Nitrosospira spp. can produce nitrous oxide via a nitrifier denitrification pathway

Nitrous oxide (N2O) emission from soils is a major contributor to the atmospheric loading of this potent greenhouse gas. It is thought that autotrophic ammonia oxidizing bacteria (AOB) are a significant source of soil-derived N2O and a denitrification pathway (i.e. reduction of NO2- to NO and N2O), so-called nitrifier denitrification, has been demonstrated as a N2O production mechanism in Nitrosomonas europaea. It is thought that Nitrosospira spp. are the dominant AOB in soil, but little information is available on their ability to produce N2O or on the existence of a nitrifier denitrification pathway in this lineage. This study aims to characterize N2O production and nitrifier denitrification in seven strains of AOB representative of clusters 0, 2 and 3 in the cultured Nitrosospira lineage. Nitrosomonas europaea ATCC 19718 and ATCC 25978 were analysed for comparison. The aerobically incubated test strains produced significant (P < 0.001) amounts of N2O and total N2O production rates ranged from 2.0 amol cell(-1) h(-1), in Nitrosospira tenuis strain NV12, to 58.0 amol cell(-1) h(-1), in N. europaea ATCC 19718. Nitrosomonas europaea ATCC 19718 was atypical in that it produced four times more N2O than the next highest producing strain. All AOB tested were able to carry out nitrifier denitrification under aerobic conditions, as determined by production of N-15-N2O from applied N-15-NO2-. Up to 13.5% of the N2O produced was derived from the exogenously applied N-15-NO2-. The results suggest that nitrifier denitrification could be a universal trait in the betaproteobacterial AOB and its potential ecological significance is discussed.

Effects of essential oils on ruminal microorganisms and their protein metabolism

A commercial blend of essential oil (EO) compounds was added to a grass, maize silage, and concentrate diet fed to dairy cattle in order to determine their influence on protein metabolism by ruminal microorganisms. EO inhibited (P < 0.05) the rate of deamination of amino acids. Pure-culture studies indicated that the species most sensitive to EO were ammonia-hyperproducing bacteria and anaerobic fungi.

Corrosion by sulfate reducing bacteria that utilize nitrate

16S rRNA gene sequencing was used to identify a sulfate-reducing bacterium (SRB) from a Danish North Sea oilfield water injection system. This species was cultivated, purified and subsequently identified as being >97% similar to Desulfovibrio gracilis. Like some other Desulfovibrio species this SRB, strain OP102, could reduce nitrate as an electron acceptor and produce ammonia in the absence of sulfate. In addition, in the presence of sulfate, when nitrate was dosed at 100 mg/l it was again reduced by the bacterium, with some ammonium production. Therefore, this mechanism could be important in oilfield systems where nitrate is applied to prevent sulfide generation by SRB which leads to reservoir souring. In static tests the influence of this Desulfovibrio on corrosion was assessed using carbon steel coupons, in the presence of sulfate and in the presence of sulfate with 100 mg/l nitrate. Corrosion rates were less than 1.5 mpy when coupons were incubated in the same water, with sulfate and with nitrate. Furthermore, the occurrence of pitting corrosion was fairly low under all circumstances.

Soft topographic map for clustering and classification of bacteria

In this work a new method for clustering and building a topographic representation of a bacteria taxonomy is presented. The method is based on the analysis of stable parts of the genome, the so-called “housekeeping genes”. The proposed method generates topographic maps of the bacteria taxonomy, where relations among different type strains can be visually inspected and verified. Two well known DNA alignement algorithms are applied to the genomic sequences. Topographic maps are optimized to represent the similarity among the sequences according to their evolutionary distances. The experimental analysis is carried out on 147 type strains of the Gammaprotebacteria class by means of the 16S rRNA housekeeping gene. Complete sequences of the gene have been retrieved from the NCBI public database. In the experimental tests the maps show clusters of homologous type strains and present some singular cases potentially due to incorrect classification or erroneous annotations in the database.

Optimal protection of stabilised dry live bacteria from bile toxicity in oral dosage forms by bile acid adsorbent resins

We previously found that dried live bacteria of a vaccine strain can be temporarily sensitive to bile acids and suggested that Bile Adsorbing Resins (BAR) can be used in oral vaccine tablets to protect dried bacteria from intestinal bile. Here, we report a quantitative analysis of the ability of BAR to exclude the dye bromophenol blue from penetrating into matrix tablets and also sections of hard capsule shells. Based on this quantitative analysis, we made a fully optimised formulation, comprising 25% w/w of cholestyramine in Vcaps™ HPMC capsules. This gave effectively 100% protection of viability from 4% bile, with 4200-fold more live bacteria recovered from this formulation compared to unprotected dry bacteria. From the image analysis, we found that the filler material or compaction force used had no measurable effect on dye exclusion but did affect the rate of tablet hydration. Increasing the mass fraction of BAR gave more exclusion of dye up to 25% w/w, after which a plateau was reached and no further dye exclusion was seen. More effective dye exclusion was seen with smaller particle sizes (i.e. cholestyramine) and when the BAR was thoroughly dried and disaggregated. Similar results were found when imaging dye penetration into capsule sections or tablets. The predictions of the dye penetration study were tested using capsules filled with dried attenuated Salmonella vaccine plus different BAR types, and the expected protection from bile was found, validating the imaging study. Surprisingly, depending on the capsule shell material, some protection was given by the capsule alone without adding BAR, with Vcaps™ HPMC capsules providing up to 174-fold protection against 1% bile; faster releasing Vcaps Plus™ HPMC capsules and Coni Snap™ gelatin capsules gave less protection.

Protection of live bacteria from bile acid toxicity using bile acid adsorbing resins

We previously demonstrated that a dry, room temperature stable formulation of a live bacterial vaccine was highly susceptible to bile, and suggested that this will lead to significant loss of viability of any live bacterial formulation released into the intestine using an enteric coating or capsule. We found that bile and acid tolerance is very rapidly recovered after rehydration with buffer or water, raising the possibility that rehydration in the absence of bile prior to release into the intestine might solve the problem of bile toxicity to dried cells. We describe here a novel formulation that combines extensively studied bile acid adsorbent resins with the dried bacteria, to temporarily adsorb bile acids and allow rehydration and recovery of bile resistance of bacteria in the intestine before release. Tablets containing the bile acid adsorbent cholestyramine release 250-fold more live bacteria when dissolved in a bile solution, compared to control tablets without cholestyramine or with a control resin that does not bind bile acids. We propose that a simple enteric coated oral dosage form containing bile acid adsorbent resins will allow improved live bacterial delivery to the intestine via the oral route, a major step towards room temperature stable, easily administered and distributed vaccine pills and other bacterial therapeutics

Microbial control of diamondback moth, Plutella xylostella L. (Lepidoptera:Yponomeutidae) using bacteria (Xenorhabdus nematophila) and its metabolites from the entomopathogenic nematode Steinernema carpocapsae

Cells and cell-free solutions of the culture filtrate of the bacterial symbiont, Xenorhabdus nematophila taken from the entomopathogenic nematode Steinernema carpocapsae in aqueous broth suspensions were lethal to larvae of the diamondback moth Plutella xylostella. Their application on leaves of Chinese cabbage indicated that the cells can penetrate into the insects in the absence of the nematode vector. Cell-free solutions containing metabolites were also proved as effective as bacterial cells suspension. The application of aqueous suspensions of cells of X. nematophila or solutions containing its toxic metabolites to the leaves represents a possible new strategy for controlling insect pests on foliage.

Biological control of black vine weevil (Otiorhynchus sulcatus, Coleoptera: Curculionidae) by entomopathogenic bacteria and their cell-free toxic metabolites

Biocontrol agents such as Xeiwrhabduf, nemalophilci and X. nematophila ssp. bovienii and their cell-free protein toxin complexes were lethal to larvae of O. sulcatus when applied to potting compost in the absence of plants. Similarly, strawberry plants infected with 0. sulcaitfi larvae were protected from damage by applications of both cell suspensions of the bacteria and solutions of their cell-free toxic metabolites, indicating that it is the protein toxins, which are responsible for the lethal effects observed. These toxic metabolites were found more effective against 0. sulccitus larvae when treated in soil microflora. Insect mortality is increased by increasing temperature and bacterial concentration. The toxins remained pathogenic for several months when stored in potting soil either at 15 or 20°C, however, bacterial cells were not as persistent as the toxins. It is therefore suggested that these bacteria and their toxic metabolites can he applied in soil for insect pest control.

Splanchnic metabolism of nitrogenous compounds and urinary nitrogen excretion in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera

Effects of increased ammonia and/or arginine absorption across the portal-drained viscera (PDV) on net splanchnic (PDV and liver) metabolism of nitrogenous compounds and urinary N excretion were investigated in six cathetenzed Hereford x Angus steers (501 +/- 1 kg BW) fed a 75% alfalfa:25% (as-fed basis) corn-soybean meal diet (0.523 MJ of ME/[kg BW0.15.d]) every 2 h without (27.0 g of N/kg of dietary DM) and with 20 g of urea/kg of dietary DM (35.7 g of N/kg of dietary DM) in a split-plot design. Net splanchnic flux measurements were obtained immediately before beginning and ending a 72-h mesenteric vein infusion of L-arginine (15 mmol/h). For 3 d before and during arginine infusion, daily urine voided was measured and analyzed for N composition. Feeding urea increased PDV absorption (P < 0.01) and hepatic removal (P < 0.01) of ammonia N, accounting for 80% of increased hepatic urea N output (P < 0.01). Numerical increases in net hepatic removal of AA N could account for the remaining portion of increased hepatic urea N output. Arginine infusion increased hepatic arginine removal (P < 0.01) and hepatic urea N output (P < 0.03) and switched hepatic ornithine flux from net uptake to net output (P < 0.01), but numerical changes in net hepatic removal of ammonia and AA N could not account fully for the increase in hepatic urea N output. Increases in urine N excretion equaled quantities of N fed as urea or infused as arginine. Estimated salivary urea N excretion was not changed by either treatment. Urea cycle regulation occurs via a complex interaction of mechanisms and requires N sources other than ammonia, but the effect of increased ammonia absorption on hepatic catabolism of individual AA in the present study was not significant.

Splanchnic metabolism of nutrients and hormones in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera

Effects of increased ammonia and/or arginine absorption on net splanchnic (portal-drained viscera [PDV] plus liver) metabolism of nonnitrogenous nutrients and hormones in cattle were examined. Six Hereford x Angus steers (501 +/- 1 kg BW) prepared with vascular catheters for measurements of net flux across the splanchnic bed were fed a 75% alfalfa:25% (as-fed basis) corn and soybean meal diet (0.523 MJ of ME/[kg BW(0.75.)d]) every 2 h without (27.0 g of N/kg of DM) and. with 20 g of urea/kg of DM (35.7 g of N/kg of DM) in a split-plot design. Net flux measurements were made immediately before and after a 72-h mesenteric vein infusion Of L-arginine (15 mmol/h). There were no treatment effects on PDV or hepatic 02 consumption. Dietary urea had no effect on splanchnic metabolism of glucose or L-lactate, but arginine infusion decreased net hepatic removal Of L-lactate when urea was fed (P < 0.01). Net PDV appearance of n-butyrate was increased by arginine infusion (P < 0.07), and both dietary urea (P < 0.09) and arginine infusion (P < 0.05) increased net hepatic removal of n-butyrate. Dietary urea also increased total splanchnic acetate output (P < 0.06), tended to increase arterial glucagon concentration (P < 0.11), and decreased arterial ST concentration (P < 0.03). Arginine infusion increased arterial concentration (P < 0.07) and net PDV release (P < 0.10) and tended to increase hepatic removal (P < 0.11) of insulin, as well as arterial concentration (P < 0.01) and total splanchnic output (P < 0.01) of glucagon. Despite changes in splanchnic N metabolism, increased ammonia and arginine absorption had little measurable effect on splanchnic metabolism of glucose and other nonnitrogenous components of splanchnic energy metabolism.

Steinernema feltiae: ammonia triggers the emergence of their infective juveniles

Entomopathogenic nematodes complete their life cycles inside dead insects. The emergence of new infective juveniles from the cadaver has been attributed (but never demonstrated) to food depletion or to the accumulation of metabolites from the breakdown of the host's tissues. Here we give evidence that emergence is triggered by ammonia, a product of nematode defecation. We found that the emergence of Steinernema feltiae infective juveniles from Galleria mellonella cadavers was stimulated by a particular level of ammonia. Emergence was delayed when ammonia in the cadaver was decreased and was prompted when increased. These findings will further improve the understanding of the nematode life cycle. Here we speculate that production of infective juveniles can be mediated by ammonia and work in a manner analogous to that of the clatter recovery inhibiting factor (DRIF) in Caenorhabditis elegans. (C) 2008 Elsevier Inc. All rights reserved.