Resistance of Pseudomonas to Quaternary Ammonium Compounds: II. Cross-Resistance Characteristics of a Mutant of Pseudomonas aeruginosa

Tube dilution experiments showed that benzalkonium chloride (BC)-resistant mutants of Pseudomonas aeruginosa grown in the presence of 1,000 mug of BC per ml were at least 20 times more sensitive to polymyxin B and colistin sulfate than the BC-sensitive (BCS) parent strain. BCS cells selected for resistance to 500 mug of polymyxin B per ml remained sensitive to BC. There was little difference in the amount of carbenicillin, gentamicin sulfate, or rifampin needed to prevent growth of either the BCS or BC-resistant (BCR) strains. Growth of BCR cells was inhibited by ethylenediaminetetraacetate at a concentration of 400 mug/ml or less, whereas the BCS strain grew at ethylenediaminetetraacetate levels of 10,000 mug/ml. Phenylmercuric acetate and thimerosal inhibited growth of BCR and BCS cells at concentrations of 10 mug/ml or less. BCR cells were cross-resistant to >1,000 mug/ml concentrations of five other quaternary ammonium compounds, including three with C(16) alkyls and two with alkyl groups of shorter length. The BCS strain was also resistant to >1,000 mug/ml concentrations of the three quaternary ammonium compounds with C(16) alkyl groups but, in addition to BC, was inhibited by 200 mug/ml levels or less of the two quaternary ammonium compounds containing alkyl groups of less than 16 carbon atoms.     

Earlier diagnosis and survival in lung cancer

In a controlled investigation the survival prospects of lung cancer in a population of men aged 40 and over who had been offered six-monthly chest radiographs over a period of three years were compared with lung cancer in a similar population without such x-ray facilities. The five-year survival rate of lung cancer in the study series was 15%, and in cases discovered by six-monthly examination 23%, compared with 6% in the control series. The average expectation of life after diagnosis was 2·5 years for the test cases and 1·2 for the control cases. Survival declined with age. Of resected lung cancer, 32% survived five years in the test series and 23% in the control series. The five-year survival rate for squamous carcinoma and adenocarcinoma in the test series was 28% and 25% respectively, compared with 15% and nil in the control series.On the basis of these results it is concluded that through earlier radiological detection a modest improvement in the prognosis of lung cancer can be achieved.     

Lipid composition and food quality of some freshwater phytoplankton for cladoceran zooplankters

The nutritional value of several planktonic algae was testedby means of feeding trials with three cladoceran zooplankters.The algae were monocultures and included two blue-greens, fourgreens and four flagellates with a size range of 5–48µm. The specific growth rates of the zooplankters werechosen as the measure of the nutritional value of the algae.The three cladocerans showed large differences in growth ratein the different algae, but the two cryptomonads were withoutdoubt best suited as food for all. The fatty acid compositionfor the cryptomonads were different from the other algae. Theycontained high percentages of the polyunsaturated fatty acids20:5æ3 (EPA) and 22:6æ3 (DHA), which also are commonin fish. It is suggested that the lipid composition is a probablefactor determining the nutritional quality of the algae.     

Genetic variation,breeding system evolution,and conservation of the narrow sand dune endemic Stellaria arenicola and the widespread S. longipes (Caryophyllaceae)

Genetic variation was examined by electrophoresis in 14 populations of Stellaria arenicola, an endemic of the Athabasca sand dunes in northern Saskatchewan, Canada, and seven populations of S. longipes, its progenitor. Three of the 5. longipes populations were sympatric with the endemic. Populations of the endemic were found to have fewer alleles per polymorphic locus (2.21 vs. 2.37), fewer polymorphic loci (29.9 vs. 33.8), and lower genetic diversity (0.087 vs. 0.107) than populations of the progenitor. Genetic identities for all pairs of populations were high (0.932 to 1.000). The endemic had one novel allele and shared ten alleles with progenitor populations from the sand dunes that were not found in other populations of S. longipes. Populations of both species were found to partition most of their genetic variation within populations. An investigation of the multilocus outcrossing rates revealed that S. arenicola had higher rates of selling and biparental inbreeding than S. longipes. This study suggests that partial genetic isolation through a shift in the breeding system, in addition to previously reported strong directional selection, has been important in the sympatric evolution of the endemic S. arenicola. The close genetic relationship between populations of S. arenicola and S. longipes found on the Athabasca sand dunes supports the suggestion that the endemic evolved while sympatric to the gene pool of the progenitor species that is found presently in the region.     

Crab: snail size-structured interactions and salt marsh predation gradients

We studied size-structured predator-prey interactions between blue crabs (Callinectes sapidus) and marsh periwinkles (Littoraria irrorata) with a combination of field studies, laboratory experiments and individual-based modeling. Size distributions of Littoraria differed among years at the same sites in a salt marsh and could largely be explained by dominance of strong cohorts in the population. At a given site, abundance increased with elevation above tidal datum. Size-selective predation by blue crabs does not appear to be an important regulator of snail size distributions but may have a major effect on local abundance. Laboratory studies indicated that predator-prey interactions between Callinectes and Littoraria are strongly size-dependent. Crabs were generally effective at feeding on periwinkles at size ratios greater than approximately 6 (crab width: snail length). At lower size ratios crabs were far less effective at manipulating the snails, which often survived but with damaged shells. An individual-based model which incorporated information about incidence of snail shell scarring (resulting from non-lethal interactions) and snail density, predicted reduced predation rates and smaller average crab size with distance from the low tide refugium for crabs.     

Characterization of genetic markers in the 5′ flanking region of the apo A1 gene

Genetic variation of apoA1/C3/A4 is associated with hyperlipidaemia and coronary heart disease. We report the polymerase chain reaction (PCR) conditions for determining three polymorphic sites in the 5 flanking region of apoA1 using DNA prepared from small aliquots of whole blood. These polymorphisms identify six haplotypes that will be of value in genetic studies.     

Pyric Herbivory and the Nexus Between Forage,Fire and Native and Introduced Large Grazing Herbivores in Australian Tropical Savannas

Earth’s tropical savannas typically support high biomass of diverse grazing herbivores that depend on a highly fluctuating resource: high-quality forage. An annual wet–dry cycle, fire and herbivory combine to influence forage quality and availability throughout the year. In the savannas of northern Australia, a depauperate suite of large native (marsupial) herbivores (wallaroos [Osphranter spp.] and the agile wallaby [Notamacropus agilis]) compete for resources with non-native large herbivores introduced in the late nineteenth century, particularly bovines (feral and managed cattle [Bos spp.] and feral water buffalo [Bubalus bubalis]) that now dominate the landscape. Anecdotal reports of recent population declines of large macropods and negative impacts of bovines highlight the need to better understand the complex relationship between forage, fire and abundance of native and introduced large herbivores. The pyric herbivory conceptual model, which posits complex feedbacks between fire and herbivory and was developed outside Australia, predicts that native and introduced large herbivores will both respond positively to post-fire forage production in Australian savannas where they co-occur. We used grazing exclosures, forage biomass and nutrient analyses and motion-sensor camera-trapping to evaluate the overall robustness of the pyric herbivory model in the Australian context, specifically whether forage quantity and quality are impacted by herbivory, season and fire activity, and which forage attributes most influence large grazing herbivore abundance. Forage quantity, as measured by live, dead and total herbaceous biomass and proportion of biomass alive, was higher inside herbivore exclosures, even at relatively low densities of herbivores. Forage quality, as measured by fibre content, was not affected by herbivory, however, crude protein content of live herbaceous biomass was greater outside herbivore exclosures. Recent fire was an important predictor of all measures of forage quantity and quality. Recent fire occurrence decreased overall quantity (biomass) but increased quality (decreased fibre content and increased crude protein content); late dry season fires resulted in forage with the highest crude protein content. The predictions of the pyric herbivory conceptual model are consistent with observations of the feeding behaviour of introduced bovines and some large macropods in northern Australian savannas, lending support to the global generality of pyric herbivory in fire-prone grassy biomes.

     

Environmental formation of methylmercury is controlled by synergy of inorganic mercury bioavailability and microbial mercury-methylation capacity

Methylmercury (MeHg) production is controlled by the bioavailability of inorganic divalent mercury (Hg(II)_i) and Hg-methylation capacity of the microbial community (conferred by the hgcAB gene cluster). However, the relative importance of these factors and their interaction in the environment remain poorly understood. Here, metagenomic sequencing and a full-factorial MeHg formation experiment were conducted across a wetland sulfate gradient with different microbial communities and pore water chemistries. From this experiment, the relative importance of each factor on MeHg formation was isolated. Hg(II)_i bioavailability correlated with the dissolved organic matter composition, while the microbial Hg-methylation capacity correlated with the abundance of hgcA genes. MeHg formation responded synergistically to both factors. Notably, hgcA sequences were from diverse taxonomic groups, none of which contained genes for dissimilatory sulfate reduction. This work expands our understanding of the geochemical and microbial constraints on MeHg formation in situ and provides an experimental framework for further mechanistic studies.     

The ecological drivers and consequences of wildlife trade

Wildlife trade is a key driver of extinction risk, affecting at least 24% of terrestrial vertebrates. The persistent removal of species can have profound impacts on species extinction risk and selection within populations. We draw together the first review of characteristics known to drive species use – identifying species with larger body sizes, greater abundance, increased rarity or certain morphological traits valued by consumers as being particularly prevalent in trade. We then review the ecological implications of this trade-driven selection, revealing direct effects of trade on natural selection and populations for traded species, which includes selection against desirable traits. Additionally, there exists a positive feedback loop between rarity and trade and depleted populations tend to have easy human access points, which can result in species being harvested to extinction and has the potential to alter source–sink dynamics. Wider cascading ecosystem repercussions from trade-induced declines include altered seed dispersal networks, trophic cascades, long-term compositional changes in plant communities, altered forest carbon stocks, and the introduction of harmful invasive species. Because it occurs across multiple scales with diverse drivers, wildlife trade requires multi-faceted conservation actions to maintain biodiversity and ecological function, including regulatory and enforcement approaches, bottom-up and community-based interventions, captive breeding or wildlife farming, and conservation translocations and trophic rewilding. We highlight three emergent research themes at the intersection of trade and community ecology: (1) functional impacts of trade; (2) altered provisioning of ecosystem services; and (3) prevalence of trade-dispersed diseases. Outside of the primary objective that exploitation is sustainable for traded species, we must urgently incorporate consideration of the broader consequences for other species and ecosystem processes when quantifying sustainability.