Microbial population dynamics in the faeces of wood-eating loricariid catfishes.

UNLABELLED: Catfishes of the genus Panaque are known for their ability to feed on wood and hence to process cellulose fibres in their digestive systems. The paper industry uses cellulose fibres and thus has an interest in exploiting this property biomimetically: it could be employed as a pretreatment to lessen the energy required by the mechanical production stage of manufacturing nanocellulose fibres. Here, we characterize the diet-associated in situ microbial diversity and population dynamic in the faeces of catfish (Panaque sp.) exposed to consecutive diets of pellet food and then wood. Fish faeces samples were collected and investigated by parallel DNA deep amplicon sequencing of the bacterial 16S rRNA SSU for both diet conditions. The most frequently occurring bacterium in the faeces was Cetobacterium sp. The dominant cellulolytic bacterial genera found in ascending relative abundance were as follows: Aeromonas sp., Flavobacterium sp., Bacteroides sp., Pseudomonas sp. and Cellvibrio sp. Diet-associated changes in the faeces microbiome were noted for Flavobacterium sp. Extensive microbial diversity was found in catfish faeces, evidenced using culture-independent molecular techniques. No significant diet-associated effects on the microbiome in terms of biodiversity were observed in the catfish faeces, but diet-associated changes in the microbial population structure were observed. SIGNIFICANCE AND IMPACT OF THE STUDY: Although catfishes are not classified as true xylivores, inhabiting their faeces are bacteria that may provide a novel source of cellulolytic enzyme. Based on this first microbiology study, the faeces and thus the gastrointestinal microbiome of Panaque catfishes are an unexplored reservoir of microbial extracts with enhanced polysaccharide transforming enzyme activity. The biomimetical exploitation of this cellulolytic activity in the form of novel enzymes or by applying a mixture of cellulolytic micro-organisms could accomplish a pretreatment to the mechanical production process of nanocellulose fibres, thus could reduce the energy consumption costs significantly.

Molecular detection of bacteria in calcium carbonate powder used in cosmetic formulations.

Given that a variety of bacterial species may occur in the calcium carbonate powder used for cosmetic formulations, an understanding of their diversity and abundance is necessary to accurately assess the contamination of the finished product. 16S rRNA was PCR-amplified from genomic DNA extracted from three different calcium carbonate powder grades, and these amplicon libraries were sequenced using deep amplicon sequencing technology. The resulting libraries contained 4149-6688 16S rRNA reads per sample with a length of 327-342 bp. Classification into genus of pyrosequencing reads of the dominant bacterial species found in calcium carbonate powders was used to confirm the absence of Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella spp. and Escherichia coli. The analysis described here can be used to determine the microbial diversity of calcium carbonate powder or the presence of any 'indicator microorganisms' in raw materials as well as in cosmetic products. This work provides guidance for prioritizing subsequent culturable and quantitative analysis, ensuring that potentially significant microorganisms are not left out of risk estimations.