The rumen fermentation rates in individual lactating cows were measured in four different experiments. The results disclosed that the amounts and proportions of volatile acids formed could vary widely. In one case, a marked difference in the proportions of the acids produced arose within the experiment and correlated with a difference in the proportion of methane formed.
The average rate of production per day was 10.5 moles butyric acid, 12.8 moles propionic acid, and 40 moles acetic acid. Manometric estimations of rate gave lower results than those obtained by the zero-time method, due to delay after sampling and to failure of the acids to liberate stoichiometric quantities of carbon dioxide.
For those experiments in which zero-time rates were estimated, the average specific absorption rates, i.e., the amount absorbed per hour per micromole of acid in the rumen, were 0.37 for butyric acid, 0.38 for propionic acid, and 0.26 for acetic acid.
The carbon dioxide, acids, and microbial cells produced in the rumen fermentation are estimated to account for about 90% of the carbon found in the milk and respiratory CO2 of the cows. The carbon dioxide from the fermentation was about 27% of the carbon dioxide exhaled.
Compared to the catastrophic impacts of various environmental disturbances and the subsequent recovery of scleractinian coral communities from these events, little is known about the early successional dynamics of coral communities following major volcanic eruptions. The 1988 volcanic eruption of Gunung Api, Banda Islands, Indonesia, provided a unique opportunity to study the rate at which a reef-building coral community develops on an andesitic lava flow. Coral colonization was studied at three locations varying in substrate characteristics. Five years after the eruption, the sheltered lava flow supported a diverse coral community (124 species) with high coral cover
. Tabulate acroporids were a dominant component of the lava flow coral community, with some colonies measuring over 90 cm in diameter. Higher average coral diversity, coral abundance and cover were recorded on the andesitic lava flow than on an adjacent carbonate reef not covered by the lava, and on a substrate of unstable pyroclastic deposits located on the southwestern coast of the volcano. In some areas of high coral diversity and environmental stability, andesitic lava flows may create local hot-spots of coral diversity by providing a structurally complex, predator-free and stable substrate for the recruitment of coral species from the adjacent and regional species pools. 相似文献
The ATP-binding-cassette transmembrane transporters (ABC transporters)
known from vertebrates belong to four major subfamilies: (1) the P-
glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance
regulators (CFTR); (3) the Tap proteins encoded with the major
histocompatibility complex of mammals; and (4) the peroxisomal membrane
proteins. Both Pgp and CFTR have a structure suggesting a past internal
gene duplication; a phylogenetic analysis indicated that these duplications
occurred independently, while an independent tandem gene duplication
occurred in the case of the Tap family. Both the Pgp and Tap proteins show
evidence of relationship to bacterial ABC transporters lacking internal
duplication, and both are significantly more closely related to the HlyB
and MsbA families of transporters from purple bacteria than they are to ABC
transporters from nonpurple bacteria. The simplest hypothesis to explain
this observation is that eukaryotic Pgp and Tap genes are descended from a
mitochondrial gene or genes that were subsequently translocated to the
nuclear genome. The Pgp genes of eukaryotes are characterized by a
remarkable degree of convergent evolution between the ATP-binding cassettes
of their N- terminal and C-terminal halves, whereas no such convergence is
seen between the two halves of CFTR genes or between the duplicated Tap
genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain
not found in other ABC transporters apart from CFTR, showed high levels of
both synonymous and nonsynonymous difference in comparisons among different
mammalian species, suggesting that this region is a mutational hot spot.
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Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis. 相似文献
Abstract The 16S rRNA gene (rDNA) sequence analysis of four halophilic anaerobes: Halobacteroides halobius, H. lacunaris, Haloanaerobacter (Hb.) chitinovorans and H. acetoethylicus confirmed that they were all members of the family Haloanaerobiaceae. H. lacunaris and H. halobius were found to be more closely related to each other and were distantly related to Sporohalobacter lortetti and the members of the genera Haloanaerobium and Halothermothrix . These data are in agreement with their assignment to the genus Halobacteroides . Further analysis indicated that Hb. chitinovorans was closely affiliated to members of the genus Halobacteroides , and therefore we propose to transfer it to the genus Halobacteroides as H. chitinovorans comb. nov. This transfer would invalidate the genus Haloanaerobacter , as Hb. chitinovorans is the only member of this genus. The 16S rDNA sequence analysis of H. acetoethylicum indicated that it was very closely related to members of the genus Haloanaerobium , viz. Haloanaerobium (Ha.) praevalens, Ha. salsugo , and Ha. alcaliphilum , and hence we propose to transfer it to the genus Haloanaerobium as Ha. acetoethylicus comb. nov. 相似文献
A methanogenic acetate enrichment was initiated by inoculation of an acetate-mineral salts medium with domestic anaerobic digestor sludge and maintained by weekly transfer for 2 years. The enrichment culture contained a Methanosarcina and several obligately anaerobic nonmethanogenic bacteria. These latter organisms formed varying degrees of association with the Methanosarcina, ranging from the nutritionally fastidious gram-negative rod called the satellite bacterium to the nutritionally nonfastidious Eubacterium limosum. The satellite bacterium had growth requirements for amino acids, a peptide, a purine base, vitamin B12, and other B vitamins. Glucose, mannitol, starch, pyruvate, cysteine, lysine, leucine, isoleucine, arginine, and asparagine stimulated growth and hydrogen production. Acetate was neither incorporated nor metabolized by the satellite organism. Since acetate was the sole organic carbon source in the enrichment culture, organism(s) which metabolize acetate (such as the Methanosarcina) must produce substrates and growth factors for associated organisms which do not metabolize acetate. 相似文献
Ulcerative colitis is distinguished by abundant prostaglandin E2 (PGE2) in the stools and by severe diarrhea. To determine whether luminal PGE2 alters normal colonic absorption, Na+ and Cl−transport across isolated rat proximal colon were studied before and after 16, 16 dimethyl PGE2 (dmPGE2) addition to flux chambers. Luminal administration of dmPGE2 significantly reduced the net mucosal to serosal fluxes of Na+ and Cl−. These antiabsorptive tive effects of dmPGE2 on Na+ and Cl− active transport were reflected by a reduced metabolic rate of colonic tissue slices incubated with dmPGE2. Addition of dmPGE2 significantly reduced oxidation of glucose by the colon. Structurally, dmPGE2 reduced the length of colonic mucosal microvilli, thereby decreasing absorptive surface area. These results suggest that PGE2 released into the colonic lumen of patients with ulcerative colitis exerts antiabsorptive effects on the colon and in this way contributes to the associated diarrhea. 相似文献