H2O2 Production in Species of the Lactobacillus acidophilus Group: a Central Role for a Novel NADH-Dependent Flavin Reductase

Hydrogen peroxide production is a well-known trait of many bacterial species associated with the human body. In the presence of oxygen, the probiotic lactic acid bacterium Lactobacillus johnsonii NCC 533 excretes up to 1 mM H₂O₂, inducing growth stagnation and cell death. Disruption of genes commonly assumed to be involved in H₂O₂ production (e.g., pyruvate oxidase, NADH oxidase, and lactate oxidase) did not affect this. Here we describe the purification of a novel NADH-dependent flavin reductase encoded by two highly similar genes (LJ_0548 and LJ_0549) that are conserved in lactobacilli belonging to the Lactobacillus acidophilus group. The genes are predicted to encode two 20-kDa proteins containing flavin mononucleotide (FMN) reductase conserved domains. Reductase activity requires FMN, flavin adenine dinucleotide (FAD), or riboflavin and is specific for NADH and not NADPH. The K_m for FMN is 30 ± 8 μM, in accordance with its proposed in vivo role in H₂O₂ production. Deletion of the encoding genes in L. johnsonii led to a 40-fold reduction of hydrogen peroxide formation. H₂O₂ production in this mutant could only be restored by in trans complementation of both genes. Our work identifies a novel, conserved NADH-dependent flavin reductase that is prominently involved in H₂O₂ production in L. johnsonii.     

Mortality limits used in wind energy impact assessment underestimate impacts of wind farms on bird populations

1. The consequences of bird mortality caused by collisions with wind turbines are increasingly receiving attention. So‐called acceptable mortality limits of populations, that is, those that assume that 1%–5% of additional mortality and the potential biological removal (PBR), provide seemingly clear‐cut methods for establishing the reduction in population viability.
2. We examine how the application of these commonly used mortality limits could affect populations of the Common Starling, Black‐tailed Godwit , Marsh Harrier, Eurasian Spoonbill, White Stork, Common Tern, and White‐tailed Eagle using stochastic density‐independent and density‐dependent Leslie matrix models.
3. Results show that population viability can be very sensitive to proportionally small increases in mortality. Rather than having a negligible effect, we found that a 1% additional mortality in postfledging cohorts of our studied populations resulted in a 2%–24% decrease in the population level after 10 years. Allowing a 5% mortality increase to existing mortality resulted in a 9%–77% reduction in the populations after 10 years.
4. When the PBR method is used in the density‐dependent simulations, the proportional change in the resulting growth rate and carrying capacity was species‐independent and largely determined by the recovery factor (F_r). When F_r = 1, a value typically used for robust populations, additional mortality resulted in a 50%–55% reduction in the equilibrium density and the resulting growth rate. When F_r = 0.1, used for threatened populations, the reduction in the equilibrium density and growth rate was about 5%.
5. Synthesis and applications. Our results show that by allowing a mortality increase from wind farm collisions according to both criteria, the population impacts of these collisions can still be severe. We propose a simple new method as an alternative that was able to estimate mortality impacts of age‐structured stochastic density‐dependent matrix models.

     

Ferritin accumulation and uroporphyrin crystal formation in hepatocytes of C57BL/10 mice: a time-course study

To establish the time-sequence relationship between ferritin accumulation and uroporphyrin crystal formation in livers of C57BL/10 mice, a biochemical, morphological and morphometrical study was performed. Uroporphyria was induced by the intraperitoneal administration of hexachlorobenzene plus iron dextran and of iron dextran alone. Uroporphyrin crystal formation started in hepatocytes of mice treated with hexachlorobenzene plus iron dextran at 2 weeks and in mice treated with iron dextran alone at 9 weeks. In the course of time, uroporphyrin crystals gradually increased in size. Uroporphyrin crystals were initially formed in hepatocytes in the periportal areas of the liver, in which also ferric iron staining was first detected. The amount and the distribution of the main storage form of iron in hepatocytes, ferritin, did not differ between the two treatment groups. Ferritin accumulation preceded the formation of uroporphyrin crystals in hepatocytes in both treatment groups. Moreover, uroporphyrin crystals were nearly always found close to ferritin iron. We conclude that uroporphyrin crystals are only formed in hepatocytes in which also iron (ferritin) accumulates. Hexachlorobenzene accelerates the effects of iron in porphyrin metabolism, but does not influence the accumulation of iron into the liver.     

An accurate method for the quantitation of Fmoc-derivatized solid phase supports

Summary By performing the Fmoc resin loading determination with DBU instead of piperidine, highly reproducible results were obtained that showed excellent correlation with data obtained by independent analytical methods.     

Diurnal buoyancy changes of Microcystis in an artificially mixed storage reservoir

In a storage reservoir, which is artificially mixed in order to reduce algal and especially cyanobacterial growth, the cyanobacterium Microcystis is still present. The aim of the research was to investigate why Microcystis was able to grow in the artificially mixed reservoir. From the results it could be concluded that the large shallow area in the reservoir allows this growth. The loss of buoyancy during the day was much higher in this shallow part than in the deep part. Assuming that the loss of buoyancy was the result of a higher carbohydrate content, a higher growth rate in the shallow part may be expected. A higher received light dose by the phytoplankton in the shallow mixed part of the reservoir than in the deep mixed part explains the difference in buoyancy loss. A significant correlation between the received light dose (calculated for homogeneously mixed phytoplankton) and the buoyancy loss was found. Apparently, the Microcystis colonies were entrained in the turbulent flow in both the shallow and the deep part of the reservoir. With a little higher stability on one sampling day, due to the late start of the artificial mixing, the loss of buoyancy at the deep site was higher than on the other days and almost comparable to the loss at the shallow site. Although the vertical biomass distribution and the temperature profiles showed homogeneous mixing, the colonies in the upper layers apparently received a higher light dose than those deeper in the water column. Determination of the buoyancy state of cyanobacteria appeared to be a valuable method to investigate the light history and hence their entrainment in the turbulent flow in the water column.     

Essential oil of two chemotypes of Mentha suaveolens during ontogenesis

The composition of the main constituents of the essential oil of two different chemotypes of Mentha suaveolens has been investigated during development. In the first chemotype (6) a definite increase of 1,2-epoxymen-thylacetate was observed, but piperitone oxide was always the main constituent. In the second chemotype (12) an increase of neo- and dihydrocarveol and their corresponding acetates was observed and dihydrocarvone was the main constituent. The results have been used to formulate a new biosynthetic scheme for the cyclic oxygenated monoterpenes found in essential oils of the genus Mentha.