The Shine-Dalarno (SD) sequence is a key element directing the translation to initiate at the authentic start codons and also enabling translation initiation to proceed in 5' untranslated mRNA regions (5'-UTRs) containing moderately strong secondary structures. Bioinformatic analysis of almost forty genomes from the major bacterial phylum Bacteroidetes revealed, however, a general absence of SD sequence, drop in GC content and consequently reduced tendency to form secondary structures in 5'-UTRs. The experimentsusing the Prevotella bryantii TC-11 expression system were in agreement with this findings: neither addition nor omission of SD sequence in the unstructured 5'-UTR affected the level of the reporter protein, non-specific nuclease NucB. Further, NucB level in P. bryantii TC1-1, contrary to hMGFP level in Eschericihia coli, was five times lower when SD sequence formed part of the secondary structure with a folding energy -5,2 kcal/mol. Also, the extended SDsequences did not affect protein levels as in E. coli. It seems therefore that a functional SD interaction does not take place during the translation initiation in P. bryantii TC1-1 and possibly other members of phylum Bacteroidetes although the anti SD sequence is present in 16S rnRNA genes of their genomes. We thus propose that in the absence of the SD sequence interaction, the selection of genuine start codons in Bacteroidetes is accomplished by binding of ribosomal protein S1 to unstructured 5'UTR as opposed to coding region which is inaccessible due to mRNA secondary structure. Additionally, we found that sequence logos of region preceding the start codons may be used as taxonomical markers. Depending on whether complete sequence logo or only part of it, such as information content and base proportion at specific positions, is used, bacterial genera or families and insome cases even bacterial phyla can be distinguised.
COBISS.SI-ID: 2912136
The role of bacteriocins in different environments has not been throughly explained, mainly because of the difficulties related to the detection of their production. Nisin, an antimicrobial peptide produced by Lactococus lactis has a long history of safe use in food products and has been studied from many aspects of genetics, biosynthesis, immunity, regulation, and mode of action. Still, some aspects concerning the dynamics of nisin gene expression remain unknown, especially in complex media like cheese. The main objective of the present study was to quantify in a cheese-like medium the expression of nisin genes in L. lactis M78, a well-characterized nisin A producer isolated from raw milk. The expression of all 11 genes involved in nisin biosynthesis was evaluated during cheese production by real time reverse transcription-PCR. Total RNA was extracted from cheeses using a direct extraction method without prior separation of microbial cells. The M78 strain grew well in experimental cheeses, producing detectable amounts of nisin after 4 h fermentation. The presence of nisin as an activator modified both the expression of nisin genes and the accumulation of active nisin. Four groups could be distinguised based on gene expression as a function of time: nisA, nisFEG, nisRK and nisBTCIP. Based on nisin-producing strain growth, nisin activity, founction of nisin genes, and their location, correlations were established that contribute to the explanation of regulation of nisin biosynthesis and immunity. This study is the first in which the evolution of bacteriocin gene transcripts has been quantified rigorously in a cheese-like medium.
COBISS.SI-ID: 2799240
The aim of this study was to compare recommendations for vitamin E supplementation regarding high polyunsaturated fatty acid intake and to compare the bioactivity of RRR- and allrac[alfa]-tocopherol with respect to oxidative stress in vivo and the oxidative stability of broiler meat. Fifty male broilers were divided into 5 groups. All groups received diets with a high inclusion of fat (7.5%), one with palm fat and the others with linseed oil, which were either unsupplemented of supplemented with vitamin E to contain in total 85 or 200 IU of vitamin E as all-rac-[alfa]-tocopherol and 85 IU as RRR-[alfa]tocopherol. Oxidative stress in vivo was studied by measuring the DNA damage; measuring malondialdehyde (MDA) in plasma, liver, and breast muscle; and analyzing the antioxidant capacity of the lipid-soluble compounds, total antioxidant status of plasma, and antioxidant enzyme assays. The tocopherols in plasma, liver, and breast muscle were also analyzed. In vitro oxidative stability was studied by measuring MDA in fresh, stored, and heat-treated brest meat. Linseed oil, opposed to palm fat, induced DNA fragmentation and MDA formation. Both forms and concentrations of vitamin E reduced DNA damage and breast muscle MDA. The groups receiving 200 IU of all-rac-[alfa]-tocopherol and 85 IU of RRR-[alfa]-tocopherol had much higher values for antioxidant capacity of lipid-soluble compounds than did the controls. No differences were observed in the values of antioxidant enzymes. The [alfa]-tocopherol levels in tissues and plasma were significantly influenced by the level of [alfa]-tocopherol supplementation. Malondialdehyde formation in meat from the vitamin E-supplemented groups was decreased in comparison with that from the control linseed oil group. We conclude that both vitamin E concentrations were insufficient to prevent all harmfull effects of lipid oxidation in vivo and that both were equally effective. On the contrary, to ensure good stability of meat lipids, higher vitamin E supplementation is needed, especially after heat treatment. The results of in vivo oxidative stress and meat lipid oxidation confirmed the currently accepted bioactivity of the RRR-[alfa]- to all-rasc=[alfa]-tocopherol ratio of 1.39 in in vivo and in vitro systems.
COBISS.SI-ID: 2888840