Isolation of Acetobacterium sp. strain AG, which reductively debrominates octa- and pentabrominated diphenyl ether technical mixtures.

Polybrominated diphenyl ethers (PBDEs) are a class of environmental pollutants that have been classified as persistent organic pollutants since 2009. In this study, a sediment-free enrichment culture (culture G) was found to reductively debrominate octa- and penta-BDE technical mixtures to less-brominated congeners (tetra-, tri-, and di-BDEs) via a para-dominant debromination pattern for the former and a strict para debromination pattern for the latter. Culture G could debrominate 96% of 280 nM PBDEs in an octa-BDE mixture to primarily tetra-BDEs in 21 weeks. Continuous transferring of culture G with octa-/penta-BDEs dissolved in n-nonane or trichloroethene (TCE) yielded two strains (Acetobacterium sp. strain AG and Dehalococcoides sp. strain DG) that retained debromination capabilities. In the presence of lactate but without TCE, strain AG could cometabolically debrominate 75% of 275 nM PBDEs in a penta-BDE mixture in 33 days. Strain AG shows 99% identity to its closest relative, Acetobacterium malicum. In contrast to strain AG, strain DG debrominated PBDEs only in the presence of TCE. In addition, 18 out of 19 unknown PBDE debromination products were successfully identified from octa- and penta-BDE mixtures and revealed, for the first time, a comprehensive microbial PBDE debromination pathway. As an acetogenic autotroph that rapidly debrominates octa- and penta-BDE technical mixtures, Acetobacterium sp. strain AG adds to the still-limited understanding of PBDE debromination by microorganisms.

Identification and transcriptional analysis of trans-DCE-producing reductive dehalogenases in Dehalococcoides species.

During microbial reductive dechlorination of tetrachloroethene (PCE) and trichloroethene (TCE), trans-1, 2-dichloroethene (trans-DCE) has been observed to be produced predominantly by certain mixed and pure cultures. However, the reductive dehalogenase (RDase) genes involved in trans-DCE generation remain elusive. In this study, identification and transcriptional analysis of RDases were conducted on trans-DCE-producing Dehalococcoides sp. strain MB. Two pairs of degenerate primers targeting the conserved regions of RDases in known Dehalococcoides species were applied to amplify the putative RDase genes of strain MB. Cloning and restriction analysis revealed the presence of seven unique RDase gene fragments (dceA1 to dceA7) that possess sequence identity to known RDase genes. Gene expression analysis of the PCE-grown culture MB exhibited 10-fold regulation of the RDase gene dceA6 (designated mbrA gene), suggesting that it is involved in the production of trans-DCE. This is in agreement with the molecular size of the most abundant protein that is resolved on the denaturing protein gel. Complete sequence of the mbrA gene was obtained by chromosome walking, and the upstream of it is a regulator of transcription, indicating that the expression of this functional gene is tightly controlled in the microbe. The mbrA gene was subsequently found to be present in other trans-DCE-producing cultures containing Dehalococcoides sp. The new mbrA gene identified in this study may serve as an important biomarker for evaluating, predicting and elucidating the biological production of trans-DCE in the chloroethene-contaminated sites.

A Dehalococcoides-containing co-culture that dechlorinates tetrachloroethene to trans-1,2-dichloroethene.

In the microbial reductive dechlorination of tetrachloroethene (PCE) and trichloroethene (TCE), dechlorinators usually produce cis-1,2-dichloroethene (cis-DCE) as the predominant product or an intermediate. This study shows that dechlorination of PCE and TCE can also lead to the generation of trans-1,2-dichloroethene (trans-DCE) by a co-culture MB. During its enrichment process, the ratio of trans- to cis-DCE increased from 1.4 (+/-0.1):1-3.7 (+/-0.4):1, whereas the TCE reductive dechlorination rate went up from approximately 26.2 to approximately 68.8 micromol l(-1) day(-1). PCR-denaturing gradient gel electrophoresis (PCR-DGGE) revealed that the increased ratio of trans- /cis-DCE was well correlated with the increased proportions of Dehalococcoides and the disappearance of Desulfuromonas during the enrichment process. As shown by PCR-DGGE, similar Dehalococcoides species were consistently present in another three sediment-free cultures with various trans- /cis-DCE ratios. The 16S rRNA gene sequence of this Dehalococcoides sp. in co-culture MB is 100% identical (over 1489 bp) to that of Dehalococcoides ethenogenes strain 195 (CP000027), which belongs to the Cornell subgroup of the Dehalococcoides cluster. The other bacterium in this co-culture MB was a Sedimentibacter species, which showed no PCE or TCE dechlorination activity. Results from this study show that microbial dechlorination of chloroethenes by this particular subgroup of Dehalococcoides could result in significant accumulation of trans-DCE in the environment if no trans-DCE dechlorinators coexist in the contaminated sites.

Infant intestinal Enterococcus faecalis down-regulates inflammatory responses in human intestinal cell lines.

AIM: To investigate the ability of Lactic acid bacteria (LAB) to modulate inflammatory reaction in human intestinal cell lines (Caco-2, HT-29 and HCT116). Different strains of LAB isolated from new born infants and fermented milk, together with the strains obtained from culture collections were tested. METHODS: LABs were treated with human intestinal cell lines. ELISA was used to detect IL-8 and TGF-beta protein secretion. Cytokines and Toll like receptors (TLRs) gene expression were assessed using RT-PCR. Conditional medium, sonicated bacteria and UV killed bacteria were used to find the effecter molecules on the bacteria. Carbohydrate oxidation and protein digestion were applied to figure out the molecules' residues. Adhesion assays were further carried out. RESULTS: It was found that Enterococcus faecalis is the main immune modulator among the LABs by downregulation of IL-8 secretion and upregulation of TGF-beta. Strikingly, the effect was only observed in four strains of E. faecalis out of the 27 isolated and tested. This implies strain dependent immunomodulation in the host. In addition, E. faecalis may regulate inflammatory responses through TLR3, TLR4, TLR9 and TRAF6. Carbohydrates on the bacterial cell surface are involved in both its adhesion to intestinal cells and regulation of inflammatory responses in the host. CONCLUSION: These data provide a case for the modulation of intestinal mucosal immunity in which specific strains of E. faecalis have uniquely evolved to maintain colonic homeostasis and regulate inflammatory responses.

Free fucose is a danger signal to human intestinal epithelial cells.

Fucose is present in foods, and it is a major component of human mucin glycoproteins and glycolipids. l-Fucose can also be found at the terminal position of many cell-surface oligosaccharide ligands that mediate cell-recognition and adhesion-signalling pathways. Mucin fucose can be released through the hydrolytic activity of pathogens and indigenous bacteria, leading to the release of free fucose into the intestinal lumen. The immunomodulating effects of free fucose on intestinal epithelial cells (enterocyte-like Caco-2) were investigated. It was found that the presence of l-fucose up regulated genes and secretion of their encoded proteins that are involved in both the innate and adaptive immune responses, possibly via the toll-like receptor-2 signalling pathway. These include TNFSF5, TNFSF7, TNF-alpha, IL12, IL17 and IL18. Besides modulating immune reactions in differentiated Caco-2 cells, fucose induced a set of cytokine genes that are involved in the development and proliferation of immune cells. These include the bone morphogenetic proteins (BMP) BMP2, BMP4, IL5, thrombopoietin and erythropoietin. In addition, the up regulated gene expression of fibroblast growth factor-2 may help to promote epithelial cell restitution in conjunction with the enhanced expression of transforming growth factor-beta mRNA. Since the exogenous fucose was not metabolised by the differentiated Caco-2 cells as a carbon source, the reactions elicited were suggested to be a result of the direct interaction of fucose and differentiated Caco-2 cells. The presence of free fucose may signal the invasion of mucin-hydrolysing microbial cells and breakage of the mucosal barrier. The intestinal epithelial cells respond by up regulation and secretion of cytokines, pre-empting the actual invasion of pathogens.