Concepts of occlusion: Australian evidence

Longitudinal studies of aboriginal children over a 20-year period have drawn attention to the wide variation in morphological features of the dentition and the way in which occlusal relationships develop. This paper summarizes some important determinants of optimal occlusal development, namely, tooth size relationships within and between dentitions, the patterns of alveolar growth, and tooth migrations during the transition from primary to permanent teeth and the nature of growth changes in the dental arches. Dental occlusion constantly changes throughout life in response to changing functional requirements. Observations limited to cross-sectional material provide an incomplete, and sometimes misleading, concept of dental occlusion and masticatory function.     

Reclassification of incompatibility group L (IncL) plasmids.

Plasmids classified as IncL are shown to be incompatible with plasmids of IncM and we propose to reclassify them as IncM.     

Comparative study of methods for the enumeration of total and fecal coliforms in the eastern oyster, Crassostrea virginica.

Violet red bile agar and Coli-Count Sampler (Millipore Corp.) procedures were shown to be acceptable alternatives to the standard most-probable-number method for monitoring relative coliform levels in oysters.     

A hydrogen-deuterium exchange study of the amide protons of polymyxin B by nuclear-magnetic-resonance spectroscopy.

1. Proton magnetic resonance spectra at 270 MHz of polymyxin B, a cationic oligopeptide antibiotic, show the influence of the inorganic counteranion present in solution. 2. Hydrogen-deuterium exchange rates for the amide protons are of two types, depending on whether the anion is monovalent or polyvalent. Polyvalent anions catalyse the acid-catalysed reaction more than the monovalent anions. 3. The structure in solution was monitored using the proton signals of the amides, the phenylalanine aromatic protons, and the leucine methyl and gamma-CH protons in several polymyxin salts. The temperature coefficients of the chemical shifts of the N-H protons are used to identify two beta turns in the cyclic ring of polymyxin B. The variation in chemical shift of the N-H protons, the aromatic protons and the leucine protons are correlated with anionic size and electronegativity.     

Interaction of radical anion probes with glucoamylase I from Aspergillus niger.

The radical anions (SCN)2.- and Br2.- produced during a pulse radiolysis of the respective potassium salts have been used to study the tryptophan residues of the glucoenzyme, glucoamylase I (EC 3.2.1.3.). At neutral pH, Br2.- reacted with the tryptophan residues of glucoamylase I as expected from previous studies of proteins and free amino acids. However, (SCN)2.- at neutral and high pH was surprisingly unreactive towards the native enzyme. Reaction did occur, however, between (SCN)2.- and glucoamylase from which one-third of the covalently bound carbohydrate had been removed, producing a tryptophyl radical. Reaction also occured between (SCN)2.- and glucoamylase I inactivated by treatment with sodium dodecyl sulphate, but the tryptophan residues were not involved. It is concluded from the results that two 'types' of tryptophan residues are found in glucoamylase I; both are attacked by Br2.- but only one type is attacked by (SCN)2.-.     

Intron-derived small RNAs for silencing viral RNAs in mosquito cells

Aedes aegypti and Ae. albopictus are the main vectors of mosquito-borne viruses of medical and veterinary significance. Many of these viruses have RNA genomes. Exogenously provided, e.g. transgene encoded, small RNAs could be used to inhibit virus replication, breaking the transmission cycle. We tested, in Ae. aegypti and Ae. albopictus cell lines, reporter-based strategies for assessing the ability of two types of small RNAs to inhibit a chikungunya virus (CHIKV) derived target. Both types of small RNAs use a Drosophila melanogaster pre-miRNA-1 based hairpin for their expression, either with perfect base-pairing in the stem region (shRNA-like) or containing two mismatches (miRNA-like). The pre-miRNA-1 stem loop structure was encoded within an intron; this allows co-expression of one or more proteins, e.g. a fluorescent protein marker tracking the temporal and spatial expression of the small RNAs in vivo. Three reporter-based systems were used to assess the relative silencing efficiency of ten shRNA-like siRNAs and corresponding miRNA-like designs. Two systems used a luciferase reporter RNA with CHIKV RNA inserted either in the coding sequence or within the 3’ UTR. A third reporter used a CHIKV derived split replication system. All three reporters demonstrated that while silencing could be achieved with both miRNA-like and shRNA-like designs, the latter were substantially more effective. Dcr-2 was required for the shRNA-like siRNAs as demonstrated by loss of inhibition of the reporters in Dcr-2 deficient cell lines. These positive results in cell culture are encouraging for the potential use of this pre-miRNA-1-based system in transgenic mosquitoes.     

Insights into the feeding ecology of the Seychelles Black Parrot Coracopsis barklyi using two monitoring approaches

Feeding ecology is an important factor for the survival of a species and knowledge of its parameters is a prerequisite for successful conservation work. In this study we describe the feeding ecology of the endemic Seychelles Black Parrot Coracopsis barklyi on Praslin, Seychelles, the only island on which this parrot is resident. We compared two methods to evaluate feeding choices: incidental observations and feeding walks on 25 transects in all habitat types. Black parrots fed on 46 different species, bringing the total number of known food plants to 53 species. They predominantly consumed endemic and native species (58% of observed feeding bouts), mainly their fruit pulp (in 68% of feeding bouts), followed by buds (15%) and seeds (37%) with occasional observations of leaves, bark and scale insects. The incidental method rendered many more observed bouts than the transect approach and the ratios of consumed species differed between methods but the transect results are regarded as more representative. The incidental method is not suitable for quantitative conclusions but complements the transect method, providing information about rarely occurring feeding events.     

Soil Carbon Turnover Measurement by Physical Fractionation at a Forest-to-Pasture Chronosequence in the Brazilian Amazon

The effect of conversion from forest-to-pasture upon soil carbon stocks has been intensively discussed, but few studies focus on how this land-use change affects carbon (C) distribution across soil fractions in the Amazon basin. We investigated this in the 20 cm depth along a chronosequence of sites from native forest to three successively older pastures. We performed a physicochemical fractionation of bulk soil samples to better understand the mechanisms by which soil C is stabilized and evaluate the contribution of each C fraction to total soil C. Additionally, we used a two-pool model to estimate the mean residence time (MRT) for the slow and active pool C in each fraction. Soil C increased with conversion from forest-to-pasture in the particulate organic matter (>250 μm), microaggregate (53–250 μm), and d-clay (<2 μm) fractions. The microaggregate comprised the highest soil C content after the conversion from forest-to-pasture. The C content of the d-silt fraction decreased with time since conversion to pasture. Forest-derived C remained in all fractions with the highest concentration in the finest fractions, with the largest proportion of forest-derived soil C associated with clay minerals. Results from this work indicate that microaggregate formation is sensitive to changes in management and might serve as an indicator for management-induced soil carbon changes, and the soil C changes in the fractions are dependent on soil texture.