Sole Carbohydrate Source Research Articles

Effect of silica on the colonization of rice straw by ruminal bacteria

The relationship between silica distribution and microbial colonization in the cuticle of rice straw was examined using scanning electron microscopy and energy dispersive X-ray microanalysis (EDX). Rice straw stems cut into 1 -cm lengths were either treated with 40 g NH3 kg−1 dry matter (DM) or left untreated. Microbial colonization was examined using cultures of Fibrobacter succinogenes S85 grown on rice straw as the sole source of carbohydrate. The nylon bag technique was also used to study the colonization of rice straw by mixed ruminal microorganisms and to determine in sacco dry matter disappearance (ISDMD). Examination by EDX revealed the outer (abaxial) surface of the leaf sheath to be virtually covered by silica, with high levels of accumulation within distinctly arranged opaline bodies (phytoliths). Silica was distributed diffusely over most of the inner (adaxial) surface of the leaf sheath, but phytoliths were absent and some regions were devoid of silica. Ammonia treatment dramatically increased the ISDMD of rice straw, but did not alter the content or distribution of silica on either surface of the leaf sheath. Trichomes contained no silica and were major sites of invasion and colonization in the intact cuticle of rice straw. Cuticular damage and loss were more prevalent in treated than in untreated rice straw, and underlying tissues were found to be devoid of silica and extensively colonized. The improved digestibility of ammonia-treated rice straw may be partially due to a weakening of the adhesion between the cuticle and underlying tissues. Detachment of the cuticle removes this barrier to digestion and exposes underlying silica-free tissues to bacterial colonization.

Evaluation of alternative nitrogen and carbon sources for sugarbeet suspension culture platings in development of cell selection schemes

Low molecular weight nitrogenous impurity compounds as well as raffinose are negative quality factors that interfere with efficient processing of sugarbeet (Beta vulgaris L.) for sucrose. In order to identify nutrient media for cell selection of biochemical mutants or transgenics that might have reduced levels of these processing impurities, the ability of 10 endogenous compounds to serve as sole nitrogen or carbon source for suspension plating and subculture callus growth was evaluated. The most productive concentrations of nitrate, ammonium, l-glutamine, l-glutamate, urea, and l-proline as sole nitrogen sources supported plating callus growth at 106, 159, 233, 167, 80, and 52%, respectively, as well as the historical 60 mM mix of nitrate and ammonium in Murashige-Skoog medium. Glycine betaine and choline did not support growth. d(+) Raffinose and d(+) galactose supported plating callus growth only 67 and 25%, respectively, as well as sucrose as sole carbohydrate source. No callus growth occurred on glutamine, glutamate, or glycine betaine as the sole carbon or carbon plus nitrogen source. Platings on either nitrate or ammonium as sole nitrogen source did not differ in sensitivity to the nitrate uptake inhibitor phenylglyoxal, suggesting that phenylglyoxal lacks the specificity for use in selection for mutants of nitrate uptake. The ability of raffinose to be used as the carbon source, and glutamine or glutamate as the nitrogen source, may preclude their use for selection of genetic variants accumulating less of these processing impurities. However, mutants or transgenics able to utilize either glutamine, glutamate, or glycine betaine might be selectable on media containing any one of these as carbon, nitrogen, or carbon plus nitrogen source, respectively, that is incapable of supporting wild-type cell growth.

Influence of fructose and glucose on the production of exopolysaccharides and the activities of enzymes involved in the sugar metabolism and the synthesis of sugar nucleotides in Lactobacillus delbrueckii subsp. bulgaricus NCFB 2772

The effect of fructose and glucose on the growth, production of exopolysaccharides and the activities of enzymes involved in the synthesis of sugar nucleotides in Lactobacillus delbrueckii subsp. bulgaricus grown in continuous culture was investigated. When grown on fructose, the strain produced 25 mg l-1 exopolysaccharide composed of glucose and galactose in the ratio 1:2.4. When the carbohydrate source was switched to a mixture of fructose and glucose, the exopolysaccharide production increased to 80 mg l-1, while the sugar composition of the exopolysaccharide changed to glucose, galactose and rhamnose in a ratio of 1:7.0:0.8. A switch to glucose as the sole carbohydrate source had no further effect. Analysis of the enzymes involved in the synthesis of sugar nucleotides indicates that in cell-free extracts of glucose-grown cells the activity of UDP-glucose pyrophosphorylase was higher than that in cell-free extracts of fructose-grown cells. The activities of dTDP-glucose pyrophosphorylase and the rhamnose synthetic enzyme system were very low in glucose-grown cultures but could not be detected in fructose-grown cultures. Cells grown on a mixture of fructose and glucose showed similar enzyme activities as cells grown on glucose. Analysis of the intracellular level of sugar nucleotides in glucose-grown cultures of L. delbrueckii subsp. bulgaricus showed the presence of UDP-glucose and UDP-galactose in a ratio of 3.3:1, respectively, a similar ratio and slightly lower concentrations were found in fructose-grown cultures. The lower production of exopolysaccharides in cultures grown on fructose may be caused by the more complex pathway involved in the synthesis of sugar nucleotides. The absence of activities of enzymes leading to the synthesis of rhamnose nucleotides in fructose-grown cultures appeared to result in the absence of rhamnose monomer in the exopolysaccharides produced on fructose.

Dietary Carbohydrate Type and Fat Amount Alter VLDL and LDL Metabolism in Guinea Pigs

The effects of low/high fat diets and simple/complex carbohydrate intake on specific aspects of plasma VLDL and LDL metabolism were evaluated. Guinea pigs were fed for 4 wk two different fat/carbohydrate concentrations: 2.5/58 (g/100 g) or 25/29 (g/100 g) with either sucrose or cornstarch as the sole carbohydrate source. Intake of high fat diets resulted in higher plasma cholesterol (P < 0.001), whereas sucrose intake resulted in higher plasma triacyglycerol (TAG) concentrations (P < 0.03). Intake of starch increased apolipoprotein (apo) B secretion rates (P < 0.001), and nascent VLDL were smaller and contained less TAG/apo B than particles from the sucrose-fed group (P < 0.01). Guinea pigs fed the starch diets had higher plasma VLDL apo B flux and faster VLDL apo B clearance than those fed sucrose diets (P < 0.01). In addition, more rapid VLDL removal from plasma in guinea pigs fed complex carbohydrate/high fat diets was associated with less conversion of VLDL to LDL and lower plasma cholesterol concentrations compared with the high fat/sucrose group (P < 0.01). Low fat compared with high fat intake resulted in 60% more rapid plasma LDL apo B fractional catabolic rates (FCR). The LDL apo B fractional catabolic rate of all dietary groups was inversely correlated with plasma cholesterol concentrations (r = -0.83, P < 0.001). These results demonstrate that in guinea pigs, low fat diets decrease plasma LDL cholesterol concentrations by increasing LDL turnover rates, and complex carbohydrates reduce plasma TAG by affecting the composition of nascent VLDL particles and by increasing VLDL apo B catabolism.

Dietary fat amount and carbohydrate type regulate hepatic acyl CoA:cholesterol acyltransferase (ACAT) activity. Possible links between ACAT activity and plasma cholesterol levels

The effects of dietary fat amount and carbohydrate type were evaluated on hepatic acyl CoA:cholesterol acyltransferase (ACAT) activity in guinea pigs to determine whether there was a correlation between plasma LDL cholesterol concentrations induced by diet and rates of hepatic cholesterol esterification. Animals were fed two different fat:carbohydrate ratios: 2.5:58% ( w w ) (low fat) or 25:29% ( w w ) (high fat) with either sucrose or starch as the sole carbohydrate source. Fat contributed 6.9 and 53% of total calories respectively. Consumption of high fat diets resulted in higher plasma cholesterol concentrations (P < 0.001) while simple carbohydrate intake increased plasma triacylglycerol levels (P < 0.01). Animals fed the high fat:sucrose diet exhibited the highest plasma and hepatic cholesterol concentrations. The type of carbohydrate affected the distribution of hepatic cholesterol pools in that animals fed sucrose had higher concentrations of free while those fed starch had higher levels of esterified cholesterol (P < 0.01). Hepatic ACAT activity was up-regulated in animals fed high fat diets (P < 0.01) with no effect due to carbohydrate type. A significant correlation was found between hepatic ACAT activity and plasma LDL cholesterol concentrations (r = 0.69, P < 0.001) and between hepatic ACAT activity and cholesterol influx to the liver (r = 0.97, P < 0.01). These results demonstrate that modifications in hepatic ACAT activity induced by dietary factors could be a response to the influx of cholesterol to the liver or could be related to the rates of incorporation of cholesteryl ester into lipoproteins secreted by the liver.

In Vitro Fructooligosaccharide Utilization and Inhibition of Salmonella spp. by Selected Bacteria

In vitro experiments were conducted to determine: 1) inhibitory capacities of potential direct-fed microbial bacteria against Salmonella serotypes; and 2) the ability of Bifidobacterium bifidum, Enterococcus faecium, Lactobacillus casei, Lactococcus lactis, Pediococcus sp., and Salmonella spp. to grow in media containing fructooligosaccharides (FOS-50® or FOS pure formulation) as the only carbohydrate source. Thirteen bacteria (two strains of Bacillus coagulans, Bacillus licheniformis, Bacillus subtilis, B. bifidum, faecium, two strains of Lactobacillus acidophilus, L. casei, Pediococcus sp Propionibacterium acidopropionici, P. jensenii, and Propionibacterium sp.) tested for inhibition of six Salmonella serotypes (S. California, S. enteritidis, heidelberg, S. mission, S. senftenberg, and S. typhimurium) using a spot-the-technique. Bifidobacterium bifidum, E. faecium, all lactobacilli, and Pediococcus sp. clearly inhibited growth of all Salmonella serotypes. In the growth experiments, E. faecium, L. lactis, and Pediococcus sp. grew in media with either FOS-50® or the pure formulation of FOS as the sole carbohydrate source. All tested Salmonella serotypes utilized FOS-50® for growth; however growth varied among the serotypes. In contrast, none of the Salmonella serotypes grew in media containing the pure formulation of FOS as the only carbohydrate source.

An intraluminal model of necrotizing enterocolitis in the developing neonatal piglet

The most common risk factors for the development of necrotizing enterocolitis (NEC) are prematurity and enteral feeding. Most models of NEC involve ischemic insult resulting in generalized necrosis, different from the classical ileocecal predilection of NEC. This anatomic predisposition is explained by dysmotility of immature gut, leading to bacterial overgrowth in the terminal ileum and colon. Infant formula containing lactose as the sole carbohydrate source overwhelms partially developed lactase activity, allowing enteric bacteria to ferment excess carbohydrate to shortchain fatty acids, decreasing intraluminal gut pH and predisposing to mucosal injury. Impaired clearance of intraluminal contents exacerbates this effect. In the present study the authors used a model of NEC, originally developed in rabbits and based on analysis of intestinal contents of NEC babies, modified and adapted here to neonatal piglets, the gastrointestinal tract of which more closely resembles the human neonate. Method: Piglets <3 days old and 2 weeks old were laparotomized. Loops created from the distal ileum to the proximal colon were injected with isoosmolar acidified casein solution or 0.9% saline. Segments were harvested 3 hours later, sectioned for H&E, and graded from 0 (intact villi) to 4 (transmural necrosis). Results: Acidified casein-induced damage included areas of necrosis, submucosal edema, inflammatory cell infiltrate, and lymphatic distension. In younger animals, lesions were more pronounced (3.25 ± 0.13 for the <3-day-old v 2.43 ± 0.14 for the 2-week-old piglets; P < .005). Conclusion: The authors believe that this piglet NEC model most closely approximates human NEC because it incorporates two of the most common risk factors: dysmotility (by creating intestinal loops) and enteral feeding (by intraluminal injection of acidified casein).

Production of specific glycosidase activities by Streptococcus intermedius strain UNS35 grown in the presence of mucin

An isolate of Streptococcus intermedius from a brain abscess showed neuraminidase (sialidase), beta-D-galactosidase, N-acetyl-beta-D-glucosaminidase and N-acetyl-beta-D-galactosaminidase activities. The optimal pH values of these enzymes were 5.5-6.0, 5.5-6.0, 5.0-5.5 and 5.0-5.5, respectively. The km of the enzymes varied according to whether the type of substrate was chromogenic or fluorogenic; sialidase was most active at the lowest substrate concentrations, with a km of 0.01 mM. In semi-defined medium, with porcine gastric mucin--a model glycoprotein--as the sole source of fermentable carbohydrate, levels of the glycosidases were significantly increased. Addition of glucose to the mucin-containing medium, or growth of cells in media supplemented with glucose alone, repressed glycosidic activities and the majority of these were cell-associated. S. intermedius cells from cultures grown with mucin were able, simultaneously, to transport via sugar:phosphoenolpyruvate phosphotransferase (PTS) systems, monosaccharides which are constituents of carbohydrate side chains of glycoproteins. These cells also possessed significant levels of neuraminate-pyruvate lyase, involved in the intracellular catabolism of neuraminic acid; this was absent from cells grown with glucose. These mechanisms, collectively, may facilitate the persistence and growth of S. intermedius in vivo.

Effect of low-fat colostrum on fat accretion and lipogenic enzyme activities in adipose tissue in the 1-day-old pig

Fat accretion, body fatty acid (FA) composition and adipose tissue lipogenic enzyme activities were determined in 1-day-old piglets fed during the first day of life sow colostrum that was either normal (control) or low in fat and high in lactose, galactose or glucose as the sole source of carbohydrate. Malic enzyme activity did not change during the first postnatal day while increases ( P < 0.01) were found for glucose-6-phosphate dehydrogenase and acetyl-CoA-carboxylase. However, fat accretion was closely dependent on the amount of ingested fat and FA composition of piglets indicates a shift towards that of colostrum, the extent of which was dependent on the amount of ingested fat. Plasma glucose and insulin levels were the highest ( P < 0.01) in piglets fed the colostrum high in glucose and plasma free fatty acid (FFA) levels were the lowest ( P < 0.01) in piglets fed the low-fat, high-carbohydrate colostra. Liver weight and glycogen concentration were higher ( P < 0.01) in piglets fed the colostra low in fat and high in carbohydrate than in those on the control colostrum. It is suggested that synthesis of fatty acids from carbohydrate is negligible in the newborn pig even in the presence of high plasma insulin and low plasma FFA levels. The metabolic fate of carbohydrate is discussed.

Requirements for biotin are not affected by the combination of copper deficiency and fructose feeding.

The objective of the present study was to establish whether copper (Cu)-deficient rats fed a diet containing fructose as their sole carbohydrate source require more biotin than the recommended 2 mg/kg diet when egg-white serves as the dietary protein. Eighty weanling male Sprague-Dawley rats were randomly divided into 8 groups according to type of dietary carbohydrate (starch or fructose), level of Cu (0.6 micrograms Cu/g diet or 6.0 micrograms Cu/g diet) and level of biotin (2 mg/kg diet or 10 mg/kg diet). Regardless of the level of dietary biotin, Cu-deficient rats fed a fructose-containing diet exhibited growth retardation, anemia, atrophied pancreata, enlarged hearts and similar death rates. The remaining Cu-deficient rats fed fructose were emaciated and sick regardless of dietary biotin levels. The concentration of biotin in serum and biotin content of liver of rats fed fructose were higher than corresponding values from rats fed starch. Cu-deficient rats fed fructose are not deficient in biotin compared to published normal values. Supplementation of 10 mg/biotin/kg diet did not improve morbidity or mortality and therefore was not beneficial.

Enhanced production of α‐amylase in fed‐batch cultures of Bacillus subtilis TN106[pAT5

Growth of Bacillus subtilis TN106[pAT5] and synthesis of plasmid-encoded protein (alpha-amylase) are investigated in batch, continuous, and fed-batch cultures using a defined medium containing glucose and/or starch as the carbohydrate source. The batch culture studies reveal that reduced availability of arginine hampers growth of recombinant cells (which lack an arginine synthesis gene) but promotes production of alpha-amylase and substitution of glucose by starch as the carbohydrate source leads to slower growth of recombinant cells and increased production of alpha-amylase per unit cell mass. Retention of recombinant cells over prolonged periods in continuous cultures is not possible without continuous application of antibiotic selection pressure owing to segregational plasmid instability. Fed-batch experiments with constant volumetric feed rate demonstrate that alpha-amylase production is enhanced at lower feed concentration of starch (sole carbohydrate source) and lower volumetric feed rate. Such slow addition of starch is however not conducive for growth of recombinant cells. The expression of the thermostable alpha-amylase gene carried on the recombinant plasmid pAT5 (derived from a plasmid isolated from a thermophilic bacterium) is promoted at higher temperatures, while growth of recombinant cells is depressed. In all batch and fed-batch experiments, production of alpha-amylase is observed to be inversely related to growth of recombinant cells. The efficacy of two-stage bioreactor operations, with growth of recombinant cells being promoted in the first stage and alpha-amylase production in the second stage, in attaining increased bulk alpha-amylase activity is demonstrated.

Inability of Lactobacillus plantarum and other lactic acid bacteria to grow on D‐ribose as sole source of fermentable carbohydrate

Lactobacillusplantarum NCIMB 8026, NCIMB 8026(s), NCIMB 8014, NCFB 1752, Lact. brevis NCIMB 4617, Leuconostoc mesenteroides NCIMB 8023, Streptococcus agalactiae NCFB 1348, Pediococcus acidilactici NCFB 1859 and Ped. pentosaceus NCFB 990 did not grow on D‐ribose as the sole source of fermentable carbohydrate in a chemically defined medium but grew on D‐ribose in the presence of glucose. Lactobacillus plantarum NCIMB 8026(s) also grew on D‐xylose and L‐arabinose in the presence but not in the absence of glucose. Enterococcus faecalis NCFB 581 grew with D‐ribose as the sole fermentable carbohydrate. Leuconostoc mesenteroides NCIMB 8710 and Lactococcus lactis subsp. lactis NCFB 763 did not use ribose in the presence or absence of glucose. Lactobacillus plantarum NCIMB 8026(s) utilized ribose and glucose simultaneously in the proportion of approximately 1 ribose to 1 glucose, producing approximately 3 lactate to 1 acetate and similar yields of dry biomass from glucose and ribose. Growth of Lact. plantarum 8026(s) with glucose and excess D‐ribose ceased when D‐glucose was exhausted, but metabolism of D‐ribose to lactic and acetic acids continued. The enzyme system for the metabolism of D‐ribose in Lact. plantarum was inducible, requiring D‐glucose and amino acids for adaptation.

Research Note: Fructose Feeding Increases Lower Gut Weights in Germ-Free and Conventional Chicks

The present study was conducted to investigate whether there was any effect of carbohydrate sources on the magnitude of differences in growth and tissue weights found between germ-free and conventional environments in the chicken. Germ-free and conventional birds were allowed free access to a purified diet in which glucose or fructose was used as a sole carbohydrate source from 7 to 17 days of age. Growth performance and visceral weights were measured at the end of the experiment. The results indicated that there was no difference in growth, feed intake, or feed efficiency between the two environments, but that feeding fructose increased feed intake and decreased feed efficiency compared with feeding glucose. The conventional birds had heavier visceral organ weights including liver, jejuno-ileum, and cecum than did the germ-free counterparts. Feeding fructose resulted in lighter liver weight and heavier weights of jejuno-ileum and cecum than feeding glucose. It was concluded that consuming fructose might increase the lower gut weight of the chicken, as was found by the association with normal microflora, but might not affect overall growth compared with consuming glucose.

Characterization of wall‐bound invertase isoforms of Picea abies cells and regulation by ectomycorrhizal fungi

In culture, the ectomycorrhiza‐forming fungi Amanita muscaria (Pers. ex Fries) Hock. and Hebeloma crustuliniforme (Bull. ex Fries) Quel. only grow on media with glucose or fructose but not with sucrose as sole carbohydrate source. This is due to their lack of wall‐bound invertase activity. Therefore, utilization of sucrose by the fungi within a mycorrhizal association is believed to depend on the wall‐bound invertase activity of the host. This enzyme activity was studied in the apoplast of suspension cultured cells of Picea abies (L.) Karst. An ionically and a tightly wall‐bound isoform of acid invertase were found that function as β‐d‐fructofuranoside‐fructohydrolases (EC 3.2.1.26). The ionically bound enzyme could be easily released from walls of intact cells with buffer of high ionic strength. In its native form, the ionically bound invertase isoform is a monomeric protein with a molecular mass of 61 kDa, as determined by gel filtration and SDS‐PAGE. Glycoprotein nature of the enzyme was demonstrated with antibodies directed against the digoxigenin‐labeled protein. The Km values of both enzymes for sucrose, their natural substrate, are relatively high (ionically bound invertase Km= 16 mM, tightly bound invertase Km= 8.6 mM). Activity of both wall‐bound invertase isoforms strongly depends on the apoplastic pH. They have a narrow pH‐optimum and exhibit highest activity at pH 4.5. with elevated activity between pH 4.5 and 6.0. Furthermore, fructose acts as competitive inhibitor of both isoforms, whereas glucose is not inhibitory. Unloading of sucrose from host cells to the apoplastic interface of the Hartig net in ectomycorrhizae appears to depend on the rate of hydrolysis by the wall‐bound invertase of the host. Since the activity of the plant invertase depends on the actual pH value and the fructose concentration in the mycorrhizal interface, we suggest that the fungus can actively influence the activity of the plant invertase by acidification of the cell wall and by fructose uptake. Thus, the fungus itself can regulate its own supply of glucose and fructose.

Effect of dietary carbohydrate and phenotype on sucrase, maltase, lactase, and alkaline phosphatase specific activity in SHR/N-cp rat.

The obese spontaneous hypertensive rat/NIH-corpulent (SHR/N-cp) rat exhibits some of the metabolic and pathologic alterations associated with non-insulin-dependent diabetes mellitus and hypertension. The current study was conducted to investigate the influence of phenotype (ob versus In) and source of dietary carbohydrate (sucrose versus starch) on intestinal sucrase, maltase, lactase, and alkaline phosphatase activity in SHR/N-cp rats. For 3 months, lean and obese male SHR/N-cp rats were fed isocaloric diets containing as the sole source of carbohydrate either 54% cooked corn starch or sucrose. Serum and urine markers for diabetes were observed in obese rats. Wet weight and length of intestines were significantly increased in obese rats compared with lean littermates. Among the intestinal enzymes measured, statistical tests confirmed that sucrase activity was significantly increased (P < 0.01) by both phenotype (ob > In) and feeding a sucrose diet. Diet alone (sucrose > starch) significantly increased (P < 0.05) maltase activity in obese rats, but had no effect on lean rats. Lactase activity was significantly higher (P < 0.05) in obese sucrose-fed rats compared with obese starch-fed and/or lean littermates. Statistical tests revealed that intestinal alkaline phosphatase activity was significantly altered (P < 0.05) by both phenotype and diet. Intestinal alkaline phosphatase was higher in starch-fed lean rats compared with lean littermates fed sucrose and to starch or sucrose-fed obese rats. These results are not indicative of a simple, nonspecific increase in intestinal enzyme activity, since the effects observed in intestinal alkaline phosphatase contrast the effects observed in intestinal sucrase, maltase, and lactase activity. These results indicate that both phenotype and diet alter structural and enzymatic intestinal activities of SHR/N-cp rats. Distinct variations in the observed intestinal enzymatic activities suggest that these enzymes are under the control of genetic, hormonal, and dietary factors. Rationale for these differences are discussed.

Genetic analysis of a locus on the Bacteroides ovatus chromosome which contains xylan utilization genes.

Bacteroides ovatus, a gram-negative obligate anaerobe found in the human colon, can utilize xylan as a sole source of carbohydrate. Previously, a 3.8-kbp segment of B. ovatus chromosomal DNA, which contained genes encoding a xylanase (xylI) and a bifunctional xylosidase-arabinosidase (xsa), was cloned, and expression of the two genes was studied in Escherichia coli (T. Whitehead and R. Hespell, J. Bacteriol. 172:2408-2412, 1990). In the present study, we have used segments of the cloned region to construct insertional disruptions in the B. ovatus chromosomal locus containing these two genes. Analysis of these insertional mutants demonstrated that (i) xylI and xsa are probably part of the same operon, with xylI upstream of xsa, (ii) the true B. ovatus promoter was not cloned on the 3.5-kbp DNA fragment which expressed xylanase and xylosidase in E. coli, (iii) there is at least one gene upstream of xylI which could encode an arabinosidase, and (iv) xylosidase rather than xylanase may be a rate-limiting step in xylan utilization. Insertional mutations in the xylI-xsa locus reduced the rate of growth on xylan, but the concentration of residual sugars at the end of growth was the same as that with the wild type. Thus, a slower rate of growth on xylan was not accompanied by less extensive digestion of xylan. Mutants in which xylI had been disrupted still expressed some xylanase activity. This second activity was associated with membranes and produced xylose from xylan, whereas the xylI gene product partitioned primarily with the soluble fraction and produced xylobiose from xylan.

Enzymes associated with metabolism of xylose and other pentoses by Prevotella (Bacteroides) ruminicola strains, Selenomonas ruminantium D, and Fibrobacter succinogenes S85.

Prevotella (Bacteroides) ruminicola strains B(1)4 and S23 and Selenomonas ruminantium strain D used xylose as the sole source of carbohydrate for growth, whereas Fibrobacter succinogenes was unable to metabolize xylose. Prevotella ruminicola strain B(1)4 exhibited transport activity for xylose. In contrast, F. succinogenes lacked typical xylose uptake activity but did exhibit low binding potential for the sugar. Prevotella ruminicola strains B(1)4 and S23 as well as S. ruminantium D showed low xylose isomerase activities but higher xylulokinase activities, using assays that gave high activities for these enzymes in Escherichia coli. Xylose isomerase appeared to be produced constitutively in these ruminal bacteria, but xylulokinase was induced to varying degrees with xylose as the source of carbohydrate. Fibrobacter succinogenes lacked xylose isomerase and xylulokinase. All three species of ruminal bacteria possessed transketolase, xylulose-5-phosphate epimerase, and ribose-5-phosphate isomerase activities. Neither P. ruminicola B(1)4 nor F. succinogenes S85 showed significant phosphoketolase activity. The data indicate that F. succinogenes is unable to either actively uptake or metabolize xylose as a result of the absence of functional xylose permease, xylose isomerase, and xylulokinase activities, although it and both P. ruminicola and S. ruminantium possess the essential enzymes of the nonoxidative branch of the pentose phosphate cycle.

The agronomic performance of anther culture derived plants of barley produced via pollen embryogenesis

SummaryAnther culture was used to generate microspore‐derived doubled haploid (DH) plants from four spring barley crosses. The culture medium used contained maltose as the sole carbohydrate source and the mode of plantlet regeneration was mainly via pollen embryogenesis. Both haploid and spontaneously doubled regenerants were produced and the doubled haploids were compared to recom‐binant inbred lines generated by several rounds of selfing (single seed descent). Parental, DH and single seed descent (SSD) lines were grown in randomised, replicated field trials and the samples were scored for a range of agronomic traits. The mean performance and phenotypic distribution of the DH and SSD samples were similar and there was little evidence to support the conclusion that anther culture derived lines exhibit a reduction in vigour. Where significant differences were detected between groups these were mainly confined to crosses which were segregating for the denso dwarfing gene. The differential transmission of particular regions of the barley genome may therefore influence and confound the expression of agronomic traits in DH populations. This is the first report of the agronomic performance of anther culture lines produced via pollen embryogenesis and the results are discussed in relation to the exploitation of anther culture technology in barley breeding.

Short‐Term Polycose Substitution for Lactose Reduces Calcium Absorption in Healthy Term Babies

SummaryA vitamin D‐independent paracellular and not saturable mechanism important for intestinal calcium absorption turned out to be less effective in lactose‐free diets. Twelve normal term babies with identical repletion levels of 25‐hydroxyvitamin D (25D) were fed sequentially with starting formulas that differed only in their carbohydrate sources: lactose (control) and polycose. A 3‐day test was performed after a 1‐week adjustment to the new diet. Fecal excretion of calcium was significantly higher in the lactose‐free formula period compared to the control one: 56.6 (13.9) versus 39.6 (12.8) mg/kg/day (p &lt; 0.02); subsequently, the net retention was considerably higher and statistically significant (p &lt; 0.01) for the control period versus the lactose‐free formula period: 99.4 (15.3) versus 78.1 (14.3). Plasma 25D values were 21.8 (9.1) and 23.7 (7.1) ng/ml at the beginning of the lactose and polycose periods, respectively, and 1,25‐dihydroxy‐vitamin‐D values were 64 (62) and 75 (45) pg/ml, not significant. Results suggest that formulas containing polycose as the sole carbohydrate source may reduce the intestinal absorption of calcium in term newborns, but determining long‐term biological significance requires further observation.

Short-term polycose substitution for lactose reduces calcium absorption in healthy term babies.

A vitamin D-independent paracellular and not saturable mechanism important for intestinal calcium absorption turned out to be less effective in lactose-free diets. Twelve normal term babies with identical repletion levels of 25-hydroxyvitamin D (25D) were fed sequentially with starting formulas that differed only in their carbohydrate sources: lactose (control) and polycose. A 3-day test was performed after a 1-week adjustment to the new diet. Fecal excretion of calcium was significantly higher in the lactose-free formula period compared to the control one: 56.6 (13.9) versus 39.6 (12.8) mg/kg/day (p less than 0.02); subsequently, the net retention was considerably higher and statistically significant (p less than 0.01) for the control period versus the lactose-free formula period: 99.4 (15.3) versus 78.1 (14.3). Plasma 25D values were 21.8 (9.1) and 23.7 (7.1) ng/ml at the beginning of the lactose and polycose periods, respectively, and 1,25-dihydroxyvitamin-D values were 64 (62) and 75 (45) pg/ml, not significant. Results suggest that formulas containing polycose as the sole carbohydrate source may reduce the intestinal absorption of calcium in term newborns, but determining long-term biological significance requires further observation.