Survival of Clostridium botulinum Spores

Radiation survival curves of spores of Clostridium botulinum strain 33A exhibited an exponential reduction which accounted for most of the population, followed by a “tail” comprising a very small residual number [7 to 0.7 spore(s) per ml] which resisted death in the range between 3.0 and 9.0 Mrad dose levels. The “tail” was not caused by protective spore substances released into the suspensions during irradiation, by the presence of accumulated radiation “inactivated” spores, or by heat shock of pre-irradiated spores. The theoretical number of spore targets which must be inactivated by irradiation was estimated both by a graphical and by a computation method to be about 80, and the D value was calculated to be 0.295 and 0.396 Mrad, respectively, in buffer and in pork pea broth.     

Effect of Temperature of Liquid Nitrogen on Radiation Resistance of Spores of Clostridium botulinum

An apparatus consisting of a Dewar flask and a relay system controlling the flow of liquid nitrogen permitted the irradiation of samples in tin cans or Pyrex tubes at temperatures ranging from 0 ± 1.5 C to -194 ± 2 C. An inoculated pack comprising 320 cans of ground beef containing 5 × 10⁴ spores of Clostridium botulinum 33A per can (10 cans per radiation dose) was irradiated with Co⁶⁰ at 0 and -196 C. Incubation was carried out at 30 C for 6 months. Approximately 0.9 Mrad more radiation was required to inactivate the spores at -196 C than at 0 C. Cans irradiated at -196 C showed partial spoilage at 3.6 Mrad and no spoilage at 3.9 Mrad; the corresponding spoilage-no spoilage doses at 0 C were 2.7 and 3.0, respectively. The majority of positive cans swelled in 2 to 14 days; occasional swelling occurred as late as 20 days. At progressively higher doses, swelling was delayed proportionally to the radiation dose received. The remaining nonswollen cans had no toxin after 6 months of storage, although occasional cans contained very low numbers of viable spores comprising on the average 0.1% of the original spore inoculum. The D₁₀ values in phosphate buffer were 0.290 Mrad for 0 C and 0.396 Mrad for -196 C; in ground beef, the corresponding D₁₀ values were 0.463 Mrad and 0.680 Mrad, respectively. These D₁₀ values indicate that the lethal effect of γ rays decreased at -196 C as compared with 0 C by 13.5% in phosphate buffer, and by 47% in ground beef.     

GENETIC RELATEDNESS OF TWO POPULATIONS OF THE SOUTHERN ELEPHANT SEAL, MIROUNGA LEONINA

Blood samples from southern elephant seals ( Mirounga leonina ) from Heard and Macquarie Islands were surveyed electrophoretically for protein variation. Thirty proteins encoded by a minimum of 35 loci were screened, four of which were found to be polymorphic. Statistically significant differences in allele frequencies were found between the two populations at three loci. Heterozygosity estimates for the Heard and Macquarie island populations were 0.034 ± 0.020 (mean ± standard error) and O.029 ± 0.017 respectively, with a Nei distance of 0.007. The findings suggest that the two populations may have diverged genetically and very limited gene flow exists between the islands, a finding consistent with limited information from mark-recapture studies.     

Human non-lineage antigen,CD46 (HuLy-m5): purification and partial sequencing demonstrates structural homology with complement-regulating glycoproteins

CD46, until recently known as HuLy-m5, is a non-lineage restricted surface antigen ubiquitously expressed by almost all human cells except erythrocytes. The CD46 antigen is identified by the E4.3 monoclonal antibody (mAb) and exists at the surface of human peripheral blood lymphocytes (PBLs) as two acidic, non-disulfide bonded chains, and , ofM _r 66 000 and 56 000. Receptor density analysis showed that CD46 was of moderately low abundance on PBLs with 7.5×10³ molecules present on each cell. The two chains of CD46 were purified (144 000-fold) by immunoaffinity-chromatography with E4.3 mAb from the plasma membranes of a human spleen infiltrated with chronic myelogenous leukemia cells. Amino acid sequence analysis of the NH₂-terminal of both and chains yielded the same sequence; XEEPPQ/TFEAMELIGKPKPYYEIGE. Peptide mapping studies confirmed that both CD46 chains were closely related, except for one peptide fragment. This amino acid sequence is identical to that of the NH₂-terminal of the recently cloned membrane co-factor protein (MCP), a membrane protein that binds the C3b and C4b fragments of complement and acts as a co-factor for I protein-mediated decay of the complement convertases. CD46 shares a cross-reactive epitope with some primate retroviruses, and this may indicate that some retroviruses mimic the mechanisms used by autologous human cells to evade complement-mediated immune clearance. Offprint requests to: I. F. C. McKenzie.     

Sequence and genomic structure of the human adult skeletal muscle sodium channel alpha subunit gene on 17q.

The amino acid sequence of the sodium channel alpha subunit from adult human skeletal muscle has been deduced by cross-species PCR-mediated cloning and sequencing of the cDNA. The protein consists of 1836 amino acid residues. The amino acid sequence shows 93% identity to the alpha subunit from rat adult skeletal muscle and 70% identity to the alpha subunit from other mammalian tissues. A 500 kb YAC clone containing the complete coding sequence and two overlapping lambda clones covering 68% of the cDNA were used to estimate the gene size at 35 kb. The YAC clone proved crucial for gene structure studies as the high conservation between ion channel genes made hybridization studies with total genomic DNA difficult. Our results provide valuable information for the study of periodic paralysis and paramyotonia congenita, two inherited neurological disorders which are caused by point mutations within this gene.     

Oxygen transport in the blood of arctic mammals: adaptation to local heterothermia

Summary The oxygen binding of whole blood from humans and two arctic mammals, reindeer and muskox, has been studied as a function of carbon dioxide and temperature. All bloods display a marked Bohr effect with Bohr coefficients in the range –0.44––0.73. The Bohr effect is more pronounced at 20°C. The temperature sensitivity of reindeer and muskox blood expressed by the apparent heat of oxygenation, H, is almost three times lower than that of human HbA under the same experimental conditions. This thermodynamic difference gives special benefits to arctic mammals with large heterothermy by safeguarding oxygen unloading at very low ambient temperatures.