Acid mine drainage of the Carnoulès mine (France) is characterized by acid waters containing high concentrations of arsenic and iron. In the first 30 m along the Reigous, a small creek draining the site, more than 38% of the dissolved arsenic was removed by co-precipitation with Fe(III), in agreement with previous studies, which suggest a role of microbial activities in the co-precipitation of As(III) and As(V) with Fe(III) and sulfate. To investigate how this particular ecosystem functions, the bacterial community was characterized in water and sediments by 16S rRNA encoding gene library analysis. Based on the results obtained using a metaproteomic approach on sediments combined with high-sensitivity HPLC-chip spectrometry, several GroEL orthologs expressed by the community were characterized, and the active members of the prokaryotic community inhabiting the creek sediments were identified. Many of these bacteria are β-proteobacteria such as Gallionella and Thiomonas, but γ-proteobacteria such as Acidithiobacillus ferrooxidans and α-proteobacteria such as Acidiphilium, Actinobacteria, and Firmicutes were also detected.

Although some of the effects of clay ingestion by humans and animals, such as gastrointestinal wellness and the increase in food efficiency are well known, the underlying mechanisms are not yet fully understood. Therefore, the interactions between the intestinal mucosa and kaolinite particles and their effects on mucosal morphology were observed using light microscopy (LM), transmission electron microscopy (TEM), conventional (CSEM) and environmental (ESEM) scanning electron microscopy combined with an EDX micro-analysis system. Kaolinite consumption, given with free access to rats, varied considerably from one animal to the other but was regular through time for each individual. Some kaolinite particles appeared chemically dissociated in the lumen and within the mucus barrier. Aluminium (Al) originating from ingested clay and present in the mucus layer could directly cross the intestinal mucosa. A significant increase in the thickness of the villi with large vacuoles at the base of the mucosal cells and a decrease in the length of enterocyte microvilli characterized complemented animals. The proteomic analyses of the intestinal mucosa of complemented rats also revealed several modifications in the expression level of cytoskeleton proteins. In summary, kaolinite particles ingested as food complement interact with the intestinal mucosa and modify nutrient absorption. However, these data, together with the potential neurotoxicity of Al, need further investigation.

Geophagia is found in various animal species and in humans. We have previously shown that spontaneously ingested kaolinite interacts with the intestinal mucosa modifies nutrient absorption and slows down gastric emptying and intestinal transit in rats in vivo. However, the precise mechanisms involved are not elucidated. The aim of this work was to investigate the effects of controlled kaolinite ingestion on food intake, gut morphology and in vitro motility in rats. Male Wistar rats were fed with 5% kaolinite in standard food pellets during 7, 14 and 28 days. Body mass and food consumption were measured daily. Intestinal morphological and proteomic analyses were conducted. The length of mucosal lacteals was evaluated. Plasmatic levels of leptin and adiponectin were determined. Finally, organ bath studies were conducted to evaluate smooth muscle contractility. Food consumption was significantly increased during the first two weeks of kaolinite ingestion without any mass gain compared to controls. Kaolinite induced weak variations in proteins that are involved in various biological processes. Compared to control animals, the length of intestinal lacteals was significantly reduced in kaolinite group whatever the duration of the experiment. Leptin and adiponectin plasmatic levels were significantly increased after 14 days of kaolinite consumption. Changes in spontaneous motility and responses to electrical nerve stimulation of the jejunum and proximal colon were observed at day 14. Altogether, the present data give evidence for a modulation by kaolinite-controlled ingestion on satiety and anorexigenic signals as well as on intestinal and colonic motility.