet with 4.0% dry matter (DM) quebracho tannin (48). However, to date there is no in vivo study focusing on the effects of dietary tannins on the proliferation of the microorganisms involved in ruminal BH.We assessed whether dietary tannins may affect the BH pathway via changes in bacterial and protozoal ruminal populations. We gave particular emphasis to B. fibrisolvens and B. proteoclasticus. We also assayed the production of conjugated linoleic acids (CLAs) by linoleic acid isomerase (LA-I) enzyme.     

基于18S rRNA基因的PCR/DGGE技术研究山羊瘤胃原虫动态变化

应用PCR/DGGE技术对山羊采食前后瘤胃原虫的多样性随时间的变化进行了研究.采食前和采食后1、2、4和8h分别采集瘤胃内容物样品,对瘤胃原虫特异性的18SrRNA基因经PCR扩增、DGGE电泳分析.结果显示,采食前后DGGE图谱由10条左右清晰可辨的谱带组成,图谱上的泳带反映了瘤胃内的优势原虫,泳带数量和位置的复杂性说明了瘤胃原虫的多样性.并对其中两个优势条带切胶测序,基因序列分析分属于毛口目和内毛目.瘤胃原虫区系相似性分析,采食前为90.5%～94.1%;采食后相似性发生改变,且存在个体差异.多样性指数由采食前的O.82逐渐上升到采食后8h的O.90(P>0.05).DGGE指纹技术有效地反映了不同样品中原虫优势种的组成,并可通过此技术跟踪研究瘤胃原虫区系在不同条件下的动态变化.     

Rumen Bacterial Community Transition During Adaptation to High-grain Diet

Transitional changes of the ruminal bacterial community structure in cows during the switch from roughage to high-grain diet were monitored by PCR amplification and sequencing of 16S rDNA clone libraries. In total, one hundred fifty 16S rDNA sequences of almost full-length (1.4 kb) were analysed from three libraries prepared from the rumen fluid on day 0, 3, and 28 of switch to high-grain diet. In the first library (day 0, hay diet) of 51clones, 90.2% of sequences were belonging to the low G+C Gram-positive bacteria (LGCGPB) phylum, with the minor inclusion of theCytophaga-Flavobacter-Bacteroides (CFB;3.9%), Proteobacteria (3.9%) and high G+C Gram-positive bacteria (HGCGPB;2.0%) phyla-related sequences. Six LGCGPB sequences were clustered with the well-known cellulolytics of the rumen, Ruminococcus flavefaciens and R. albus. In the second library (day 3 of high-grain diet) of 58 clones, the LGCGPB-related sequences still dominated (72.4%), albeit being represented by other species than in the first library. In particular, this library was enriched by representatives of Selenomonas-Succiniclasticum-Megasphaera group IX (17.2%), lactobacilli- (6.9%) and Butyrivibrio fibrisolvens lineage 3-related (8.6%) sequences. Other phyla were represented by CFB (22.4%) and HGCGPB (3.4%). In the third library (day 28 of high-grain diet) of 41 clones, 95% of sequences fell into the LGCGPB phylum. About half of them (46%) were clustered within theSelenomonas-Succiniclasticum-Megasphaera group in Clostridium cluster IX. No HGCGPB-related sequences were detected and CFB was represented by only a single clone. No Streptococcus bovis -related sequences were detected in any of the three clone libraries.     

Quantifying the Responses of Mixed Rumen Microbes to Excess Carbohydrate

The aim of this study was to determine if a mixed microbial community from the bovine rumen would respond to excess carbohydrate by accumulating reserve carbohydrate, energy spilling (dissipating excess ATP energy as heat), or both. Mixed microbes from the rumen were washed with N-free buffer and dosed with glucose. Total heat production was measured by calorimetry. Energy spilling was calculated as heat production not accounted by (i) endogenous metabolism (heat production before dosing glucose) and (ii) synthesis of reserve carbohydrate (heat from synthesis itself and reactions yielding ATP for it). For cells dosed with 5 mM glucose, synthesis of reserve carbohydrate and endogenous metabolism accounted for nearly all heat production (93.7%); no spilling was detected (P = 0.226). For cells dosed with 20 mM glucose, energy spilling was not detected immediately after dosing, but it became significant (P < 0.05) by approximately 30 min after dosing with glucose. Energy spilling accounted for as much as 38.7% of heat production in one incubation. Nearly all energy (97.9%) and carbon (99.9%) in glucose were recovered in reserve carbohydrate, fermentation acids, CO₂, CH₄, and heat. This full recovery indicates that products were measured completely and that spilling was not a methodological artifact. These results should aid future research aiming to mechanistically account for variation in energetic efficiency of mixed microbial communities.     

Germination and Seedling Responses of Subalpine Plants to Different Soil Substrates

In this study we explored the regeneration niche of 18 alpine plant species by testing the germination responses and seedling growth to soil mixtures made with gypsum, ophiolite, and quartzite, and a control soil. We analyzed different phases of germination: time of radicle emergence, germination duration, and germination percentage, and thereafter seedling performance measured using seedling biomasses. Species were grouped as acidophilous, basophilous and neutrophilous according to their Ellenberg indicator values. Seeds were germinated on each soil mixture in a greenhouse, and then seedlings were selected and transplanted outdoors to grow for one season at 2,050 m a.s.l. The time of radicle emergence, length of germination, final germination percentage, seedling biomass and specific leaf area (SLA) varied according to the soil mixtures depending on the pH group. There were some consistencies between the Ellenberg groups, which were built for adult plant species, and the way these seedlings responded to a particular soil mixture. For instance, the group of species predominantly occurring in basic soils during their adult life (basophilous) had the highest germination percentage and the shortest emergence time on the soil mixture composed of gypsum, but a low germination percentage and the smallest seedling biomass on the other two soil mixtures. In addition, the decrease in SLA for seedlings of the basophilous group when they were cultivated on acidic soil (especially quartzite) seems to indicate a weaker functioning of the plants. Our results highlight, first, the significance of the regeneration niche in the establishment of plants in a given soil environment, especially by emphasizing the links between germination and soil chemistry, and secondly, the consideration that different germination phases add more information about the plant community assemblage with respect to the soil environment.     

山羊瘤胃微生物宏基因组BAC文库的构建与分析

从山羊瘤胃液中提取混合微生物DNA,经BamHI部分酶切得到50kb～800kb的DNA片段后,将其连接到pCCIBAC载体上,转化E．coliEPI300,建立山羊瘤胃微生物BAC文库。经RFLP鉴定分析,该文库12672个克隆,平均插入片段为6lkb。该文库的构建为后续新型基因的筛选提供了材料,为进一步研究山羊瘤胃微生物奠定了基础。     

Macroinvertebrate Responses to Algal and Bacterial Manipulations in Streams

Our study was designed to assess the relative importance of algae and bacteria as sources of energy for stream macroinvertebrates. In one experiment, we manipulated algae by artificially shading six sections in each of two streams, one stream with an open canopy (clear-cut drainage basin) and the other with a closed canopy (forested drainage basin); both streams were in Hubbard Brook Experimental Forest, New Hampshire, USA. Chlorophyll a concentrations were reduced from 0.2 to 0.05 μg/cm² in artificially shaded sections of both streams. However, macroinvertebrates showed no response to these algal manipulations in either the clear-cut or forested stream. Nutrient concentrations (N and P) were low and limiting to primary production in both the clear-cut and forested streams. Additionally, both streams had relatively low macroinvertebrate densities suggesting bottom-up controls were important in macroinvertebrate abundance. However, the forested stream did have higher macroinvertebrate densities presumably because of higher inputs of coarse particulate organic matter from the riparian vegetation. In a second experiment, in Augusta Creek, Michigan, we manipulated both algae and bacteria. To reduce algae, we artificially shaded experimental stream channels so that chlorophyll a was reduced from natural levels of 3.0–5.6 to 0.4–0.7 μg/cm². Half of the shaded channels had dissolved organic carbon (DOC – sucrose) dripped into them to raise DOC levels by 2–3 mg/l and thus stimulate bacterial abundance. Open channels, with higher algal abundance, had higher densities of Ephemerella, but only in November when nymphs were larger. Channels with increased DOC had higher bacterial abundances, higher densities of Chironomidae and lower densities of Heptageniidae. Several other macroinvertebrate taxa that were at relatively low abundance in our samples showed no significant response to these manipulations. Our results suggest that early instar Ephemerella may not rely as heavily on algae as later instars. Also, certain taxa were able to use the heterotrophic microbial community, especially chironomids which increased in numbers when bacterial density increased; thus, the bacterial carbon source may be more important to some stream macroinvertebrates than previous studies have suggested.     

Bacterial Ingestion by the Rumen Ciliates Entodinium and Diplodinium

SYNOPSIS. In cattle fed a high-starch diet, species of Entodinium and Diplodinium ingested associated ruminal bacteria. Stained preparations of diluted rumen contents showed Entodinium caudatum, E. minimum, E. dubardi , (syn. E. simplex ), E. longinucleatum, E. bursa, E. nanellum, E. exiguum , and E. vorax contained gram-positive diplococci. Starch grains with adherent gram-positive diplococci were observed within Entodinium spp. Diplodinium ecaudatum forma ecaudatum, D. ecaudatum forma caudatum, D. neglectum and an unidentified species of Diplodinium also ingested ruminal diplococci. Bacteria were isolated from mixed species of Entodinium by washing and culturing the protozoa in a starch feed-extract agar medium. The strains isolated from the ciliates were gram-positive diplococci, 0.8 times 1–1.5 μm, which attached themselves to starch granules and were able to digest the starch. Conclusive evidence of bacterial ingestion by the oligotrichs was obtained by providing the bacterial cultures to Entodinium species ( E. dubardi and E. minimum ) which had been starved 24 hr. Gram-stained preparations showed the ciliates readily ingested the bacteria. The amylolytic cocci utilized by Entodinium spp. were identified as Streptococcus bovis.     

Conversion of C14-Labeled Substrates to Volatile Fatty Acids by the Rumen Microbiota

The fermentation of uniformly labeled glucose-C¹⁴, glucose-1-C¹⁴, -2-C¹⁴, and -6-C¹⁴, xylose-1-C¹⁴, cellulose-1-C¹⁴, -2-C¹⁴, and -6-C¹⁴, and lactate-2-C¹⁴ by rumen fluids from cows fed all-hay, hay and concentrate (50:50), and all-concentrate diets was investigated. The results obtained suggested that the Embden-Meyerhof glycolytic pathway is the major pathway of hexose utilization, that the major pathway of xylose fermentation involves hexose synthesis, and that the contributions of the nonrandomizing (acrylate) pathway of propionate formation during glucose, xylose, and cellulose fermentations are 4.5, 8.0, and 10.5%, and 24.6, 25.8, and 17.2%, respectively, by rumen fluids from the cows fed all-hay and all-concentrate rations.     

Bacterial Responses to a Simulated Colon Tumor Microenvironment

One of the few bacteria that have been consistently linked to colorectal cancer (CRC) is the opportunistic pathogen Streptococcus gallolyticus. Infections with this bacterium are generally regarded as an indicator for colonic malignancy, while the carriage rate of this bacterium in the healthy large intestine is relatively low. We speculated that the physiological changes accompanying the development of CRC might favor the colonization of this bacterium. To investigate whether colon tumor cells can support the survival of S. gallolyticus, this bacterium was grown in spent medium of malignant colonocytes to simulate the altered metabolic conditions in the CRC microenvironment. These in vitro simulations indicated that S. gallolyticus had a significant growth advantage in these spent media, which was not observed for other intestinal bacteria. Under these conditions, bacterial responses were profiled by proteome analysis and metabolic shifts were analyzed by ¹H-NMR-spectroscopy. In silico pathway analysis of the differentially expressed proteins and metabolite analysis indicated that this advantage resulted from the increased utilization of glucose, glucose derivates, and alanine. Together, these data suggest that tumor cell metabolites facilitate the survival of S. gallolyticus, favoring its local outgrowth and providing a possible explanation for the specific association of S. gallolyticus with colonic malignancy.The human intestine is the habitat for several hundred different bacterial species with an increasing bacterial concentration and variability toward the distal colon (1). The resident gut microbiota is essential for human health by making dietary nutrients available to the host and preventing the invasion of pathogens by competitive colonization and nutrient competition (2, 3). Strikingly, the part of the intestine with the highest bacterial colonization, the colon, is also most affected by cancer, with 146,970 annual cases in the United States of America (4). In a healthy colonic environment, the host has several defense mechanisms to shield itself from bacterial infection, such as the viscous mucus layer overlaying the epithelium. However, the progression of CRC¹ is accompanied by changes in the integrity of the colon, including reduced mucus production (5) and increased epithelial permeability (6). These physiological changes can drive the intestinal ecosystem, which is relatively stable during adult life, into dysbiosis (7, 8). As a consequence, the host may become more susceptible to opportunistic bacterial infections (9–11).One of the few bacteria that have been consistently linked to CRC is the opportunistic pathogen Streptococcus gallolyticus (previously known as Streptococcus bovis biotype I). In CRC patients the fecal carriage rate of this bacterium is increased from 10% to about 50% (12), which suggests that this disease facilitates the colonic survival of S. gallolyticus. Importantly, ∼60% of patients that present with S. gallolyticus endocarditis have concomitant CRC (both adenomas and carcinomas) (13, 14), which largely exceeds the rates reported in the general population (∼25%) (15). These patients had no gastro-intestinal signs or clinical symptoms of malignancy and CRC was only detected because this bacterial infection guided the physician to perform a colonoscopy.Several mechanisms for this apparent association between S. gallolyticus and CRC can be envisaged. Recently, we postulated a model in which the collagen binding ability of S. gallolyticus contributes to the specific colonization of malignant colonic sites (16). However, the altered microenvironment of the tumor may also provide conditions that favor survival and outgrowth of S. gallolyticus in this newly formed intestinal niche. For example, Hirayama et al. have shown that glucose-1-phosphate and fructose-1-phophate levels as well as amino acid concentrations were significantly higher in tumor tissue than in normal tissue (17). To investigate if this altered nutritional status of the CRC microenvironment could facilitate the foraging of S. gallolyticus, we simulated the influence of colon tumor cell metabolites on S. gallolyticus growth by incubating this bacterium in spent medium of malignant cells. Subsequently, the bacterial responses were profiled by two-dimensional proteome analysis, and metabolic shifts in the culture medium were assessed by ¹H-NMR-spectroscopy. In silico pathway analysis and further in vitro simulations showed that, unlike other intestinal bacteria, S. gallolyticus had a growth advantage under these conditions, which could mainly be attributed to increased glycolysis. These results provide the first molecular support that tumor metabolites may facilitate the local outgrowth of tumor-foraging bacteria, such as S. gallolyticus.     

Marine Bacterial Isolates Display Diverse Responses to UV-B Radiation

The molecular and biological consequences of UV-B radiation were investigated by studying five species of marine bacteria and one enteric bacterium. Laboratory cultures were exposed to an artificial UV-B source and subjected to various post-UV irradiation treatments. Significant differences in survival subsequent to UV-B radiation were observed among the isolates, as measured by culturable counts. UV-B-induced DNA photodamage was investigated by using a highly specific radioimmunoassay to measure cyclobutane pyrimidine dimers (CPDs). The CPDs determined following UV-B exposure were comparable for all of the organisms except Sphingomonas sp. strain RB2256, a facultatively oligotrophic ultramicrobacterium. This organism exhibited little DNA damage and a high level of UV-B resistance. Physiological conditioning by growth phase and starvation did not change the UV-B sensitivity of marine bacteria. The rates of photoreactivation following exposure to UV-B were investigated by using different light sources (UV-A and cool white light). The rates of photoreactivation were greatest during UV-A exposure, although diverse responses were observed. The differences in sensitivity to UV-B radiation between strains were reduced after photoreactivation. The survival and CPD data obtained for Vibrio natriegens when we used two UV-B exposure periods interrupted by a repair period (photoreactivation plus dark repair) suggested that photoadaptation could occur. Our results revealed that there are wide variations in marine bacteria in their responses to UV radiation and subsequent repair strategies, suggesting that UV-B radiation may affect the microbial community structure in surface water.     

尖叶匐灯藓对不同栽培基质的生长和生理响应北大核心CSCD

为探究不同栽培基质对尖叶匐灯藓[Plagiomnium acutum(Lindb.)T.Kop.]生长和生理指标的影响,通过实验筛选出适宜尖叶匐灯藓栽培的最优基质,为尖叶匐灯藓的繁殖栽培提供新的途径和思路。该研究以森林中常见的Ⅱ、Ⅲ、Ⅳ腐解等级的马尾松倒木(W_(Ⅱ)、W_(Ⅲ)、W_(Ⅳ))和常用的苔藓栽培土壤[颗粒土(S_(G))、通用营养土(S_(N))、草炭土(S_(C))]为栽培基质,设置6组不同基质处理,考察不同基质栽培下尖叶匐灯藓的生长长度、生长盖度、叶绿素含量、可溶性蛋白质总含量以及可溶性糖总含量,并利用Pearson相关性分析和模糊隶属函数综合评价各基质上尖叶匐灯藓总体生长状况及其影响因子。结果表明:(1)各栽培基质间的理化性质存在显著差异,倒木基质(W_(Ⅱ)、W_(Ⅲ)和W_(Ⅳ))的总孔隙度、持水能力以及全氮含量显著高于S_(G)和S_(N)基质,而S_(G)和S_(N)基质的容重、全磷含量和全钾含量显著高于倒木基质;SC基质除总孔隙度和持水孔隙与倒木基质有显著差异外,其他指标均较为接近。(2)6组不同栽培基质中,倒木基质(W_(Ⅱ)、W_(Ⅲ)、W_(Ⅳ))可以更有效提高尖叶匐灯藓配子体生长长度和生长盖度,S_(C)基质可以提高尖叶匐灯藓叶绿素含量,提升其光合能力,S_(G)基质栽培可以提升可溶性糖和可溶性蛋白质含量,进而增强其植物抗性;W_(Ⅳ)基质上尖叶匐灯藓的隶属函数综合评价得分最高,综合生长状况最好。(3)基质的总孔隙度、持水孔隙、持水能力和全氮含量与尖叶匐灯藓的生长形态指标呈极显著正相关关系;而基质的容重、全磷含量、全钾含量与苔藓的生长形态指标呈极显著负相关关系。研究认为,倒木基质相比于土壤基质具有较大的孔隙度和持水能力,更有利于尖叶匐灯藓的生长,并以腐解Ⅳ级的马尾松倒木基质中尖叶匐灯藓综合生长发育状况最好,可以作为栽培尖叶匐灯藓最优基质;在尖叶匐灯藓的生产栽培中适当增大基质的孔隙度、持水能力和全氮含量将有利于其生长。     

The Bacterial Flora of the Rumen of Healthy and Bloating Calves

Rumen samples from five healthy milk-fed calves and one healthy calf given a milk-replacer diet containing yeast protein had pH values of 6.5–8.0, total counts of ca. 10¹⁰/ml and viable counts of 10⁸-10¹⁰/ml. The facultatively and strictly anaerobic, and obligately aerobic, components of the floras were enumerated and identified. Similar tests performed on samples from two calves bloating on the yeast diet had pH values of 4.8 and 5.3, and although total and viable counts were of the same order as those from healthy calves, obligately aerobic bacteria were not detected and counts of lactobacilli were elevated. Infusion of the rumen of a calf with yeast diet caused a reduction in pH from 7.3–5.1 and an increase of at least 100-fold in the numbers of organisms capable of forming copious gas from yeast diet. Results suggest that milk or milk-replacer diet normally does not enter the rumen to any extent but when it does, due perhaps to poor palatability, bloat may ensue.     

Comparison of Substrate Affinities Among Several Rumen Bacteria: a Possible Determinant of Rumen Bacterial Competition

Five rumen bacteria, Selenomonas ruminantium, Bacteroides ruminicola, Megasphaera elsdenii, Streptococcus bovis, and Butyrivibrio fibrisolvens were grown in continuous culture. Estimates of substrate affinities were derived from Lineweaver-Burk plots of dilution rate versus substrate concentration. Each bacterium was grown on at least four of the six substrates: glucose, maltose, sucrose, cellobiose, xylose, and lactate. Wide variations in substrate affinities were seen among the substrates utilized by a species and among species for the same substrate. These wide differences indicate that substrate affinity may be a significant determinant of bacterial competition in the rumen where soluble substrate concentrations are often low. Growth of these bacteria in continuous culture did not always follow typical Michaelis-Menten kinetics. Inflated theoretical maximum growth rates and non-linear Lineweaver-Burk plots were sometimes seen. Maintenance energy expenditures and limitation of growth rate by factors other than substrate concentration (i.e., protein synthesis) are discussed as possible determinants of these deviations.     

Bacterial Infection Disrupts Clock Gene Expression to Attenuate Immune Responses

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Rumen Bacterial Diversity of 80 to 110-Day-Old Goats Using 16S rRNA Sequencing

The ability of rumen microorganisms to use fibrous plant matter plays an important role in ruminant animals; however, little information about rumen colonization by microbial populations after weaning has been reported. In this study, high-throughput sequencing was used to investigate the establishment of this microbial population in 80 to 110-day-old goats. Illumina sequencing of goat rumen samples yielded 101,356,610 nucleotides that were assembled into 256,868 reads with an average read length of 394 nucleotides. Taxonomic analysis of metagenomic reads indicated that the predominant phyla were distinct at different growth stages. The phyla Firmicutes and Synergistetes were predominant in samples taken from 80 to 100-day-old goats, but Bacteroidetes and Firmicutes became the most abundant phyla in samples from 110-day-old animals. There was a remarkable variation in the microbial populations with age; Firmicutes and Synergistetes decreased after weaning, but Bacteroidetes and Proteobacteria increased from 80 to 110 day of age. These findings suggested that colonization of the rumen by microorganisms is related to their function in the rumen digestive system. These results give a better understanding of the role of rumen microbes and the establishment of the microbial population, which help to maintain the host’s health and improve animal performance.