Genetic exchanges constitute a significant means by which bacteriophages acquire novel characteristics. Phages of Lactococcus lactis occupy a particular niche, the dairy factory environment, where their populations are subjected to constant changes. Little is known about the mechanisms of evolution that lead to the genetic diversity of lactococcal phages. In this study, we described two DNA exchanges involving the lytic phage ul36, a member of the P335 species, and its L. lactis host. They occurred by homologous recombination with phage-related sequences present in the host chromosome. Both mutants generated by these recombination events are insensitive to the phage resistance mechanism AbiK and one has a reduced burst size as well as a new origin of replication. We propose that this type of DNA exchange with prophages or remnants of prophages occurs frequently within the P335 species as supported by DNA-DNA comparisons between P335-like phages.

Lactococcal phage mutants insensitive to the antiviral abortive infection mechanism AbiK are divided into two classes. One comprises virulent phages that result from DNA exchanges between a virulent phage and the host chromosome. Here, we report the analysis of the second class of phage mutants, which are insensitive to AbiK as a result of a single nucleotide change causing an amino acid substitution. The mutated genes occupy the same position in the various lactococcal phage genomes, but the deduced proteins do not share amino acid sequence similarity. Four nonsimilar proteins involved in the sensitivity to AbiK (Sak) were identified. Two of these Sak proteins are related to Erf and RAD52, single-strand annealing proteins involved in homologous recombination.Lactococcus lactis strains used in the manufacture of fermented dairy products are susceptible to infection by virulent bacteriophages, which can interrupt the fermentation process. Members of three genetically distinct lactococcal phage groups are repeatedly isolated from unsuccessful dairy fermentations, namely species 936, c2, and P335 (18). Bacteria are also known to possess defense barriers against phage infection. More than 50 natural L. lactis phage resistance systems have been characterized, and they are divided into four groups according to the time at which they act during the lytic cycle (10). They include the inhibition of phage adsorption, blocking of DNA ejection, restriction and modification systems, and abortive infection mechanisms (Abi) (10). The Abi systems form a heterogeneous group that includes all cell defenses that act after DNA ejection into the cytoplasm and lead to cell death (10). To date, over 20 distinct Abi systems have been cloned and sequenced in Lactococcus, but little is known about the molecular mechanisms used by Abi proteins to block phage infection.Two general types of phage mutants can be obtained through the selective pressure of Abi systems. The first class is obtained only with P335-like phages, and these mutants result from homologous recombination with phage-related sequences present in the host chromosome (5,6,11,12,21). To date, these recombination mutants have been isolated during the study of AbiA, AbiC, AbiK, and AbiT only. The second class is found in members of the three groups, and these phages carry only point mutations. Their characterization led to the identification of phage elements that are involved in the sensitivity to lactococcal Abi systems. Two AbiA-insensitive derivatives of phage 31 (species P335) bearing point mutations have been characterized, and the presence of the mutated intergenic region or orf245 of the bacteriophage reduced the efficacy of AbiA (11). On the other hand, the efficacy of AbiD1 was increased by the expression of the wild-type orf1 of phage bIL66 (species 936) (3). AbiK-insensitive class I phage mutants have been characterized previously (6). Here, 10 AbiK-insensitive class II phage derivatives were isolated and analyzed.Isolation and characterization of AbiK-insensitive ...

Abortive infection mechanisms of

Objectives: To determine the association between risk of rheumatoid arthritis (RA) and alcohol consumption in combination with smoking and HLA-DRB1 shared epitope (SE). Methods: Data from two independent case-control studies of RA, the Swedish EIRA (1204 cases and 871 controls) and the Danish CACORA (444 cases and 533 controls), were used to estimate ORs of developing RA for different amounts of alcohol consumed. Results: Alcohol consumption was significantly more common in controls (p,0.05) and dose-dependently associated with reduced risk of RA (p for trend ,0.001) in both studies. Among alcohol consumers, the quarter with the highest consumption had a decreased risk of RA of the order of 40-50% compared with the half with the lowest consumption (EIRA, OR = 0.5 (95% CI 0.4 to 0.6); CACORA, OR = 0.6 (95% CI 0.4 to 0.9)). For the subset of RA that is seropositive for antibodies to citrullinated peptide antigens, alcohol consumption reduced the risk most in smokers carrying HLA-DRB1 SE alleles. Conclusions: The observed inverse association between alcohol intake and risk of RA and the recent demonstration of a preventive effect of alcohol in experimental arthritis indicate that alcohol may protect against RA. This highlights the potential role of lifestyle in determining the risk of developing RA, and emphasises the advice to stop smoking, but not necessarily to abstain from alcohol in order to diminish risk of RA. The evidence of potential RA prevention should prompt additional studies on how this can be achieved.Rheumatoid arthritis (RA) is a common, complex disease which seems to develop as a result of an interplay between inducing and protective environmental and genetic factors. [1][2][3][4][5] Recently, evidence for a possible interaction between lifestyle factors and genetic factors was provided by studies showing how smoking interacts with the shared epitope (SE) alleles of the HLA-DRB1 gene in providing a very high risk of developing RA. Furthermore, the effect of both these risk factors was confined to one subset of RA, characterised by the presence of antibodies to citrullinated peptide antigens (ACPAs).2-4 6 These findings are of interest not only for public health, but also from a biological perspective, as they provide leads to a possible aetiology of RA.2 In a more general sense, they illustrate how investigations of lifestyle factors can benefit from being performed in the context of genetics, after appropriate subdivision of the disease into subsets.Our interest in the role of alcohol consumption was triggered by several reports suggesting that alcohol influences inflammation in general and arthritis in particular; alcohol has been shown to diminish the response to immunogens in animals as well as in humans.7-10 Alcohol can downregulate the production of proinflammatory molecules through its influence on innate immunity. 11Notably, addition of alcohol to the drinking water of mice was recently shown to reduce clinical signs of arthritis as well as joint destruction.12 An indication that ...

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