1,721,060 research outputs found
Carbon dioxide metabolism in Streptococcus thermophilus : physiological and ecological importance, and dairy applications
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Selfish and cooperative strategies, two energetic behaviors driven by environmental constraints
No full textNutrient richness, and specifically the abundance of mono- and disaccharides that characterize several food matrixes, such as milk and grape juice, has allowed the speciation of lactic acid bacteria and yeasts with a high fermentation capacity instead of energetically favorable respiratory metabolism. In these environmental contexts, rapid sugar consumption and lactic acid or ethanol production, accumulation and tolerance, together with the ability to propagate in the absence of oxygen, are several of the ‘winning’ traits that have apparently evolved and become specialized to perfection in these fermenting microorganisms. Here, we summarize and discuss the evolutionary context that has driven energetic metabolism in food-associated microorganisms, using the dairy species Lactococcus lactis and Streptococcus thermophilus among prokaryotes and the bakers’ yeast Saccharomyces cerevisiae among eukaryotes as model organisms
Phosphoenolpyruvate carboxylase activity is essential for the growth of Streptococcus thermophilus in milk
No full textVirome-associated antibiotic-resistance genes in an experimental aquaculture facility
Full text linkWe report the comprehensive characterization of viral and microbial communities within an aquaculture wastewater sample, by a shotgun sequencing and 16S rRNA gene profiling metagenomic approach. Caudovirales had the largest representation within the sample, with over 50% of the total taxonomic abundance, whereas approximately 30% of the total open reading frames (ORFs) identified were from eukaryotic viruses (Mimiviridae and Phycodnaviridae). Antibiotic resistance genes (ARGs) within the virome accounted for 0.85% of the total viral ORFs and showed a similar distribution both in virome and in microbiome. Among the ARGs, those encoding proteins involved in the modulation of antibiotic efflux pumps were the most abundant. Interestingly, the taxonomy of the bacterial ORFs identified in the viral metagenome did not reflect the microbial taxonomy as deduced by 16S rRNA gene profiling and shotgun metagenomic analysis. A limited number of ARGs appeared to be mobilized from bacteria to phages or vice versa, together with other bacterial genes encoding products involved in general metabolic functions, even in the absence of any antibiotic treatment within the aquaculture plant. Thus, these results confirm the presence of a complex phage-bacterial network in the aquaculture environment
Integrated approaches for the production of vanillin
No full textVanillin is the molecule responsible for the well-known vanilla aroma, and therefore one of the most used flavour components in the food and cosmetic industries. Vanillin is mostly produced via a chemical process, with only a small fraction extracted from natural sources, namely, the bean of the orchid Vanilla planifolia. The consumer demand for natural vanillin highly exceeds the amount of vanillin extracted by plant sources and new methods for the production of natural vanillin have been attempted. Biotransformation of natural substrates into vanillin is an alternative way to produce the natural flavour. Ferulic acid can be obtained by hydrolysis of the lignin fraction of plant biomasses and converted into vanillin using engineered microorganisms. Our work has been focused on solving the major challenges in obtaining preparative bioprocesses are: the availability of methods for hydrolysis and recovery of ferulic acid from biomasess, the construction of stable and productive engineered microorganisms with high tolerance towards the vanillin produced, the optimization of fermentation/biotransformation, and finally efficient protocols for vanillin recovery.
Examples from our work will be presented with regards to different strategies for identifying an integrated approach for biotechnological vanillin production
Single-growing units heterogeneity in Streptococcus thermophilus
No full textMicrobial cell individuality is a source of phenotypic heterogeneity. This heterogeneity is related to stochastic fluctuations in transcription or translation, despite genetically homogeneous background and constant environment conditions. Heterogeneity at a single-cell level is typically masked in conventional studies of microbial populations, which are based on the average behaviour of thousands or millions of cells. Here we developed a semi-automated protocol to study the growth kinetics parameters of single-growing unit (single cell or single-chain) in the dairy bacterium S. thermophilus. The results obtained revealed an unexpected heterogeneity in the lag-phase and max-velocity showing a modal distribution of the measured values. Lag-phase and max-velocity values have been significantly modified by changing the energetic status of the single-growing units before their transfer into a new medium. The approach developed could be useful to set-up the best environmental perturbations able to reduce or increase the phenotypic single-cell heterogeneity in S. thermophilus population
Bioluminescence-based identification of nisin producers - a rapid and simple screening method for nisinogenic bacteria in food samples
No full textWe present a simple and rapid method for screening nisin producers that directly identifies nisinogenic bacteria by induction of bioluminescence within the Lactococcus lactis NZ9800lux biosensor strain (Immonen and Karp, 2007, Biosensors and Bioelectronics 22, 1982-7). An overlay of putative nisinogenic colonies with the biosensor strain gives identification results within 1h. Functionality and specificity of the method were verified by screening nisin producers among 144 raw milk colonies and a panel of 91 lactococcal strains. Studies performed on strains and colonies that did not induce bioluminescence but inhibited growth of the biosensor demonstrated that only nisinogenic bacteria can cause induction. Bacteria known to produce bacteriocins other than nisin failed to induce bioluminescence, further verifying the specificity of the assay. We discovered a non-inducing but inhibitory lactococcal strain harboring a modified nisin Z gene, and demonstrated that the source of the inhibitory action is not a non-inducing variant of nisin, but a bacteriocin of lower molecular weight. The concentration of nisin producers in a raw milk sample was 1.3 × 10(2)CFU/ml. We identified from raw milk a total of seven nisin Z producing L. lactis subsp. lactis colonies, which were shown by genetic fingerprinting to belong to three different groups. Among the panel of 91 lactococci, four strains were nisin A producers, and one strain harbored the modified nisin Z gene. The method presented here is robust, cost-effective and simple to perform, and avoids the pitfalls of traditional screening methods by directly specifying the identity of the inhibitory substance
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