Enrica Canzi

Arsenic-resistant bacteria associated with roots of the wild Cirsium arvense (L.) plant from an arsenic polluted soil, and screening of potential plant growth-promoting characteristics

A rhizobacterial community, associated with the roots of wild thistle Cirsium arvense (L.) growing in an arsenic polluted soil, was studied by fluorescence in situ hybridization (FISH) analysis in conjunction with cultivation-based methods. In the bulk, rhizosphere, and rhizoplane fractions of the soil, the qualitative picture obtained by FISH analysis of the main phylogenetic bacterial groups was similar and was predominantly comprised of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. The arsenic-resistant isolates belonged to 13 genera, the most abundant being those of Bacillus, Achromobacter, Brevundimonas, Microbacterium, and Ochrobactrum. Most bacteria grew in the presence of high arsenic concentrations (over 100mM arsenate and 10mM arsenite). Most strains possessed the ArsC, ArsB and ACR3 genes homologous to arsenate reductase and to the two classes of arsenite efflux pumps, respectively, peculiar to the ars operon of the arsenic detoxification system. ArsB and ACR3 were present simultaneously in highly resistant strains. An inconsistency between 16S rRNA phylogenetic affiliations and the arsenate reductase sequences of the strains was observed, indicating possible horizontal transfer of arsenic resistance genes in the soil bacterial community. Several isolates were able to reduce arsenate and to oxidise arsenite. In particular, Ancylobacter dichloromethanicum strain As3-1b possessed both characteristics, and arsenite oxidation occurred in the strain also under chemoautotrophic conditions. Some rhizobacteria produced siderophores, indole acetic acid and 1-amino-cyclopropane-1-carboxylic acid deaminase, thus possessing potential plant growth-promoting traits.

Isolation and characterization ofMethanobrevibacter oralis sp. nov.

A new coccobacillary, nonmotile, Gram-positive, methane-producing organism was isolated from human subgingival plaque. Both hydrogen and carbon dioxide were required for growth. No methane was produced from acetate, formate, or methanol. The optimum pH was 6.9–7.4, and the optimum temperature was 36–38°C. Fecal extract was required for growth, and a volatile fatty acid mixture was highly stimulatory. The DNA G+C content was 28 mol%. On the basis of these characteristics, DNA-DNA hybridization studies, and electrophoretic analysis of cellular proteins, the isolate was considered a new species and namedMethanobrevibacter oralis.

Conditions affecting cell surface properties of human intestinal bifidobacteria

The cell surface properties of human intestinal bifidobacteria have been characterized for 30 strains isolated from a fecal sample. Strain identification to the species level was obtained by restriction analysis of the amplified 16S rRNA gene and confirmed by DNA/DNA reassociation experiments. The isolates were grouped in four genetically homogeneous clusters whose members belonged to Bifidobacterium bifidum, Bifidobacterium adolescentis, Bifidobacterium longum and Bifidobacterium pseudocatenulatum species. Cell surface properties of Bifidobacterium strains were evaluated by determining the level of hydrophobicity, adhesion to hydrocarbons and contact angle measurements, and their autoaggregation ability. The results showed high and homogeneous level of hydrophobicity in all tested strains when contact angle measurements values were considered. On the contrary, autoaggregation assays and bacterial adhesion to hydrocarbons detected interesting differences in cell surface properties among the tested Bifidobacterium strains. The highest levels of autoaggregation, detected in B. bifidum and B. adolescentis strains, were strictly dependent on the pH of the medium. Moreover, protease treatment experiments suggested that proteins had a key role in the autoaggregating ability of B. bifidum and B. adolescentis strains.

Methanogens in the human intestinal tract and oral cavity

The incidence and concentration of methanobacteria in the human intestinal tract have not been well evaluated. Only recently were such microorganisms found in the oral cavity. We determined the counts of methanogens in the feces of healthy subjects on a Mediterranean diet and evaluated whether individuals with methanobacteria in the intestine also harbor such bacteria in the oral cavity. Methanobacteria were observed in the feces of 18 of the 20 subjects, at a level ranging from 103 to 1010/g dry wt. Only 45% of the subjects harbored methanobacteria in the plaque and saliva, showing that the presence of methanogens in the oral cavity was not correlated with their presence in the feces. The presence and number of methanobacteria appeared to remain constant after 3 months. A short rod arranged in chains, similar to theMethanobrevibacter smithii which predominates in feces, was the methanogenic form present in the mouth.

Effects of a synbiotic milk product on human intestinal ecosystem

Aims:  To investigate the effect of prolonged consumption of a synbiotic milk (Synbiotic) containing Lactobacillus acidophilus (strain 74‐2, 107 CFU ml−1), Bifidobacterium lactis (strain 420, 107 CFU ml−1) and 2% inulin on colonic ecosystem in healthy humans.

Enzymatic synthesis of 12-ketoursodeoxycholic acid from dehydrocholic acid in a membrane reactor

SummaryDehydrocholic acid (3,7,12-trioxo-5β-cholanic acid) (0.5% concentration) was completely and selectively reduced to 12-ketoursodeoxycholic acid (3α, 7β-dihydroxy-12-oxo- 5β-cholanic acid) in a membrane reactor by means of 3α-hydroxysteroid dehydrogenase and 7β-hydroxysteroid dehydrogenase. Coenzyme regeneration was carried out with the glucose-glucose dehydrogenase system.

Methanogenic bacteria: presence in foodstuffs

Methanogenic bacteria are anaerobic, oxygen‐intolerant microorganisms, and it is only by studying the different habitats of such bacteria that fundamental information about their ecology becomes available. This research has evaluated methanogenic bacteria in apparently aerobic ecosystems, in foodstuffs not subjected to chemical‐physical reclamation processes, where the presence of methanogenic bacteria has never been investigated.

Influence of long-term feeding of different purified dietary fibers on the volatile fatty acid (VFA) profile, pH and fiber-degrading activity of the cecal contents in rats

Abstract The aim of this study was to investigate the effect of four weeks ingestion of 10% fiber diets (cellulose, lignocellulose, pectin or guar gum) and fiber free diets on volatile fatty acid (VFA) concentration, pH, and in vitro fiber-degrading activity of the cecal contents of female Sprague Dawley rats. The pH was significantly lower (p

Prevalence of oxygen-intolerant microorganisms in primary bile acid 7α-dehydroxylating mouse intestinal microflora

The in vitro 7α-dehydroxylation of cholic and chenodeoxycholic acids by mixed cultures of mouse cecal microorganisms was studied. Conventional anaerobic techniques and rigorous oxygen-free anaerobic experimental conditions were compared. It was found that the total number of anaerobic oxygen-intolerant microorganisms was about 10 times higher than that of anaerobic microorganisms that tolerate oxygen. Among the anaerobic 7α-dehydroxylating microorganisms, the oxygen-intolerant ones are about 1,000 to 10,000 times more numerous than the oxygen-tolerant ones. It can be concluded that the 7α-dehydroxylating activity is more common among oxygenintolerant than oxygen-tolerant anaerobic microorganisms.

Effects of Cocoa Husk Feeding on the Composition of Swine Intestinal Microbiota

A two-diet/two-period change over experiment was performed to investigate the effects of cocoa husks, as a source of dietary fiber and polyphenols, on pig intestinal microbial composition. Six pigs were fed a conventional cereal-based diet or a diet obtained by substitution of 7.5% of the conventional diet with cocoa husks for 3 weeks. Experimental diets were isoproteic and isoenergetic. At the end of each 3 week testing period, samples of fresh feces were collected and analyzed for microbial composition by fluorescence in situ hybridization. Cocoa husks did not affect feed intake, weight gain, and feed efficiency. Analysis of fecal microbial populations, grouped by phyla, showed a decrease of Firmicutes and an increase of Bacteroidetes in cocoa husk-fed pigs. Particularly, cocoa husks reduced fecal populations of the Lactobacillus-Enterococcus group and Clostridium histolyticum and increased the Bacteroides-Prevotella group and Faecalibacterium prausnitzii, suggesting a potential for cocoa husks in the improvement of intestinal microbial balance.