Dynamic modeling of nitrogen removal for a three-stage integrated fixed-film activated sludge process treating municipal wastewater

Bioprocess and Biosystems Engineering - The integrated fixed-film activated sludge (IFAS) process is being increasingly used to enhance nitrogen removal for former activated sludge systems. The aim...     

Mutations in the alpha1 subunit of an L-type voltage-activated Ca2+ channel cause myotonia in Caenorhabditis elegans.

The control of excitable cell action potentials is central to animal behavior. We show that the egl-19 gene plays a pivotal role in regulating muscle excitation and contraction in the nematode Caenorhabditis elegans and encodes the alphal subunit of a homologue of vertebrate L-type voltage-activated Ca2+ channels. Semi-dominant, gain-of-function mutations in egl-19 cause myotonia: mutant muscle action potentials are prolonged and the relaxation delayed. Partial loss-of-function mutations cause slow muscle depolarization and feeble contraction. The most severe loss-of-function mutants lack muscle contraction and die as embryos. We localized two myotonic mutations in the sixth membrane-spanning domain of the first repeat (IS6) region, which has been shown to be responsible for voltage-dependent inactivation. A third myotonic mutation implicates IIIS4, a region involved in sensing plasma-membrane voltage change, in the inactivation process.     

On the non-existence of an optimal migration rate

 We show that an optimal migration rate may not exist in a population distributed over an infinite number of individual living sites if empty sites occur. This is the case when the mean number of offspring per individual μ is finite. We make the assumption of uniform migration to other sites whose rate is determined by the parent’s genotype or the offspring’s genotype at a single locus in a diploid hermaphrodite population undergoing random mating. In both cases, for μ small enough, any population at fixation would go to extinction. Moreover, in the latter case, for intermediate values of μ, the only fixation state that could resist the invasion of any mutant would lead the population to extinction. These are the two conditions for the non-existence of an optimal migration rate. They become less stringent as the cost for migration expressed by a coefficient of selection 1−β becomes larger, that is, closer to 1. The results are obtained assuming that the allele at fixation is either nondominant or dominant. Although the optimal migration rate is the same in both cases when it exists, the optimality properties may differ. Received 14 December 1995; received in revised form 5 April 1996     

Newcastle disease virus in double-crested cormorants in Alabama, Florida, and Mississippi.

In order to understand the epidemiology of Newcastle disease (ND) outbreaks in double-crested cormorants (Phalacrocorax auritus), a study was conducted on wintering migratory cormorants (P. a. auritus) in Alabama and Mississippi (USA) and non-migratory cormorants (P. a. floridanus) that breed in Florida (USA). Antibodies against ND virus were detected by the hemagglutination-inhibition method in sera from 86 of 183 (47%) migratory cormorants over-wintering in eight roosting sites in Alabama and Mississippi between November, 1997 and April, 1999. Titers ranged from 5 to 40. Antibody prevalences in sera collected from females in early winter (November and December) (26%) and late winter (February and March) (56%) were significantly different (P = 0.0007). None of 45 serum samples from 1- to 7-wk-old nestlings from 11 colonies in Florida during the 1997-98 and 1998-99 breeding seasons was positive. However, antibodies were detected in yolk samples from 98 of 126 (78%) eggs collected in these same colonies. Titers ranged from 4 to 256. The prevalence of antibodies in eggs collected from fresh-water colonies (63% prevalence, n = 30) and salt-water colonies (82% prevalence, n = 96) was significantly different (P = 0.041). ND virus was not isolated from tissues of 18 cormorants and cloacal and tracheal swabs from 202 cormorants collected in Alabama and Mississippi; virus was also not isolated from cloacal and tracheal swabs from 51 nestlings from Florida.     

Temperature, but not productivity or geometry, predicts elevational diversity gradients in ants across spatial grains

Aim  This research aims to understand the factors that shape elevational diversity gradients and how those factors vary with spatial grain. Specifically, we test the predictions of the species–productivity hypothesis, species–temperature hypothesis, the metabolic theory of ecology and the mid-domain effects null model. We also examine how the effects of productivity and temperature on richness depend on spatial grain.
Location  Deciduous forests along an elevational gradient in Great Smoky Mountains National Park, USA.
Methods  We sampled 22 leaf litter ant assemblages at three spatial grains, from 1-m² quadrats to 50 × 50 m plots using Winkler samplers.
Results  Across spatial grains, warmer sites had more species than did cooler sites, and primary productivity did not predict ant species richness. We found some support for the predictions of the metabolic theory of ecology, but no support for the mid-domain effects null model. Thus, our data are best explained by some version of a species–temperature hypothesis.
Main conclusions  Our results suggest that temperature indirectly affects ant species diversity across spatial grains, perhaps by limiting access to resources. Warmer sites support more species because they support more individuals, thereby reducing the probability of local extinction. Many of our results from this elevational gradient agree with studies at more global scales, suggesting that some mechanisms shaping ant diversity gradients are common across scales.     

Demonstration of Cholinesterase in Teeth

Human teeth have been studied by treatment with copper thio-choline, the method developed by Koelle for demonstrating activity of both specific and nonspecific cholinesterases. Freshly extracted teeth were collected and immediately sectioned on a cutting machine designed for calcified tissues. One series of teeth was sectioned sufficiently thin for microscopic study. Another series of teeth was bisected to expose the pulp chambers to the reagents. These teeth were divided into 5 experimental groups. The first group was treated with 10^-6M di-isopropylfluorophosphate (DFP) for 30 min at 37°C and then incubated with acetylthiocholine (AThCh) for 16 to 20 hr at 37°C in order to reveal the sites of activity of the specific enzyme, AChEase. The second group was incubated in a substrate of butyrylthiocholine (BuThCh) for 12 to 16 hr at 37°C to indicate the sites of the nonspecific ChEase. The third group was incubated in AThCh for 16 to 20 hr at 37°C without previous treatment by an inhibitor in order to reveal the presence and location of both the specific and nonspecific ChEase. The fourth and fifth groups were utilized as controls. Group 4 tissues were incubated without a substrate while those of group 5 were treated with DFP and then incubated with BuThCh. The specimens then were treated with ammonium sulfide to outline the sites of ChEase activity. The thin sections were mounted directly but the series of halved teeth were decalcified, embedded in paraffin, sectioned and then mounted. By these methods the presence and location of both specific and nonspecific ChEase activity were observed in human teeth. Concentration of specific ChEase was observed along the coronal aspect of the pulp chamber and along the course of the pulpal nerves. The nonspecific ChEase was observed throughout the pulpal tissue and appeared to be concentrated along the nerves and blood vessels. Neither series of control tissues exhibited any staining in the pulp tissue.