Pulling or drilling, does size or species matter? An experimental study of prey handling in Octopus dierythraeus ()

The influence of both predator and prey size on the shift from a pulling to a drilling predatory response was examined in the intertidal octopus Octopus dierythraeus, using an experimental program. Additionally, selective drilling, where particular regions of the prey are targeted, was examined for a variety of bivalve and gastropod prey. O. dierythraeus always initially attempted to pull bivalves apart. Shells that were eventually drilled were always subjected to significantly more pulling attempts than those that could be pulled apart, indicating that octopus are willing to expend more energy to access the flesh quickly. There was no defined threshold where bivalve size caused an octopus to switch from a pulling to a drilling response. Instead, there was a broad size range where the octopus could adopt either handling method and it varied for each individual. Octopus may only able to pull open bivalves before the molecular ratchet or ‘catch’ mechanism that many bivalves possess is engaged. This might explain the lack of a relationship between either octopus or bivalve size and the success of pulling, as it is likely that when the bivalves were presented to individual octopus they were either setting the ‘catch’ mechanism, or had already engaged it. O. dierythraeus demonstrated selective drilling on a variety of molluscan prey, with penetration sites differing between prey species. O. dierythraeus targeted the valve periphery, which was the thinnest part of the shell, therefore minimizing handling time. O. dierythraeus always drilled gastropods, but did not target the thinnest regions of the shells, with drill site varying according to the morphology of the prey. Elongate species with pronounced aperture lips were drilled in the apical region, close to the columella on the side of the opercula whereas nonelongate species were drilled immediately above the aperture. The location of drilling sites may represent a trade-off between targeting the most effective places to inject paralyzing secretions and the mechanically simplest places to drill.     

Alternations in lipid membrane fluidity and the physical state of cell-surface sialic acid in zinc-deficient rat erythrocyte ghosts

Erythrocyte ghosts, prepared from the blood of rats fed zinc-deficient diets, were evaluated for membrane fluidity and surface sialic acid properties using spin-labeled probes and electron spin resonance (ESR) spectroscopy. These physical parameters of the erythrocyte ghosts from the zinc-deficient group were compared to those for erythrocyte ghosts obtained from ad libitum and pair fed controls consuming zinc-adequate diets. As the animals became progressively zinc deficient, the erythrocyte ghost membranes became more fluid than those from the control groups. In addition, the apparent rotational correlation time of Tempamine spin probes on surface sialic acid residues was smaller for the zinc deficient group, indicative of an increased rotational mobility of the spin label. These results suggest that zinc deficiency can have pronounced effects on the physical state of membrane bilayer lipids and cell surface carbohydrates and supports the view that many of the pathological signs of zinc deficiency are due to a general membrane defect.     

Extracellular production of a heat-stable somatic antigen by Bacillus thuringiensis

Extracellular production of a heat-stable somatic antigen (HSSA) by Bacillus thuringiensis subsp. dendrolimus strain T84A1-A [flagellar (H) serotype 4a: 4b] was serologically detected. In Ouchterlony tests, the HSSA antiserum gave single precipitin lines against both untreated and heat-treated culture supernatants. These two precipitin lines fused completely. When colonies of strain T84A1-A were grown on nutrient agar plates containing the homologous HSSA antiserum, precipitin halos were formed around the colonies. Of 27 type strains of B. thuringiensis subspecies tested, only the type strains of B. thuringiensis subsp. sotto (H serotype 4a: 4b) and B. thuringiensis subsp. israelensis (H serotype 14) formed [precipitin halos on nutrient agar plates containing antiserum against the HSSA of strain T84A1-A.     

Purification and some properties of the methyl-CoM reductase of Methanothrix soehngenii

Abstract The methyl-CoM reductase from Methanothrix soehngenii was purified 18-fold to apparent homogeneity with 50% recovery in three steps. The native molecular mass of the enzyme estimated by gel-fitration was 280 kDa. SDS-polyacrylamide gel electrophoresis revealed three protein bands corresponding to M _r 63 900, 41 700 and 30 400 Da. The methyl-coenzyme M reductase constitutes up to 10% of the soluble cell protein. The enzyme has K _m apparent values of 23 μM and 2 mM for N -7-mercaptoheptanoylthreonine phosphate (HS- HTP = component B ) and methyl-coenzyme M (CH₃CoM) respectively. At the optimum pH of 7.0 60 nmol of methane were formed per min per mg protein.