Human-associated extended-spectrum ß-lactamase in the Antarctic.

Escherichia coli bacteria with extended-spectrum ß-lactamase (ESBL) type CTX-M resistance were isolated from water samples collected close to research stations in Antarctica. The isolates had bla(CTX-M-1) and bla(CTX-M-15) genotypes and sequence types (ST) indicative of a human-associated origin. This is the first record of ESBL-producing enterobacteria from Antarctica.

Baseline concentrations of trace metals in macroalgae from the Strait of Magellan, Chile.

Samples of four different species of seaweed were collected monthly between October 2000 and March 2001 from the coast of the Strait of Magellan, Chile to establish baseline levels of trace metals (silver, total mercury, nickel, lead, antimony, vanadium and zinc) and to compare the accumulation capacity among species. The algae included in the study were Adenocystis utricularis (n=15); Enteromorpha sp. (n=11), Mazzaella laminarioides (n=12) and Porphyra columbina (n=6). The concentration range of each metal in microg g(-1) dry weight varied as follows: Ag=ND-0.3, Hg=ND-0.02, Ni=ND-12.6, Pb = ND-11.2, Sb=ND-1.97, V=ND-11.34 and Zn=14.10-79. Results showed that levels of Ag, Hg, Ni, Pb, Sb, V and Zn for all species were similar to those found in other studies for non-contaminated areas with very little influence from anthropogenic activity. Also among the four species studied macroalgae Enteromorpha sp. had the highest capacity for metal accumulation and could therefore be considered as a biomonitor for future studies in the area.

Arabidopsis thaliana avoids freezing by supercooling.

Arabidopsis thaliana (L.) Heynh. has been described as a freezing-tolerant species based on freezing-resistance assays. Nonetheless, this type of experiment does not discriminate between freezing-tolerance and freezing-avoidance mechanisms. The purpose of this paper was to determine which of these two freezing-resistance mechanisms is responsible for freezing resistance in A. thaliana. This was achieved by comparing the thermal properties (ice-nucleation temperature and the freezing temperature) of leaves and the lethal temperature to 10, 50 and 90% of the plants (LT10, LT50, and LT90, respectively). Two wild-type genotypes were used (Columbia and Ler) and their mutants (esk-1 and frs-1, respectively), which differ in their freezing resistance. This study's results indicated that the mutant esk-1, described as a freezing-tolerant species showed freezing tolerance only after a cold-acclimation period. The mutant frs-1, described as freezing sensitive, presented freezing avoidance. Both wild genotypes presented LT50 similar to or higher than the ice-nucleation temperature. Thus, the main freezing-resistance mechanism for A. thaliana is avoidance of freezing by supercooling. No injury of the photosynthetic apparatus was shown by measuring the maximal photochemical efficiency (Fv/Fm) and pigments (chlorophyll and carotenoid) during cold acclimation in all genotypes. During cold acclimation, Columbia and esk-1 increased total soluble carbohydrates in leaves. esk-1 was the only genotype that presented freezing tolerance after cold acclimation. This feature could be related to an increase in sugar accumulation in the apoplast.