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Characterization of Bacterial Communities in Feces from Healthy Elderly Volunteers and Hospitalized Elderly Patients by Using Real-Time PCR and Effects of Antibiotic Treatment on the Fecal Microbiota. Sabine Bartosch, 2004.Fecal bacteria were studied in healthy elderly volunteers (age, 63 to 90 years; n = 35) living in the local community, elderly hospitalized patients (age, 66 to 103; n = 38), and elderly hospitalized patients receiving antibiotic treatment (age, 65 to 100; n = 21) . Group- and species-specific primer sets targeting 16S rRNA genes were used to quantitate intestinal bacteria by using DNA extracted from feces and real-time PCR . The principal difference between healthy elderly volunteers and both patient cohorts was a marked reduction in the Bacteroides-Prevotella group following hospitalization . Reductions in bifidobacteria, Desulfovibrio spp., Clostridium clostridiiforme, and Faecalibacterium prausnitzii were also found in the hospitalized patients . However, total 16S rRNA gene copy numbers (per gram of wet weight of feces) were generally lower in the stool samples of the two groups of hospitalized patients compared to the number in the stool samples of elderly volunteers living in the community, so the relative abundance (percentage of the group- and species-specific rRNA gene copies in relation to total bacterial rRNA gene copies) of bifidobacteria, Desulfovibrio spp., C . clostridiiforme, and F . prausnitzii did not change . Antibiotic treatment resulted in further reductions in the numbers of bacteria and their prevalence and, in some patients, complete elimination of certain bacterial communities . Conversely, the numbers of enterobacteria increased in the hospitalized patients who did not receive antibiotics, and due to profound changes in fecal microbiotas during antibiotic treatment, the opportunistic species Enterococcus faecalis proliferated . nblS, a Gene Involved in Controlling Photosynthesis-Related Gene Expression during High Light and Nutrient Stress inSynechococcus elongatus PCC 7942. Lorraine G. van Waasbergen, 2002.The HliA protein of the cyanobacterium Synechococcus elongatus PCC 7942 is a small, thylakoid-associated protein that appears to play a role in photoprotection; its transcript rapidly accumulates in response to high-intensity light (HL) and the hli gene family is required for survival of cells in high light . In order to discover regulatory factors involved in HL acclimation in cyanobacteria, a screen was performed for chemically generated mutants unable to properly control expression of the hliA gene in response to HL . One such mutant was identified, and complementation analysis led to the identification of the affected gene, designated nblS . Based on its deduced protein sequence, NblS appears to be a membrane-bound, PAS-domain-bearing, sensor histidine kinase of two-component regulatory systems in bacteria . The nblS mutant was unable to properly control light intensity-mediated expression of several other photosynthesis-related genes, including all three psbA genes and the cpcBA genes . The mutant was also unable to control expression of the hliA and psbA genes in response to low-intensity blue/UV-A light, a response that may be related to the HL-mediated regulation of the genes . Additionally, in response to nutrient deprivation, the nblS mutant was unable to properly control accumulation of the nblA transcript and associated degradation of the light-harvesting phycobilisomes . The nblS mutant dies more rapidly than wild-type cells following exposure to HL or nutrient deprivation, likely due to its inability to properly acclimate to these stress conditions . Thus, the NblS protein is involved in the control of a number of processes critical for altering the photosynthetic apparatus in response to both HL and nutrient stress conditions .
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