Synergism within polyhexamethylene biguanide biocide formulations

Polyhexamethylene biguanides (PHMB) are mixtures of polymeric biguanides with an average polymer length (n) of 5, but containing high (n greater than 15, mol. wt 3300) and low molecular weight material (n = 2, mol. wt 400). Studies involving discrete molecular weight fractions of PHMB have shown that antimicrobial activity of PHMB increases with increasing polymer length. Cell suspensions which had not been subjected to centrifugation and/or washing during their preparation were employed. Whilst activity was still observed to increase with n, the trend was much reduced as n exceeded six. Centrifugation and washing of cells markedly increased the activity of high but not low molecular weight materials and corresponded to losses upon centrifugation of envelope lipopolysaccharide (LPS). Such envelope LPS represented high affinity binding sites on the surfaces of the cells. Combinations of various molecular weight fractions of PHMB were evaluated against filter-washed cells and revealed a profound synergy between extremes of polymer length.     

Transformation of Rhodopseudomonas sphaeroides with deoxyribonucleic acid isolated from bacteriophage R phi 6P.

The transformation of the photosynthetic bacterium Rhodopseudomonas sphaeroides with the circular genome of the penicillinase-encoding, temperate bacteriophage R phi 6P was demonstrated. The transformation was dependent on the infection of the recipient by another, apparently closely related, temperature bacteriophage, R phi 9. Optimum transformation occurred in the recipient cells already lysogenic for R phi 9 when superinfected with that bacteriophage at multiplicities of infection between 1 and 10 R phi 9 particles per recipient cell.     

Chick embryo fibroblasts produce two forms of hyaluronidase

Cultured chick embryo fibroblasts derived from skin and skeletal muscle exhibit hyaluronidase activity both associated with the cell layer and secreted into the medium. Although both forms of the enzyme have a number of similar characteristics (R.W. Orkin and B.P. Toole, 1980, J. Biol. CHem. 255), they differ in thermal stability at neutral pH and in behavior on ion-exchange chromatography. Both forms of the enzyme are equally stable at acidic pH for long intervals, but the cell-associated hyaluronidase is significantly less stable than the secreted froms at neutral pH and at temperatures more than or equal to 30 degrees C. Neither the presence of proteases nor inhibitors of hyaluronidase appear to be involved in the cell-asspcoated enzyme. Chromatography of the two forms of hyaluronidase on carboxymethyl cellulose reveals that most (60-90 percent) of the secreted form of the enzyme elutes at a lower ionic strength than the cell- associated enzyme. Treatment of the secreted form of hyaluronidase with neuraminidase shifts its elution profile on carboxymethyl cellulose toward that of the cell-associated form, and also decreases its thermal stability at neutral pH. In contrast, treatment of the secreted form of hyaluronidase with alkaline phosphatase has no detectable effect. These data suggest that the secreted hyaluronidase differs from the cellular form in possessing additional sialic acid residues which endow the former with increased stability in the extracellular milieu.     

History of Ichnology: Early Ichnology Poems and Their Poets

In the early nineteenth century, the discovery of trace fossils fired the imagination of the discoverers and inspired them to compose unique poems. John Joly of Ireland wrote a poem about the invertebrate trace fossil Oldhamia that had been discovered in rocks around Bray Head. In the United States, the Reverend Edward Hitchcock discovered what he felt were giant bird tracks that later turned out to be reptile tracks. The traces inspired Hitchcock, who published a poem “The Sandstone Bird” in The Knickerbocker magazine under the pseudonym Poetaster. The poem is about a sorceress bringing the great sandstone bird back to life and probably represents the first ichnological poem.     

History of Ichnology: The Correspondence Between the Reverend Henry Duncan and the Reverend William Buckland and the Discovery of the First Vertebrate Footprints

The Reverend Henry Duncan (1774–1846), clergyman, philosopher, writer, politician, archeologist, poet, educator, social reformer, and the founder of savings banks, was indeed a Man for All Seasons. In 1824, while Minister of the Church of Scotland at Ruthwell, Dumfriesshire, he was presented with a slab of red sandstone from the Corncockle Muir quarry in Annandale, exhibiting a set of footprints on it. Although Duncan felt from the start that he was dealing with the tracks of an animal, he wrote to the Reverend William Buckland, Reader in Mineralogy and Geology at the University of Oxford, to solicit his opinion on the origin of these curious markings. Buckland was at first skeptical, but after receiving casts of the markings from Duncan, he became convinced that they did in fact represent footprints. Duncan and Buckland maintained a correspondence about the footprints, and on January 7, 1828, Duncan described the Corncockle Muir footprints to the Royal Society of Edinburgh and quoted Buckland's findings. Duncan's paper was not published by the Society until 1831, but it aroused considerable interest—“Footsteps before the Flood”!—and was reported in several newspapers. This was the first scientific report of a fossil track; although a schoolboy, Pliny Moody, had found fossil footprints in Connecticut in 1802, they were not scientifically described until 1836. The Scottish tracks are now considered to be not reptilian but of synapsid origin and the rocks containing them are now known to be of Permian age.     

Characterization of stable, constitutively expressed, chromosomal green and red fluorescent transcriptional fusions in the select agent bacterium, Francisella tularensis Schu S4 and the surrogate type B live vaccine strain (LVS)

Here, we constructed stable, constitutively expressed, chromosomal green (GFP) and red fluorescent (RFP) reporters in the genome of the surrogate strain, Francisella tularensis spp. holarctica LVS (herein LVS), and the select agent, F. tularensis Schu S4. A bioinformatic approach was used to identify constitutively expressed genes. Two promoter regions upstream of the FTT1794 and rpsF(FTT1062) genes were selected and fused with GFP and RFP reporter genes in pMP815, respectively. While the LVS strains with chromosomally integrated reporter fusions exhibited fluorescence, we were unable to deliver the same fusions into Schu S4. Neither a temperature-sensitive Francisella replicon nor a pBBR replicon in the modified pMP815 derivatives facilitated integration. However, a mini-Tn7 integration system was successful at integrating the reporter fusions into the Schu S4 genome. Finally, fluorescent F. tularensis LVS and a mutant lacking MglA were assessed for growth in monocyte-derived macrophages (MDMs). As expected, when compared to wild-type bacteria, replication of an mglA mutant was significantly diminished, and the overall level of fluorescence dramatically decreased with infection time. The utility of the fluorescent Schu S4 strain was also examined within infected MDMs treated with clarithromycin and enrofloxacin. Taken together, this study describes the development of an important reagent for F. tularensis research, especially since the likelihood of engineered antibiotic resistant strains will emerge with time. Such strains will be extremely useful in high-throughput screens for novel compounds that could interfere with critical virulence processes in this important bioweapons agent and during infection of alveolar macrophages.     

Introgression and the fate of domesticated genes in a wild mammal population

When domesticated species are not reproductively isolated from their wild relatives, the opportunity arises for artificially selected variants to be re‐introduced into the wild. However, the evolutionary consequences of introgression of domesticated genes back into the wild are poorly understood. By combining high‐throughput genotyping with 25 years of long‐term ecological field data, we describe the occurrence and consequences of admixture between a primitive sheep breed, the free‐living Soay sheep of St Kilda, and more modern breeds. Utilizing data from a 50 K ovine SNP chip, together with forward simulations of demographic scenarios, we show that admixture occurred between Soay sheep and a more modern breed, consistent with historical accounts, approximately 150 years ago. Haplotype‐sharing analyses with other breeds revealed that polymorphisms in coat colour and pattern in Soay sheep arose as a result of introgression of genetic variants favoured by artificial selection. Because the haplotypes carrying the causative mutations are known to be under natural selection in free‐living Soay sheep, the admixture event created an opportunity to observe the outcome of a ‘natural laboratory’ experiment where ancestral and domesticated genes competed with each other. The haplotype carrying the domesticated light coat colour allele was favoured by natural selection, while the haplotype associated with the domesticated self coat pattern allele was associated with decreased survival. Therefore, we demonstrate that introgression of domesticated alleles into wild populations can provide a novel source of variation capable of generating rapid evolutionary changes.     

Testosterone and cortisol concentrations vary with reproductive status in wild female red deer

Although hormones are key regulators of many fitness and life history traits, the causes of individual level variation in hormones, particularly in wild systems, remain understudied. Whilst we know that androgen and glucocorticoid levels vary within and among individuals in mammalian populations, how this relates to key reproductive processes such as gestation and lactation, and their effects on a female''s measurable hormone levels are poorly understood in wild systems. Using fecal samples collected from females in a wild red deer population between 2001 and 2013, we explore how fecal androgen (FAM) and cortisol (FCM) metabolite concentrations change with age and season, and how individual differences relate to variation in reproductive state. Both FAM and FCM levels increase toward parturition, although this only affects FCM levels in older females. FCM levels are also higher when females suckle a male rather than a female calf, possibly due to the higher energetic costs of raising a son. This illustrates the importance of accounting for a female''s life history and current reproductive status, as well as temporal variation, when examining individual differences in hormone levels. We discuss these findings in relation to other studies of mammalian systems and in particular to the relatively scarce information on variation in natural levels of hormones in wild populations.