Dietary polyphenols are components of many foods such as tea, fruit, and vegetables and are associated with several beneficial health effects although, so far, largely based on epidemiological studies. The intact forms of complex dietary polyphenols have limited bioavailability, with low circulating levels in plasma. A major part of the polyphenols persists in the colon, where the resident microbiota produce metabolites that can undergo further metabolism upon entering systemic circulation. Unraveling the complex metabolic fate of polyphenols in this human superorganism requires joint deployment of in vitro and humanized mouse models and human intervention trials. Within these systems, the variation in diversity and functionality of the colonic microbiota can increasingly be captured by rapidly developing microbiomics and metabolomics technologies. Furthermore, metabolomics is coming to grips with the large biological variation superimposed on relatively subtle effects of dietary interventions. In particular when metabolomics is deployed in conjunction with a longitudinal study design, quantitative nutrikinetic signatures can be obtained. These signatures can be used to define nutritional phenotypes with different kinetic characteristics for the bioconversion capacity for polyphenols. Bottom-up as well as top-down approaches need to be pursued to link gut microbial diversity to functionality in nutritional phenotypes and, ultimately, to bioactivity of polyphenols. This approach will pave the way for personalization of nutrition based on gut microbial functionality of individuals or populations.polyphenol bioconversion | gut microbiota | metabolomics | metagenomics | microbiomics

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Polyphenols, ubiquitously present in the food we consume, may modify the gut microbial composition and/or activity, and moreover, may be converted by the colonic microbiota to bioactive compounds that influence host health. The polyphenol content of fruit and vegetables and derived products is implicated in some of the health benefits bestowed on eating fruit and vegetables. Elucidating the mechanisms behind polyphenol metabolism is an important step in understanding their health effects. Yet, this is no trivial assignment due to the diversity encountered in both polyphenols and the gut microbial composition, which is further confounded by the interactions with the host. Only a limited number of studies have investigated the impact of dietary polyphenols on the complex human gut microbiota and these were mainly focused on single polyphenol molecules and selected bacterial populations. Our knowledge of gut microbial genes and pathways for polyphenol bioconversion and interactions is poor. Application of specific in vitro or in vivo models mimicking the human gut environment is required to analyse these diverse interactions. A particular benefit can now be gained from next-generation analytical tools such as metagenomics and metatranscriptomics allowing a wider, more holistic approach to the analysis of polyphenol metabolism. Understanding the polyphenol–gut microbiota interactions and gut microbial bioconversion capacity will facilitate studies on bioavailability of polyphenols in the host, provide more insight into the health effects of polyphenols and potentially open avenues for modulation of polyphenol bioactivity for host health.

Two novel antibacterial peptides of clostridial species were purified, N-terminally sequenced, and characterized. Moreover, their structural genes were identified. Closticin 574 is an 82-amino-acid bacteriocin produced by Clostridium tyrobutyricum ADRIAT 932. The supernatant of the producing strain showed a high level of activity against the indicator strain C. tyrobutyricum. The protein is synthesized as a preproprotein that is possibly secreted via the general secretion pathway, after which it is hydrolyzed at an Asp-Pro site. Circularin A is produced by Clostridium beijerinckii ATCC 25752 as a prepeptide of 72 amino acids. Cleavage of the prepeptide between the third leucine and fourth valine residues followed by a head-to-tail ligation between the N and C termini creates a circular antimicrobial peptide of 69 amino acids. The unusually small circularin A leader peptide of three amino acids is cleaved off in this process. The supernatant of C. beijerinckii ATCC 25752 showed a broad antibacterial activity range.Clostridia have a negative image as many species are known as pathogens (50), toxin producers (50), and food-spoilage bacteria (36). Various clostridia produce bacteriocins, but despite their long history as a means of typing clostridia (33, 39), only little sequence, functional, or structural information is available on these antibacterial peptides. The few clostridial bacteriocins that have been further characterized are BCN5 and boticin B (12, 18). BCN5 is a large (97-kDa) UV-inducible protein produced by Clostridium perfringens (18). Boticin B is produced by Clostridium botulinum as a small peptide with a predicted size of 50 amino acid residues (12). Little is known about the regulation of production or secretion of these bacteriocins. Generally, bacteriocins are small ribosomally synthesized antimicrobial peptides (27,35). They are mostly membrane permeabilizing and cationic, and they typically comprise fewer than 50 amino acid residues (35). Bacteriocins can be used as an additive to food products to prevent the growth of spoilage bacteria (10). Klaenhammer divided bacteriocins into four classes (35). Class I bacteriocins, known as lantibiotics, contain posttranslationally modified residues such as lanthionine, ␤-methyl lanthionine, and dehydrated residues. Class II bacteriocins lack these modifications and are linear peptides (35,44). Class III contains the large, heat-labile bacteriocins. Class IV bacteriocins are complex molecules composed of protein and chemical moieties. Both class I and class II bacteriocins have been intensively studied, and more than 20 and 100 representatives are known, respectively.The subclass IIc (class II bacteriocins other than the pediocin-like bacteriocins or the two-peptide bacteriocins) contains a few examples of bacteriocins that are produced as circular molecules. This circularization is the result of a head-to-tail peptide bond formation of a prepeptide. Bacteriocins with this typical structure are microcin J25, gassericin A, and AS-48/ Bac21 (6,31,40,59). Mi...