Nutritionally limited pectinolytic bacteria from the human intestine.

A selective procedure was used to isolate pectinolytic intestinal bacteria from human subjects. The three isolates with the greatest pectinolytic activity utilized pectin and a few related compounds as fermentable substrates for growth but did not utilize any other compound tested. Thus, their substrate utilization pattern was markedly different from that of previously described intestinal pectinolytic isolates. The three isolates are representatives of a nutritionally defined group of bacteria for which the term pectinophilic is proposed.     

Activation of dolichyl-phospho-mannose synthase by phospholipids

Dolichyl-phospho-mannose synthase, or GDPmannose:dolichyl-phosphate mannosyltransferase (EC 2.4.1.83), was solubilized from rat liver microsomes with 1.0% Nonidet P-40 and the enzyme was further purified by column chromatography on DEAE-cellulose in the presence of 0.1% Nonidet P-40. The purified enzyme preparation (880-fold over microsomes) was unstable in the presence of detergent and had no activity in the presence of Nonidet P-40, Triton X-100, octyl beta-glucoside, or deoxycholate. Detergent-free enzyme was active in the presence of phosphatidylethanolamine (PtdEtn) and in the presence of phospholipid mixtures of PtdEtn and phosphatidylcholine (PtdCho) when the molar proportion of PtdCho was 70% or less. The enzyme was inactive in the presence of PtdCho alone. Unsaturated species of PtdEtn have a tendency to destabilize membrane bilayers [Cullis, P. R. & de Kruijff, B. (1978) Biochim. Biophys. Acta 507, 207-218] and we have shown that dolichol promotes the destabilizing effect of PtdEtn on membranes composed of PtdCho and PtdEtn [Jensen, J. W. & Schutzbach, J. S. (1984) Biochemistry 23, 115-1119]. These results suggest that dolichyl-P-mannose synthase is optimally active in a phospholipid matrix that contains some component phospholipids that prefer non-bilayer structural organization in isolation. Heat-inactivation and sedimentation experiments demonstrated that the synthase associated with PtdEtn in the presence of dolichyl-P. The PtdEtn-reconstituted enzyme catalyzed the reversible transfer of mannose from GDP-mannose to dolichyl-P. The Km for GDP-mannose was found to be 0.69 microM and the apparent Km for dolichyl-P was 0.3 microM. GMP, GDP, and GTP inhibited mannosyl transfer 50% at concentrations of 16 microM, 1.3 microM and 3 microM respectively.     

Neuropeptides in the gastrointestinal canal of Necturus maculosus

Summary The presence and distribution of regulatory peptides in nerves and endocrine cells of the stomach, intestine and rectum of a urodele amphibian, the mudpuppy, Necturus maculosus, was studied immunohistochemically in sections or whole-mount preparations of the gut wall. The effect of the occurring peptides on gut motility was studied in isolated strip preparations of circular and longitudinal smooth muscle from different parts of the gut.Bombesin-, neurotensin-, substance P- and VIP-like immunoreactivity was present in abundant nerve fibres in the myenteric plexus of both stomach, intestine and rectum. Single fibres or bundles were present in the circular muscle layer and in a well-developed deep muscular plexus in the intestine and rectum. Immunoreactive nerve cells were found in the myenteric plexus of the stomach, intestine (neurotensin only) and rectum. Gastrin/CCK-like immunoreactivity was observed only in a few fibres in stomach and rectum.Endocrine cells containing bombesin-, met-enkephalin-, gastrin/CCK-, neurotensin-, somatostatin- or substance P- like immunoreactivity were present in the mucosa.The effect of bombesin was an inhibition of the rhythmic activity in circular muscle preparations and in longitudinal muscle from the rectum, while longitudinal muscle from the stomach usually responded with a weak increase in tonus. Neurotensin, like bombesin, was inhibitory on the spontaneous rhythmic activity of circular muscle throughout the gut, while the effect on longitudinal muscle was an increase in tonus. Met-enkephalin and substance P increased the tonus of all types of preparations, and often, in addition, initiated a rhythmic activity superimposed on this maintained tonus. VIP had a general inhibitory effect on the preparations, decreasing tonus and/or abolishing rhythmic activity.It is concluded that bombesin-, neurotensin-, substance P- and VIP-like peptides are present in nerves throughout the urodele gut and may have physiological functions in regulating the motility of the gut. The gastrin/CCK-like peptide present in nerves of the stomach and rectum may affect the function of these parts of the gut. The regulatory peptides present in endocrine cells may, perhaps with the exception of the somatostatin-like peptide, affect the motility humorally.     

The Cladocera and Copepoda of the Alta water-course, Northern Norway

Cladocera and Copepoda fauna, from ten lakes in the Alta water-course,northern Norway, have been collected and investigated. A totalof 42 species (34 Cladocera and 8 Copepoda) were recorded. Thenumber of Cladoceran species is high when compared with thatregistered for other areas of similar latitude, and Cladoceranspecies abundance is also greater than that reported for otherregions of northern and central Scandinavia. In addition, themean number of planktonic species present at any given timein the lakes (4.9 Cladocera and 3.4 Copepoda) was comparativelyhigh. Eight species have never been recorded as existing farthernorth than the Alta water-course, Three other species have beenrecorded at higher latitudes in North America, but not in Eurasia.Several species, of which there are only a few published records,arc rare in northern Scandinavia, and nine species were notconsidered by Illies (1978), as existing in the region of thepresent study.     

The distribution and interconversion of ammonium and nitrate in the Skallingen salt marsh (Denmark) and their exchange with the adjacent coastal water

The potential nitrogen sources for the primary production in the intertidal area are nitrogen compounds obtained from mineralization in the sediment and the water column, nitrogen fixation, outflow from rivers and groundwater seeping from the mainland. The available inorganic nitrogen in the adjacent coastal waters decreases from 50–80 μmol NO₃ ^-/l and 6–15 μmol NH₄ ⁺/l in early spring to ca one tenth during the growing season. In the sediment of the tidal flats available ammonia and nitrate vary between 50 and 100 μmol/1 pw. In the salt marsh available ammonia increases from 200–300 nmol NH₄ ⁺/g fwt to approximately double the amount, and the available nitrate varies from 100–300 nmol NO₃ ^-/g fwt (250–750 μmol NO₃ ^-/l pw) to ca one third during the growing season. The exchange of NH₄ ⁺, NO₂ ^- and NO₃ ^- across the sediment water interface has been estimated during tidal cycles under light and dark conditions on the tidal flats. The flux of nitrogen was dependent on the flora and fauna as well as the time of the year. The tidal activity, frequency and length of inundation are considered the driving force in a two-way process between salt marshes and adjacent coastal waters. The role of marsh sediment, tidal water and sediments of the tidal flats as sites of accumulation, consumption and remineralization of organic matter is emphasized. The possible exchange of ammonia and nitrate between the salt marsh and the different compartments of the tidal water is discussed.     

On the ecophysiology of Halimione portulacoides

Growth rate and salt accumulation were investigated in experiments on Halimione portulacoides with seven sodium chloride treatments, in water culture. The growth of Halimione was found to be stimulated by moderate, 85–170 mM NaCl, levels of salinity, but increasingly depressed by salinities from 410–690 mM NaCl, which is comparable to salinities in salt marshes during the growing season. Using the same technique, growth rate, chloride and nitrogen uptake experiments at four different sodium chloride and nitrate treatment levels were conducted, in order to study the effect of nitrogen and salt. At 8 mM NaCl in the growth medium growth was depressed at 16.2 mM nitrate treatment levels. At 137 mM, 410 mM and 684 mM of NaCl growth was stimulated by increasing levels of nitrogen. The results of these experiments are discussed in relation to the nitrogen and salt conditions prevailing in Halimione portulacoides salt-marsh communities.     

Biochemical pathways in prokaryotes can be traced backward through evolutionary time

For the first time, a credible prokaryotic phylogenetic tree is being assembled by Woese and others using quantitative sequence analysis of oligonucleotides in the highly conservative rRNA. This provides an evolutionary scale against which the evolutionary steps that led to the arrangement and regulation of contemporary biochemical pathways can be measured. This paper presents an emerging evolutionary picture of aromatic amino acid biosynthesis within a large superfamily assemblage of prokaryotes that is sufficiently developed to illustrate a new perspective that will be applicable to many other biochemical pathways.      

Insulin-specific tolerance induction. I. Abrogation of helper T cell activity is controlled by H-2-linked Ir genes

Murine antibody responses to heterologous insulins are under H-2-linked immune response (Ir) gene control. We have found that the immune response to insulin in adjuvant can be inhibited by prior i.v. injection of soluble insulin. The effect of i.v. injection of insulin is antigen-specific and dose-dependent and requires the same doses of insulin that are immunogenic if administered with adjuvant. In addition, the inhibitory effect of soluble insulin is dependent upon the route of injection; if soluble insulin is injected i.p., the subsequent response to insulin in adjuvant is augmented rather than inhibited. Unresponsiveness requires at least 4 days after i.v. injection to develop and once induced, it is maintained for 4 wk or more. Unresponsiveness is caused by T cell, but not B cell, tolerance, and we have been unable to demonstrate any role for suppressor T cells in this unresponsiveness. More importantly, analysis of the ability of numerous insulin variants to induce unresponsiveness in several H-2k and H-2b strains of mice has demonstrated that only the variants that were immunogenic in a given strain when administered with adjuvant were able to cause tolerance. This report is, to our knowledge, the first describing that induction of helper T cell tolerance, like the induction of immunity, is controlled by H-2-linked Ir genes.     

Clues from Xanthomonas campestris about the evolution of aromatic biosynthesis and its regulation

The recent placement of major Gram-negative prokaryotes (Superfamily B) on a phylogenetic tree (including, e.g., lineages leading to Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter calcoaceticus) has allowed initial insights into the evolution of the biochemical pathway for aromatic amino acid biosynthesis and its regulation to be obtained. Within this prokaryote grouping, Xanthomonas campestris ATCC 12612 (a representative of the Group V pseudomonads) has played a key role in facilitating deductions about the major evolutionary events that shaped the character of aromatic biosynthesis within this grouping. X. campestris is like P. aeruginosa (and unlike E. coli) in its possession of dual flow routes to both L-phenylalanine and L-tyrosine from prephenate. Like all other members of Superfamily B, X. campestris possesses a bifunctional P-protein bearing the activities of both chorismate mutase and prephenate dehydratase. We have found an unregulated arogenate dehydratase similar to that of P. aeruginosa in X. campestris. We separated the two tyrosine-branch dehydrogenase activities (prephenate dehydrogenase and arogenate dehydrogenase); this marks the first time this has been accomplished in an organism in which these two activities coexist. Superfamily B organisms possess 3-deoxy-D-arabino-heptulosonate 7-P (DAHP) synthase as three isozymes (e.g., in E. coli), as two isozymes (e.g., in P. aeruginosa), or as one enzyme (in X. campestris). The two-isozyme system has been deduced to correspond to the ancestral state of Superfamily B. Thus, E. coli has gained an isozyme, whereas X. campestris has lost one. We conclude that the single, chorismate-sensitive DAHP synthase enzyme of X. campestris is evolutionarily related to the tryptophan-sensitive DAHP synthase present throughout the rest of Superfamily B. In X. campestris, arogenate dehydrogenase, prephenate dehydrogenase, the P-protein, chorismate mutase-F, anthranilate synthase, and DAHP synthase are all allosteric proteins; we compared their regulatory properties with those of enzymes of other Superfamily B members with respect to the evolution of regulatory properties. The network of sequentially operating circuits of allosteric control that exists for feedback regulation of overall carbon flow through the aromatic pathway in X. campestris is thus far unique in nature.