Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18.

Salmonella enterica serovar Typhi (S. typhi) is the aetiological agent of typhoid fever, a serious invasive bacterial disease of humans with an annual global burden of approximately 16 million cases, leading to 600,000 fatalities. Many S. enterica serovars actively invade the mucosal surface of the intestine but are normally contained in healthy individuals by the local immune defence mechanisms. However, S. typhi has evolved the ability to spread to the deeper tissues of humans, including liver, spleen and bone marrow. Here we have sequenced the 4,809,037-base pair (bp) genome of a S. typhi (CT18) that is resistant to multiple drugs, revealing the presence of hundreds of insertions and deletions compared with the Escherichia coli genome, ranging in size from single genes to large islands. Notably, the genome sequence identifies over two hundred pseudogenes, several corresponding to genes that are known to contribute to virulence in Salmonella typhimurium. This genetic degradation may contribute to the human-restricted host range for S. typhi. CT18 harbours a 218,150-bp multiple-drug-resistance incH1 plasmid (pHCM1), and a 106,516-bp cryptic plasmid (pHCM2), which shows recent common ancestry with a virulence plasmid of Yersinia pestis.     

The decline of intensive intergenerational care of older people in Great Britain, 1985-1995

There are increasing concerns about the future availability of informal care for older people, particularly care by their children. This article explores past trends in the provision of informal care by children/children-in-law to their older parents/parents-in-law between 1985 and 1995 in Great Britain, using successive General Household Survey data. The article suggests that, during this period, there was a decline in co-resident intergenerational care and that this was associated with a decline in highly intensive intergenerational care. The article explores possible factors underlying these trends, in particular, demographic changes and changes in patterns of formal care for older people.     

Capture of hydroxymethylene and its fast disappearance through tunnelling

Singlet carbenes exhibit a divalent carbon atom whose valence shell contains only six electrons, four involved in bonding to two other atoms and the remaining two forming a non-bonding electron pair. These features render singlet carbenes so reactive that they were long considered too short-lived for isolation and direct characterization. This view changed when it was found that attaching the divalent carbon atom to substituents that are bulky and/or able to donate electrons produces carbenes that can be isolated and stored. N-heterocyclic carbenes are such compounds now in wide use, for example as ligands in metathesis catalysis. In contrast, oxygen-donor-substituted carbenes are inherently less stable and have been less studied. The pre-eminent case is hydroxymethylene, H-C-OH; although it is the key intermediate in the high-energy chemistry of its tautomer formaldehyde, has been implicated since 1921 in the photocatalytic formation of carbohydrates, and is the parent of alkoxycarbenes that lie at the heart of transition-metal carbene chemistry, all attempts to observe this species or other alkoxycarbenes have failed. However, theoretical considerations indicate that hydroxymethylene should be isolatable. Here we report the synthesis of hydroxymethylene and its capture by matrix isolation. We unexpectedly find that H-C-OH rearranges to formaldehyde with a half-life of only 2 h at 11 K by pure hydrogen tunnelling through a large energy barrier in excess of 30 kcal mol(-1).     

Shigella sonnei genome sequencing and phylogenetic analysis indicate recent global dissemination from Europe

Shigella are human-adapted Escherichia coli that have gained the ability to invade the human gut mucosa and cause dysentery, spreading efficiently via low-dose fecal-oral transmission. Historically, S. sonnei has been predominantly responsible for dysentery in developed countries but is now emerging as a problem in the developing world, seeming to replace the more diverse Shigella flexneri in areas undergoing economic development and improvements in water quality. Classical approaches have shown that S. sonnei is genetically conserved and clonal. We report here whole-genome sequencing of 132 globally distributed isolates. Our phylogenetic analysis shows that the current S. sonnei population descends from a common ancestor that existed less than 500 years ago and that diversified into several distinct lineages with unique characteristics. Our analysis suggests that the majority of this diversification occurred in Europe and was followed by more recent establishment of local pathogen populations on other continents, predominantly due to the pandemic spread of a single, rapidly evolving, multidrug-resistant lineage.     

Influence of previous temperature on stomatal response to osmotica

Zusammenfassung Die Spaltöffnungsweiten in der Epidermis von Blattscheiben ausNicotiana tabacum werden durch osmotisch wirksame Substanzen unterschiedlich beeinflusst, wenn die Pflanzen vorgängig bei verschiedenen Temperaturen aufwachsen. Bei 28°C sind die Spaltöffnungen der Blattstücke in osmotisch wirksamen Lösungen weniger geöffnet als in reinem Wasser, während sich bei einer Temperatur von 18°C die Spaltöffnungsweiten entgegengesetzt verhalten.

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Supported through the Center for the Biology of Natural Systems by National Institutes of Health Grant No. 5 P10 ES00139 and by Health Science Advancement Award No. 5 S04 FR06115 to Washington University from the National Institutes of Health.

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The technical assistance ofKathleen Dutson is gratefully acknowledged.