Raffaella Zanchi

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.

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.

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.

Oxygen tolerance of anaerobic bacteria isolated from human feces

The large bowel intestinal flora of mammals is made up mostly of O2-intolerant anaerobic microorganisms which are irreversibly damaged by brief exposure to air. The aim of our work was to investigate the effect of atmospheric O2 on human intestinal anaerobic microorganisms. Thirty O2-intolerant bacterial strains that reached 100% mortality after 120 min of air exposure were isolated. Ten of these strains were tested for their atmospheric O2 sensitivity as a function of air exposure time; all tested microorganisms showed a similar mortality trend on exposure to air. In fact, 50% of cells survive, on the average, after 4–5 min of atmospheric O2; this percentage decreases to 3–5% after only 20 min, and after 40 min only one cell in a thousand survives; all strains reached 100% mortality in a time range of 100–120 min. The strains examined were identified as belonging to the generaEubacterium, Peptostreptococcus, andCoprococcus.

Effect ofCamellia sinensis L. whole plant extract on piglet intestinal ecosystem

The employment ofCamellia sinensis L. whole plant extract as food supplement in livestock nutrition has been suggested in order to prevent usual livestock intestinal diseases. The aim of the present research was to test the effects of such plant extract on the composition of pig faecal microbiota. Preliminaryin vitro fermentation trials evidenced in mixed pig faecal cultures, supplemented with the tested extract, an increase of total anaerobe (p=0.02) and aerobe (p=0.03) bacteria, and a decrease of clostridia (p=0.04) compared to control cultures. Afterwards we investigatedin vivo the effects on piglet faecal microbiota of a diet added with 250 mg/kg ofCamellia sinensis whole plant extract. A control diet without the plant extract, but added with antibiotic (sulphadiazine, trimethoprim, and tiamulin) was used for the comparison. Microbiological analyses of faecal samples collected after 60 days of the experimental feeding, evidenced a decrease of clostridia (p=0.001) and enterococci (p=0.04) counts in the faeces of animals fed with the experimental diet, compared to those fed with the control diet. These results show that theCamellia sinensis L. whole plant extract is able to reduce the number of some potential pathogenic bacteria in piglet gut and hence might improve animal health.

Modulation by lactic-acid bacteria of the intestinal ecosystem and plasma cholesterol in rabbits fed a casein diet

Abstract The effect of lactic acid bacteria on the serum cholesterol levels and the cecal microflora in rabbits fed dietary casein has been examined. A control group was fed a soybean protein diet, three other groups a casein diet; two of tho groups given casein were also given lyophilised resting cells of lactic acid bacteria: Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus to one group and Lactobacillus acidophilus to the other. After 42 d of the experimental diets the cecal content was subjected to microbiological analysis: there was no modification of microflora composition with regard to genera, however there were differences in cecal SCFA production and the frequency of the Bacteroides and Clostridium species. Moreover the high serum cholesterol levels found in the rabbits fed the casein diet were decreased after the administration of lactic acid bacteria, revealing the positive role of such bacteria. Our microbiological data underline the importance of diet on the growth and activity of the different bacteria species present in the intestinal ecosystem, and confirm the utility of lactic acid bacteria in restoring microflora balance.

Effects of a selection of additives on in vitro ruminal methanogenesis and in situ and in vivo NDF digestibility

The effects of 18 essential oils, yeast, Quebracho tannin and Quillaja saponin on ruminal methane and gas production (GP) were studied in vitro. A lactating cow diet was incubated with rumen inoculum. Doses of the additives (mg/L) were: essential oils = 500; tannin = 67; yeast = 8.35 and 16.7; and saponin = 300. Lemongrass, estragole, eugenol, geraniol, limonen, thyme oil and thymol produced less gas (overall mean 33.8 mL/200 mg dry matter (DM)) than control (43.6 mL/200 mg DM; P < 0.001). Methane produced (mL/200 mg DM) by guaiacol (10.7), lemongrass (9.6), limonene (11.4), thyme oil (10.9) and thymol (2.1) was lower than control (12.5) (P < 0.001). Methane percentage on total GP was lower (P < 0.001) for cinnamic alcohol (25.4), guaiacol (24.5), thymol (19.7) and vanillin (26.3) than control (28.8). In a second experiment, thymol, guaiacol and yeast were added to the diet of dry fistulated cows to determine in situ neutral detergent fiber digestibility (NDFD) of six forages and in vivo dietary NDFD. Thymol and yeast decreased in situ NDFD after 24 h (33.9% and 33.5% vs. 38.1%; P = 0.008). Thymol decreased in vivo total tract NDFD (40.8% vs. 51.4%; P = 0.02). Differences in GP and methane levels were registered within classes of additives. A careful selection of additives may allow for the manipulation of ruminal fermentation.