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.     

High chromosomal sensitivity of Chinese hamster xrs 5 cells to restriction endonuclease induced DNA double-strand breaks

The cytogenetic effects of restriction endonucleases (RE) and X-rays were examined in the radiosensitive mutant Chinese hamster cell line xrs 5 and its normal parental line CHO K1. Cells were permeabilized with Sendai virus and exposed to Pvu II and Eco RV which induce blunt-ended double-strand breaks (dsb) in the DNA of cells, or Bam H1 and Eco R1 which induce cohesive-ended dsb with a four-base overlap. Treated cells were then assayed for the presence of metaphase chromosomal aberrations by sampling at multiple fixation times and in experiments where cells were exposed to graded series of RE concentrations. Exposure to X-rays or RE causing blunt-ended dsb was found to be between two and three times more effective in xrs 5 than in CHO K1 cells. We interpret this higher chromosomal sensitivity of xrs 5 cells as reflecting the reported defect in dsb repair in xrs 5. Both xrs 5 and CHO K1 cells yielded less aberrations after exposure to Bam H1 or Eco R1 than after exposure to Pvu II or Eco RV, confirming our previous results and demonstrating that cohesive-ended dsb are less damaging than blunt-ended dsb. Multiple fixation time experiments showed that the higher sensitivity of xrs 5 was evident at several different sampling times after treatment. Similarly the low yield of aberrations after exposure of cells to Bam H1 was evident at all sampling times. Overdispersion of chromosomal aberrations was observed in samples exposed to RE. This is thought to be due to a non-uniform permeabilization of the cell population to RE. Our results indicate that RE-induced dsb are handled by cells in a similar way to those arising during X-ray exposure.     

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.