Nutrient Uptake and Mineralization during Leaf Decay in Streams – a Model Simulation

We developed a stoichiometrically explicit computer model to examine how heterotrophic uptake of nutrients and microbial mineralization occurring during the decay of leaves in streams may be important in modifying nutrient concentrations. The simulations showed that microbial uptake can substantially decrease stream nutrient concentrations during the initial phases of decomposition, while mineralization may produce increases in concentrations during later stages of decomposition. The simulations also showed that initial nutrient content of the leaves can affect the stream nutrient concentration dynamics and determine whether nitrogen or phosphorus is the limiting nutrient. Finally, the simulations suggest a net retention (uptake > mineralization) of nutrients in headwater streams, which is balanced by export of particulate organic nutrients to downstream reaches. Published studies support the conclusion that uptake can substantially change stream nutrient concentrations. On the other hand, there is little published evidence that mineralization also affects nutrient concentrations. Also, there is little information on direct microbial utilization of nutrients contained in the decaying leaves themselves. Our results suggest several directions for research that will improve our understanding of the complex relationship between leaf decay and nutrient dynamics in streams. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interactions between rumen anaerobic fungi and ciliate protozoa in the degradation of rice straw cell walls

Suspensions of mixed rumen protozoa were added to incubations of the anaerobic fungus Neocallimastix patriciarum with rice straw cell walls. The protozoa did not influence the dry matter lost from the straw, or the solubilization of monosaccharides, but they had a marked effect on the fermentation products formed. Studies with ¹⁴C-labelled protozoa suggested that the presence of protozoa reduced the fungal carboxymethylcellulase activity to around half of that found in pure cultures of the fungus.     

Exposure to diethylstilbestrol during pregnancy permanently alters the ovary and oviduct

To determine the effects of transplacental exposure to diethylstilbestrol (DES) on the ovary and oviduct of the CD-1 mouse, timed pregnant mice were injected subcutaneously with DES (100 micrograms/kg) on Days 9 through 16 of gestation and female offspring sacrificed from 4 weeks to 10 months of age. Following DES exposure, ovarian alterations such as inflammation, a prominent interstitial compartment composed of medullary tubule-like structures, and intra- and para-ovarian cysts from mesonephric remnants were observed. In addition, there were oviductal abnormalities including malformation. As reported previously, the oviduct was closely adherent and coiled around the ovary in a similar position to that seen in the fetal mouse. This malformation was termed developmental arrest of the oviduct (DAO) and was a consistent finding in female offspring exposed prenatally to DES (100 micrograms/kg). Increased prevalence of salpingitis and microscopic alterations in the oviduct were also observed. Oviductal epithelium was mostly secretory type with basal vacuoles. In some cases, oviductal epithelium was hyperplastic and formed mucosal folds resembling glands which extended through the muscularis (diverticulosis). The extent of the adenomatous mucosal folds and the degree of extension through the muscularis increased with the age of the animal (100% at 10 months). Some characteristics of this abnormality resembled salpingitis isthmica nodosa, a lesion described in women which is associated with ectopic pregnancies and subfertility. Gross and microscopic changes in the oviduct were more consistent than were the changes among other portions of the reproductive tract of DES-treated mice previously reported. Since subfertility has been described in this mouse model as well as in prenatally DES-exposed women, the data presented in this report may help in evaluation of the reported reduced fertility in exposed patients as well as other infertility patients.     

Assessment of ciliates in the sheep rumen by DGGE

AIMS: This work was carried out to develop a rapid molecular profiling technique to screen ciliate populations in the rumen of sheep. METHODS AND RESULTS: DGGE was used to study the ciliate diversity in the rumen of sheep. There was considerable variation between sheep which were co-housed, and fed the same diet. However, no difference in the major banding patterns was detected, when samples were collected from a single sheep sampled at different points. Following dietary changes, use of a pair-wise comparison of lanes, demonstrated that although there was still diversity between the ciliate population of sheep, the effects as a result of dietary changes were greater. CONCLUSIONS: The technique generated molecular profiles which are sufficiently different to allow comparison between samples, and to permit molecular ecological studies on the rumen ciliate population. SIGNIFICANCE AND IMPACT OF THE STUDY: The outcome of this study means that ciliate diversity in the rumen may now be studied by those unfamiliar with morphological identification of these organisms.     

Identification and characterization of avihepadnaviruses isolated from exotic anseriformes maintained in captivity

Five new hepadnaviruses were cloned from exotic ducks and geese, including the Chiloe wigeon, mandarin duck, puna teal, Orinoco sheldgoose, and ashy-headed sheldgoose. Sequence comparisons revealed that all but the mandarin duck viruses were closely related to existing isolates of duck hepatitis B virus (DHBV), while mandarin duck virus clones were closely related to Ross goose hepatitis B virus. Nonetheless, the S protein, core protein, and functional domains of the Pol protein were highly conserved in all of the new isolates. The Chiloe wigeon and puna teal hepatitis B viruses, the two new isolates most closely related to DHBV, also lacked an AUG start codon at the beginning of their X open reading frame (ORF). But as previously reported for the heron, Ross goose, and stork hepatitis B viruses, an AUG codon was found near the beginning of the X ORF of the mandarin duck, Orinoco, and ashy-headed sheldgoose viruses. In all of the new isolates, the X ORF ended with a stop codon at the same position. All of the cloned viruses replicated when transfected into the LMH line of chicken hepatoma cells. Significant differences between the new isolates and between these and previously reported isolates were detected in the pre-S domain of the viral envelope protein, which is believed to determine viral host range. Despite this, all of the new isolates were infectious for primary cultures of Pekin duck hepatocytes, and infectivity in young Pekin ducks was demonstrated for all but the ashy-headed sheldgoose isolate.     

A central role for Bid in granzyme B-induced apoptosis

Granzyme B, a protease released from cytotoxic lymphocytes, has been proposed to induce target cell death by cleaving and activating the pro-apoptotic Bcl-2 family member Bid. It has also been proposed that granzyme B can induce target cell death by activating caspases directly, by cleaving caspase substrates, and/or by cleaving several non-caspase substrates. The relative importance of Bid in granzyme B-induced cell death has therefore remained unclear. Here we report that cells isolated from various tissues of Bid-deficient mice were resistant to granzyme B-induced cell death. Consistent with the proposed role of Bid in regulating mitochondrial outer membrane permeabilization, cytochrome c remained in the mitochondria of Bid-deficient cells treated with granzyme B. Unlike wild type cells, Bid-deficient cells survived and were then able to proliferate normally, demonstrating the critical role for Bid in mediating granzyme B-induced apoptosis.     

An NAD(+)-dependent glutamate dehydrogenase cloned from the ruminal ciliate protozoan, Entodinium caudatum

An NAD(+)-dependent glutamate dehydrogenase (GDH; EC 1.4.1.24) was cloned from the ruminal ciliate protozoan, Entodinium caudatum. The gene had high sequence similarity to GDH genes from the Bacteroides (class)--a class of bacteria which is highly represented in the rumen. When expressed in Escherichia coli the enzyme had a high affinity for ammonia and alpha-ketoglutarate (apparent K(m) of 2.33 and 0.71 mM, respectively) and a low affinity for glutamate (apparent K(m) of 98 mM). GDH activity and GDH mRNA concentration were increased by incubating washed E. caudatum cells with ammonia and antibiotics. These results suggest that the GDH is an anabolic enzyme catalysing the assimilation of ammonia by E. caudatum in the rumen and that the gene was probably acquired by lateral gene transfer from a ruminal bacterium.