Laura J. Fooks

Prebiotics, probiotics and human gut microbiology

Abstract Because of its resident microbiota, the human colon is one of the body’s most metabolically active organs. Gut bacteria predominantly ferment undigested food materials. The nature of the fermentation may have different health consequences. For example, the end products of carbohydrate metabolism are benign, whilst proteolytic metabolites may be toxic. The use of diet to fortify certain gut flora components is a popular current aspect of functional food sciences. In this context probiotics, prebiotics and synbiotics all have a significant role. Probiotics are live microbial additions to the diet; prebiotics are foodstuffs that have a selective metabolism in the hindgut, whilst synbiotics are combinations of the two approaches. It has been demonstrated that each of these dietary intervention routes can have an effect on the gut flora ‘balance’. Whilst the real health advantages remain elusive, the use of gut microflora management has a number of potentially very important effects with resistance to pathogens, effects on gut tumours and reduction in blood lipids holding much promise. The advent of molecular tools into gut microbiology, now offer the means to more fully explore the gut biodiversity as well as reliably track changes in response to diet. The near future will determine whether the full potential of probiotics, prebiotics and synbiotics can be realised.

Structure and biogenesis of the capsular F1 antigen from Yersinia pestis: Preserved folding energy drives fiber formation

Most gram-negative pathogens express fibrous adhesive virulence organelles that mediate targeting to the sites of infection. The F1 capsular antigen from the plague pathogen Yersinia pestis consists of linear fibers of a single subunit (Caf1) and serves as a prototype for nonpilus organelles assembled via the chaperone/usher pathway. Genetic data together with high-resolution X-ray structures corresponding to snapshots of the assembly process reveal the structural basis of fiber formation. Comparison of chaperone bound Caf1 subunit with the subunit in the fiber reveals a novel type of conformational change involving the entire hydrophobic core of the protein. The observed conformational change suggests that the chaperone traps a high-energy folding intermediate of Caf1. A model is proposed in which release of the subunit allows folding to be completed, driving fiber formation.

In vitro investigations of the effect of probiotics and prebiotics on selected human intestinal pathogens

Abstract This study investigated the effects of selected probiotic microorganisms, in combination with prebiotics, on certain human intestinal food-borne pathogens. Probiotics grown with different carbohydrate sources were observed to inhibit growth of Escherichia coli, Campylobacter jejuni and Salmonella enteritidis, with the extent of inhibition varying according to the carbohydrate source provided. Prebiotics identified as being preferentially utilised by the probiotics tested were oligofructose (FOS), inulin, xylo-oligosaccharide (XOS), and mixtures of inulin:FOS (80:20 w/w) and FOS:XOS (50:50 w/w). Two of the probiotics, Lactobacillus plantarum and Bifidobacterium bifidum were selected for further co-culture experiments. Each was combined with the selected prebiotics, and was observed to inhibit pathogen growth strongly. Results suggested that acetate and lactate were directly conferring antagonistic action, which was not necessarily related to a lowering of culture pH.

Resolving the energy paradox of chaperone/usher-mediated fibre assembly

Periplasmic chaperone/usher machineries are used for assembly of filamentous adhesion organelles of Gram-negative pathogens in a process that has been suggested to be driven by folding energy. Structures of mutant chaperone-subunit complexes revealed a final folding transition (condensation of the subunit hydrophobic core) on the release of organelle subunit from the chaperone-subunit pre-assembly complex and incorporation into the final fibre structure. However, in view of the large interface between chaperone and subunit in the pre-assembly complex and the reported stability of this complex, it is difficult to understand how final folding could release sufficient energy to drive assembly. In the present paper, we show the X-ray structure for a native chaperone-fibre complex that, together with thermodynamic data, shows that the final folding step is indeed an essential component of the assembly process. We show that completion of the hydrophobic core and incorporation into the fibre results in an exceptionally stable module, whereas the chaperone-subunit pre-assembly complex is greatly destabilized by the high-energy conformation of the bound subunit. This difference in stabilities creates a free energy potential that drives fibre formation.

Mixed culture fermentation studies on the effects of synbiotics on the human intestinal pathogens Campylobacter jejuni and Escherichia coli

Batch and continuous culture anaerobic fermentation systems, inoculated with human faeces, were utilised to investigate the antimicrobial actions of two probiotics, Lactobacillus plantarum 0407, combined with oligofructose and Bifidobacterium bifidum Bb12, combined with a mixture of oligofructose and xylo-oligosaccharides (50:50 w/w) against E. coli and Campylobacter jejuni. In batch fermenters, both E. coli and C. jejuni were inhibited by the synbiotics, even when the culture pH was maintained at around neutral. In continuous culture C. jejuni was inhibited but the synbiotic failed to inhibit E. coli. Although no definitive answer in addressing the mechanisms underlying antimicrobial activity was derived, results suggested that acetate and lactate directly were conferring antagonistic action, rather than as a result of lowering culture pH. In the course of the study culturing and fluorescent in situ hybridisation (FISH) methodologies for the enumeration of bacterial populations were compared. Bifidobacterial populations were underestimated using plating techniques, suggesting the non-culturability of certain bifidobacterial species.