Species-specific FISH analysis of cecal microflora in rats administered with lactic acid bacteria

Analysis of caecal microbiota in rats fed with genetically modified rice by real-time quantitative PCR

The effect of genetically modified rice (GMR) on bacterial communities in caecal content was analyzed in a 90-d feeding rat model. A total of 12 groups of rats, which included male and female, were fed with the basal diets containing 30%, 50%, 70% GMR (B(1), B(2), B(3)) or 30%, 50%, 70% non-GMR (D(1), D(2), D(3)). The structure of intestinal microflora was estimated by real-time quantitative PCR (RQ-PCR) based on genus-specific 16s rDNA primers. SYBR Green was used for accurate detection and quantification of 6 kinds of major bacteria shared by humans and rats. According to RQ-PCR, the genome copies of Lactobacillus group from the cecum of male rats fed with 70% non-GMR was higher than those fed with 70% GMR and the relative abundance of Lactobacillus group also higher for group D. This result was in contrast with the E. coli subgroup, which was more numerous in proportion of group B, except D(2) and B(2) for male rats. The Clostridium perfringens subgroup was numerically more abundant in group D than group B of the same level, also except D(2) and B(2) for male rats. These results suggested that GMR had a complex effect on caecal microflora that may be related to the health of the host.

FISH analysis of Lactobacillus biofilms in the gastrointestinal tract of different hosts

AIMS

To investigate the spatial organization of endogenous and exogenously applied Lactobacillus communities at specific locations in the adult gastrointestinal tract of different hosts.

METHODS AND RESULTS

Samples of the human, murine and avian gastrointestinal tract of subjects that received or not received a Lactobacillus probiotic were analysed by fluorescence in situ hybridization (FISH) with rRNA-targeted probes. High levels of endogenous lactobacilli were observed on the nonsecretory, stratified squamous epithelia present in the forestomach of mice and crop of chickens, respectively. These epithelial associations showed characteristics of bacterial biofilms, i.e. bacteria attached to a surface and embedded in a matrix of extracellular polymeric substances. In other regions of the analysed intestines, lactobacilli seemed to occur mainly as dispersed bacterial cells or as microcolonies. Exogenous administration of a Lactobacillus probiotic did increase the levels of loosely adherent Lactobacillus cells detected. However, the probiotic strains were unable to establish themselves inside the gastrointestinal biofilms.

CONCLUSIONS

Gastrointestinal biofilms of lactobacilli occur only in specific niches in certain hosts, such as the murine forestomach and avian crop.

SIGNIFICANCE AND IMPACT OF THE STUDY

Biofilm formation by lactobacilli in specific parts of animal gastrointestinal tracts was documented for the first time by FISH.

Racemization of l-lactic acid in pH-swing open fermentation of kitchen refuse by selective proliferation of Lactobacillus plantarum

We have shown that stable lactic acid fermentation of model kitchen refuse occurs with intermittent pH adjustment under nonsterilized conditions. Nonetheless, the optical activity of the accumulated lactic acid was low, which is disadvantageous for the production of high-quality poly-l-lactic acid. Here, we attempt to increase optical purity by introducing l-lactic acid-producing strains under nonsterilized conditions and demonstrate that the inoculation of Lactobacillus rhamnosus or Lactococcus lactis, both of which are l-lactic acid producers, is partially effective in the early fermentation stage, but does not improve the final optical purity of the accumulated lactic acid. We confirmed by fluorescence in situ hybridization using group-specific and species-specific 16S rDNA probes that this is due to the selective proliferation of naturally existing L. plantarum. L. plantarum KY-1, which is isolated from model kitchen refuse, showing lactic acid racemase activity, as well as d-lactate dehydrogenase activity, in its membrane fraction. We conclude that racemase activity associated with L. plantarum is the main cause of decreased optical purity in the accumulated lactic acid.