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The AcrAB-TolC Pump Is Involved in Macrolide Resistance but Not in Telithromycin Efflux in Enterobacter aerogenes and Escherichia coli. Renaud Chollet, 2004.The role of the AcrAB-TolC pump in macrolide and ketolide susceptibility in Escherichia coli and Enterobacter aerogenes was studied . Efflux pump inhibitor restored erythromycin, clarithromycin, and telithromycin susceptibilities to multidrug-resistant isolates . No modification of telithromycin accumulation was detected in E . aerogenes acrAB or tolC derivatives compared to that in the parental strain . Two independent efflux pumps, inhibited by phenylalanine arginine ß-naphthylamide, expel macrolides and telithromycin in E . aerogenes . Mining the Microbiota of the Neonatal Gastrointestinal Tract for Conjugated Linoleic Acid-Producing Bifidobacteria. E. Rosberg-Cody, 2004.This study was designed to isolate different strains of the genus Bifidobacterium from the fecal material of neonates and to assess their ability to produce the cis-9, trans-11 conjugated linoleic acid (CLA) isomer from free linoleic acid . Fecal material was collected from 24 neonates aged between 3 days and 2 months in a neonatal unit (Erinville Hospital, Cork, Ireland) . A total of 46 isolates from six neonates were confirmed to be Bifidobacterium species based on a combination of the fructose-6-phosphate phosphoketolase assay, RAPD [random(ly) amplified polymorphic DNA] PCR, pulsed-field gel electrophoresis (PFGE), and partial 16S ribosomal DNA sequencing . Interestingly, only 1 of the 11 neonates that had received antibiotic treatment produced bifidobacteria . PFGE after genomic digestion with the restriction enzyme XbaI demonstrated that the bifidobacteria population displayed considerable genomic diversity among the neonates, with each containing between one and five dominant strains, whereas 11 different macro restriction patterns were obtained . In only one case did a single strain appear in two neonates . All genetically distinct strains were then screened for CLA production after 72 h of incubation with 0.5 mg of free linoleic acid ml–1 by using gas-liquid chromatography . The most efficient producers belonged to the species Bifidobacterium breve, of which two different strains converted 29 and 27% of the free linoleic acid to the cis-9, trans-11 isomer per microgram of dry cells, respectively . In addition, a strain of Bifidobacterium bifidum showed a conversion rate of 18%/µg dry cells . The ability of some Bifidobacterium strains to produce CLA could be another human health-promoting property linked to members of the genus, given that this metabolite has demonstrated anticarcinogenic activity in vitro and in vivo . The Protein Encoded at the 3' End of the Serine Protease Gene of Aeromonas sobria Functions as a Chaperone in the Production of the Protease. Tomohiko Nomura, 2002.For the successful production of Aeromonas sobria serine protease (ASP), open reading frame 2 (ORF2) protein, encoded at the 3' end of the protease operon, is required . In this study, we examined the action of ORF2 protein . The results showed that the protein associated with ASP in the periplasm and helped ASP to form an active structure . Chromosomal Arm Replacement in Streptomyces griseus. Tetsuya Uchida, 2003.UV irradiation of Streptomyces griseus 2247 yielded a new chromosomal deletion mutant, MM9 . Restriction and sequencing analysis revealed that homologous recombination between two similar lipoprotein-like open reading frames, which are located 450 and 250 kb from the left and right ends, respectively, caused chromosomal arm replacement . As a result, new 450-kb terminal inverted repeats (TIRs) were formed in place of the original 24-kb TIRs . Frequent homologous recombinations in Streptomyces strains suggest that telomere deletions can usually be repaired by recombinational DNA repair functioning between the intact and deleted TIR sequences on the same chromosome . Influences of Pond Geochemistry, Temperature, and Freeze-Thaw on Terminal Anaerobic Processes Occurring in Sediments of Six Ponds of the McMurdo Ice Shelf, near Bratina Island, Antarctica. Douglas O. Mountfort, 2003.The effects of freeze-thaw, freezing and sediment geochemistry on terminal anaerobic processes occurring in sediments taken from below cyanobacterial mats in meltwater ponds of the McMurdo Ice Shelf in Antarctica were investigated . Depending on the geochemical and physical status of the sediments (i.e., frozen or thawed), as well as passage of sediment through a freeze-thaw cycle, terminal carbon and electron flow shifted in which the proportions of hydrogen and acetate utilized for methanogenesis and sulfate reduction changed . Thus, in low-sulfate (or chloride) sediment which was thawed and incubated at 4°C, total carbon and electron flow were mediated by acetate-driven sulfate reduction and H2-driven methanogenesis . When the same sediments were incubated frozen, both methanogenesis and sulfate reduction decreased . However, under these conditions methanogenesis was favored over sulfate reduction, and carbon flow from acetate to methane increased relative to sulfate reduction; >70% of methane was contributed by acetate, and more than 80% of acetate was oxidized by pathways not coupled to sulfate reduction . In high-sulfate pond sediments, sulfate reduction was a major process mediating terminal carbon and electron flow in both unfrozen and frozen incubations . However, as with low-sulfate sediments, acetate oxidation became uncoupled from sulfate reduction with freezing . Geochemical and temperature effects could be expressed by linear models in which the log (methanogenesis to sulfate reduction) was negative log linear with respect to either temperature or the log of the sulfate (or chloride) concentration . From these relationships it was possible to predict the ratio for a given temperature (low-sulfate sediments) or sulfate (chloride) concentration . Small transitory changes, such as elevated sulfate reduction coupled to increased acetate turnover, resulted from application of a freeze-thaw cycle to low-salinity pond sediments . The results demonstrate how ecophysiological processes may change in anaerobic systems under extreme conditions (e.g., freezing) and provide new insights into microbial events occurring under these conditions .
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