Escherichia coli mutants deficient in 3-methyladenine-DNA glycosylase

Two Escherichia coli K12 mutants defective in 3-methyladenine-DNA glycosylase have been isolated following mutagenesis by N-methyl-N-nitro-N-nitrosoguanidine. The mutants, which are of independent origin and have been designated tag-1 and tag-2, contain greatly reduced amounts of 3-methyladenine-DNA glycosylase activity in cell-free extracts. The defect in the tag-1 strain is observed at 43 °C but not at 30 °C, and a partially purified enzyme from this strain is unusually heat-labile, indicating that the defect in the tag-1 strain is due to a mutation in the structural gene for 3-methyladenine-DNA glycosylase.We have shown that 3-methyladenine-DNA glycosylase is responsible for the rapid removal of 3-methyladenine from the DNA of E. coli cells treated with monofunctional alkylating agents. The active release of this base is greatly impaired in the mutant strains. Both tag mutant strains are abnormally sensitive to killing by monofunctional alkylating agents and are defective in the host cell reactivation of methyl methanesulphonate-treated bacteriophage A. The tag mutation does not confer an increased sensitivity to ultraviolet or X-irradiation, and host cell reactivation of irradiated λ is normal in these strains. Further, there was no increase in the rate of spontaneous mutation in a tag strain.Three-factor transductional crosses with nalA and nrdA have shown that the tag-2 mutation is located at 47.2 minutes on the map of the E. coli K12 chromosome. In the mapping experiments, the tag-1 mutation behaved differently and appeared to be located at 43 to 46 minutes, in a closely situated but non-adjacent gene. Possible implications of the non-identity of the tag-1 and tag-2 mutations are discussed.     

A form of elongation factor G insensitive to N-ethyl-maleimide

Treatment of elongation factor G (EF-G) with the thiol reagent N-ethylmaleimide only partially inhibits (10 to 70%) the activity of the factor in (a) guanosine nucleotide·EF-G·ribosome complex formation, (b) uncoupled ribosome-dependent GTP hydrolysis, and (c) polypeptide synthesis. Moreover, a similar treatment of the factor with N-[³H]ethylmaleimide does not lead to ³H-label being associated with a GDP·EF-G·ribosome·fusidic acid complex. Thus, the results indicate the presence in EF-G preparations of a form of the factor that does not react with N-ethylmaleimide.     

β-glucanases of the yeast Pichia polymorpha

Fractionation of proteins secreted into the culture medium by intact cells and protoplasts of Pichia polymorpha showing enzyme activity against laminarin, pustulan or p-nitrophenyl--d-glucopyranoside has been performed, and the results compared with those obtained with cell-free extracts and lysed protoplasts. Fractionation with DEAE Sephadex A₅₀ has proved to be the best method, yielding at least three fractions which hydrolyse laminarin. One of these fractions was active on both laminarin and pustulan. Filtration on Sephadex G-100 column only yielded one active preparation. Evidence supporting the conclusion that there are three different -glucanases located in the periplasmic space is presented.     

Alpha detection

The problem of defining EEG alpha activity, and of detecting and measuring it, is outlined. Some advantages of a threshold method are presented and compared with an amplitude-integration method. Characteristics of percent-time scoring, based upon observable alpha spindles in the waking EEG, are discussed. A probability distribution of percent-time alpha as a function of detection threshold is derived and compared with empirical data.     

Annual phytoplankton cycle in a meromictic anoxic basin of a Rhode Island (USA) estuarine river

Hydrobiologia - Estuarine Pettaquamscutt River is a unique habitat 10 km in length with physical and biogeochemical characteristics analogous to a miniature fjord. Its meromictic upper...     

Human habituation reduces hyrax flight initiation distance in Serengeti

Many animal populations are exposed to disturbance originating from human activities. In response to human disturbance, certain animals display a variety of potentially costly behavioural responses, such as increased antipredator behaviour or relocation to new areas. In contrast, other animals seemingly thrive in the presence of humans and benefit from human-derived resources. Flight initiation distance (FID: the distance between predator and prey when prey starts to flee) is a measure commonly used to assess animals’ tolerance to humans. In this study, we tested how FID changes in relation to human presence in two hyrax species in Serengeti National Park. Hyraxes living on kopjes (rock outcrops) among human settlements showed a significantly shorter FID than hyraxes living on kopjes without human settlements. In addition, we found that hyraxes feeding before the experiment had shorter FID than hyraxes resting or being vigilant, and hyraxes disturbed during the early morning had shorter FID than hyraxes disturbed during late morning. We did not find any significant effects of group size or species composition on FID. Our results suggest that hyraxes living in the presence of humans are habituated and are not adversely affected by human settlements.     

Photodynamic inactivation of multiresistant bacteria (KPC) using zinc(II)phthalocyanines

The worldwide increase in antibiotic resistance has led to search of alternatives anti-microbial therapies such as photodynamic inactivation. The aim of this paper was to evaluate the photodynamic activity in vitro of a neutral and two cationic Zn phthalocyanines. Their photokilling activity was tested on Escherichia coli ATCC 25922 and Klebsiella pneumoniae Carbapenemase (KPC)-producing. After treating bacteria with phthalocyanines, the cultures were irradiated with white light. As a result, the bacteria were inactivated in presence of cationic phthalocyanines. The photoinactivation was dependent of the irradiation time and phthalocyanine concentration. The most effective photosensitizer on KPC-producing was Zinc(II)tetramethyltetrapyridino[2,3-b:2′,3′-g:2″,3″-l:2?,3?-q]porphyrazinium methylsulfate (ZnTM2,3PyPz). After irradiation using the water soluble ZnTM2,3PyPz (3 μM) the viability of KPC (30 min of irradiation) and E. coli (10 min of irradiation) decreased ≈99.995%.