Molecular analysis of the F plasmid traVR region: traV encodes a lipoprotein.

The nucleotide sequences of the conjugative F plasmid transfer region genes, traV and traR, have been determined. The deduced amino acid sequence of TraV indicated that it may be a lipoprotein; this was confirmed by examining the effect of globomycin on traV-encoded polypeptides synthesized in minicells. An open reading frame that may represent a previously undetected transfer gene, now designated trbG, was identified immediately upstream of traV. The deduced product of traR was found to share amino acid similarity with proteins from the bacteriophages 186 and P2 and with the dosage-dependent dnaK suppressor DksA.     

Carbon assimilation patterns and growth of the introduced CAM plant Opuntia inermis in Eastern Australia

Summary The daily course of CO₂ and H₂O exchange in cladodes of Opuntia inermis was studied at four sites in Eastern Australia. On most occasions cladode water contents were high and nocturnal stomatal opening resulted in substantial uptake of CO₂ and synthesis of about 130 equiv cm^-2 of malic acid during the night. Under water stress nocturnal stomatal opening was confined to the latter part of the night and acid synthesis was reduced to about 40 equiv cm^-2. Night temperature had little effect on acid synthesis, which responded primarily to rainfall and changed from the stressed condition within 2–3 days in irrigation experiments. On many occasions following summer rainfall stomata opened for 4 h in the late afternoon permitting net CO₂ fixation which may contribute about 25% of the total carbon assimilated. This CO₂ fixation was insufficient to have a marked impact on the ₁₃C value of the Opuntia cladodes. CO₂ fixation in the light occurred in conjunction with maximum dark CO₂ fixation under mesic conditions. Dark CO₂ fixation rates were 3 to 5 times greater than those recorded in desert cacti under favorable conditions. Relative growth rates calculated on the basic of CO₂ exchange correspond to measured relative growth rates of 0.05 g g^-1 dry wt day^-1 which prevailed for 60–90 days in summer. The capacity for very active CO₂ fixation in the dark and light following summer rainfall and the capacity to persist at low levels of metabolic activity through summer drought are discussed in relation to the success of this introduced species in this habitat.     

The effect of the sagittal ridge angle on cartilage stress in the equine metacarpo-phalangeal (fetlock) joint

Fatigue failure of bones of the metacarpo-phalangeal (fetlock, MCP) joint is common in thoroughbred racehorses. Stresses within the fetlock joint cartilages are affected by the morphology of the third metacarpal bone (MC3) and proximal phalangeal bone, and the steepness of the median sagittal ridge of MC3 is believed to be associated with fracture. This study investigated the influence of the steepness of the sagittal ridge on cartilage stress distribution using a finite element model of the joint. Changes to the steepness of the sagittal ridge were made by applying a parabolic function to the mesh, creating four different models with sagittal ridge angles ranging from 95° to 105°. In the fetlock joint of Thoroughbred racehorses, sagittal ridge angles of >100° were associated with higher Von Mises stresses in cartilage at the palmar aspect of the condylar groove than such stresses in joints with sagittal ridge angles of <100°. Stresses were high in the specific region where fractures are known to originate in MC3. This aspect of morphology of the fetlock joint thus appears to play an important role in the magnitude and distribution of cartilage stresses, which, when acting on the underlying hard tissues of the articular calcified cartilage and subchondral bone may play a role in the initiation of fatigue fracture in the third metacarpal bone.     

Replication of staphylococcal multiresistance plasmids

Based on structural and functional properties, three groups of large staphylococcal multiresistance plasmids have been recognized, viz., the pSK1 family, pSK41-like conjugative plasmids, and beta-lactamase-heavy-metal resistance plasmids. Here we describe an analysis of the replication functions of a representative of each of these plasmid groups. The replication initiation genes from the Staphylococcus aureus plasmids pSK1, pSK41, and pI9789::Tn552 were found to be related to each other and to the Staphylococcus xylosus plasmid pSX267 and are also related to rep genes of several plasmids from other gram-positive genera. Nucleotide sequence similarity between pSK1 and pI9789::Tn552 extended beyond their rep genes, encompassing upstream divergently transcribed genes, orf245 and orf256, respectively. Our analyses revealed that genes encoding proteins related to the deduced orf245 product are variously represented, in several types of organization, on plasmids possessing six seemingly evolutionarily distinct types of replication initiation genes and including both theta-mode and rolling-circle replicons. Construction of minireplicons and subsequent functional analysis demonstrated that orf245 is required for the segregational stability of the pSK1 replicon. In contrast, no gene equivalent to orf245 is evident on the conjugative plasmid pSK41, and a minireplicon encoding only the pSK41 rep gene was found to exhibit a segregational stability approaching that of the parent plasmid. Significantly, the results described establish that many of the large multiresistance plasmids that have been identified in clinical staphylococci, which were formerly presumed to be unrelated, actually utilize an evolutionarily related theta-mode replication system.     

Characterization of proteases in the skin mucus of Atlantic salmon (Salmo salar) infected with the salmon louse (Lepeophtheirus salmonis) and in whole-body louse homogenate

As part of an investigation of the biochemical interactions between the salmon louse Lepeophtheirus salmonis and Atlantic salmon Salmo salar, we characterized protease activity in the skin mucus of noninfected Atlantic salmon and Atlantic salmon infected with L. salmonis and in an L. salmonis whole-body homogenate. Zymography revealed that mucus from infected salmon contained a series of low-molecular-mass (17-22 kDa) serine proteases that were not present in the mucus of noninfected salmon. Based on molecular mass, inhibition studies, and affinity chromatography, the series of proteases was identified as being trypsin-like. Similar proteases were observed in the L. salmonis homogenate and in mucus from noninfected Atlantic salmon following a 1-hr incubation with live L. salmonis. An antibody raised against Atlantic salmon trypsin failed to recognize any proteases in the mucus of noninfected salmon or infected salmon or in the L. salmonis homogenate. Collectively, these findings suggest that the trypsin-like proteases present in the mucus of infected Atlantic salmon were produced by L. salmonis, possibly to aid in feeding and evasion of host immune responses.     

The structure of the nasal chemosensory system in squamate reptiles. 2. Lubricatory capacity of the vomeronasal organ

The vomeronasal organ is a poorly understood accessory olfactory organ, present in many tetrapods. In mammals, amphibians and lepidosaurian reptiles, it is an encapsulated structure with a central, fluid-filled lumen. The morphology of the lubricatory system of the vomeronasal organ (the source of this fluid) varies among classes, being either intrinsic (mammalian and caecilian amphibian vomeronasal glands) or extrinsic (anuran and urodele nasal glands). In the few squamate reptiles thus far examined, there are no submucosal vomeronasal glands. In this study, we examined the vomeronasal organs of several species of Australian squamates using histological, histochemical and ultrastructural techniques, with the goal of determining the morphology of the lubricatory system in the vomeronasal organ. Histochemically, the fluid within the vomeronasal organ of all squamates is mucoserous, though it is uncertain whether mucous and serous constituents constitute separate components. The vomeronasal organ produces few secretory granules intrinsically, implying an extrinsic source for the luminal fluid. Of three possible candidates, the Harderian gland is the most likely extrinsic source of this secretion.