Natürliche Konservierung fürs Joghurt

Dieser Artikel wurde mit freundlicher Genehmigung des Verlags zweitveröffentlicht

Natürliche Konservierung fürs Joghurt

Dieser Artikel wurde mit freundlicher Genehmigung des Verlags zweitveröffentlicht

A novel multiplex PCR/RFLP assay for the identification of Streptococcus bovis/Streptococcus equinus complex members from dairy microbial communities based on the 16S rRNA gene

The Streptococcus bovis/Streptococcus equinus complex (SBSEC) comprises pathogenic species associated with different degrees with human infections but also spontaneously fermented dairy products. We aimed therefore at developing a specific identification assay for the SBSEC targeting the 16S rRNA gene comprising a multiplex PCR followed by a differentiating restriction fragment length polymorphisms (RFLP). The multiplex PCR assay was positively applied on 200 SBSEC isolates including reference strains. The assay did not yield false-positive amplifications with strains of closely related bacteria and isolates of non-SBSEC streptococci, lactococci, enterococci, and other genera of dairy origin. The downstream RFLP using MseI and XbaI enabled further discrimination of Streptococcus infantarius/S. bovis (biotype II.1) from Streptococcus gallolyticus (biotype I and II.2)/Streptococcus alactolyticus and S. equinus. Furthermore, the newly developed primers can be used directly for Sanger sequencing. Conclusively, this novel PCR/RFLP assay is applicable in the complex dairy microbial communities and provides an important tool to assess the prevalence of members of the SBSEC in dairy product

Recent developments in cheese cultures with protective and probiotic functionalities

Microorganisms play essential roles in the manufacture and ripening of cheese, largely contributing to the development of organoleptic properties by their metabolism and varied enzymatic activities, and to microbiological safety through barrier effects of complex microflora and production of several low-molecular-weight antimicrobial compounds. Although extensive research has been done on bacteriocins of cheese bacteria for controlling pathogens in cheese, until now only few applications have emerged. The control of spoilage yeasts and moulds has been traditionally done by chemical additives, but the application of new antifungal protective cultures is very promising, especially for the cheese industry. It has also been recently shown that naturally established cheese microflora can efficiently prevent the growth of pathogenic or spoilage microorganisms. Cheese is also a very suitable but underused carrier for the delivery of probiotic bacteria, conferring health benefits on the host, with specific advantages compared with fermented milks and yoghurts such as high cell viability. This review addresses the latest developments in applications of protective cultures (with bacteriocin and antifungal activities) or microflora with barrier effects, and probiotic cultures for the production of high quality, safe and "healthy” cheese, as well as emphasizing some of the underlying challenges and possible solutions. Furthermore, new safety criteria for food cultures relating to the presence and transferability of antibiotic resistance genes are discusse

The Effect of Saturated Fatty Acids on Methanogenesis and Cell Viability of Methanobrevibacter ruminantium

Saturated fatty acids (SFAs) are known to suppress ruminal methanogenesis, but the underlying mechanisms are not well known. In the present study, inhibition of methane formation, cell membrane permeability (potassium efflux), and survival rate (LIVE/DEAD staining) of pure ruminal Methanobrevibacter ruminantium (DSM 1093) cell suspensions were tested for a number of SFAs. Methane production rate was not influenced by low concentrations of lauric (C12; 1 μg/mL), myristic (C14; 1 and 5 μg/mL), or palmitic (C16; 3 and 5 μg/mL) acids, while higher concentrations were inhibitory. C12 and C14 were most inhibitory. Stearic acid (C18), tested at 10–80 μg/mL and ineffective at 37°C, decreased methane production rate by half or more at 50°C and ≥50 μg/mL. Potassium efflux was triggered by SFAs (C12 = C14 > C16 > C18 = control), corroborating data on methane inhibition. Moreover, the exposure to C12 and C14 decreased cell viability to close to zero, while 40% of control cells remained alive after 24 h. Generally, tested SFAs inhibited methanogenesis, increased cell membrane permeability, and decreased survival of M. ruminantium in a dose- and time-dependent way. These results give new insights into how the methane suppressing effect of SFAs could be mediated in methanogens

1,3-Propanediol dehydrogenases in Lactobacillus reuteri: impact on central metabolism and 3-hydroxypropionaldehyde production

<p>Abstract</p> <p>Background</p> <p><it>Lactobacillus reuteri </it>metabolizes glycerol to 3-hydroxypropionaldehyde (3-HPA) and further to 1,3-propanediol (1,3-PDO), the latter step catalysed by a propanediol dehydrogenase (PDH). The last step in this pathway regenerates NAD⁺and enables therefore the energetically more favourable production of acetate over ethanol during growth on glucose.</p> <p>Results</p> <p>A search throughout the genome of <it>L. reuteri </it>DSM 20016 revealed two putative PDHs encoded by ORFs lr_0030 and lr_1734. ORF lr_1734 is situated in the <it>pdu </it>operon encoding the glycerol conversion machinery and therefore likely involved in 1,3-PDO formation. ORF lr_0030 has not been associated with PDH-activity so far. To elucidate the role of these two PDHs, gene deletion mutant strains were constructed. Growth behaviour on glucose was comparable between the wild type and both mutant strains. However, on glucose + glycerol, the exponential growth rate of Δlr_0030 was lower compared to the wild type and the lr_1734 mutant. Furthermore, glycerol addition resulted in decreased ethanol production in the wild type and Δlr_1734, but not in Δlr_0030. PDH activity measurements using 3-HPA as a substrate revealed lower activity of Δlr_0030 extracts from exponential growing cells compared to wild type and Δlr_1734 extracts.</p> <p>During biotechnological 3-HPA production using non-growing cells, the ratio 3-HPA to 1,3-PDO was approximately 7 in the wild type and Δlr_0030, whereas this ratio was 12.5 in the mutant Δlr_1734.</p> <p>Conclusion</p> <p>The enzyme encoded by lr_0030 plays a pivotal role in 3-HPA conversion in exponential growing <it>L. reuteri </it>cells. The enzyme encoded by lr_1734 is active during 3-HPA production by non-growing cells and this enzyme is a useful target to enhance 3-HPA production and minimize formation of the by-product 1,3-PDO.</p

Rumen simulation technique study on the interactions of dietary lauric and myristic acid supplementation in suppressing ruminal methanogenesis

The interactions of lauric (C12) and myristic acid (C14) in suppressing ruminal methanogenesis and methanogens were investigated with the rumen simulation technique (Rusitec) using bovine ruminal fluid. The fatty acids were added to basal substrates (grass hay:concentrate, 1:1.5) at a level of 48 g/kg DM, provided in C12:C14 ratios of 5:0, 4:1, 3:2, 2·5:2.5, 2:3, 1:4 and 0:5. Additionally, an unsupplemented control consisting of the basal substrates only was employed. Incubation periods lasted for 15 (n 4) and 25 (n 2) d. CH4 formation was depressed by any fatty acid mixture containing at least 40 % C12, and effects persisted over the complete incubation periods. The greatest depression (70 % relative to control) occurred with a C12:C14 ratio of 4:1, whereas the second most effective treatment in suppressing CH4 production (60 % relative to control) was found with a ratio of 3:2. Total methanogenic counts were decreased by those mixtures of C12 and C14 also successful in suppressing methanogenesis, the 4:1 treatment being most efficient (60 % decline). With this treatment in particular, the composition of the methanogenic population was altered in such a way that the proportion of Methanococcales increased and Methanobacteriales decreased. Initially, CH4 suppression was associated with a decreased fibre degradation, which, however, was reversed after 10 d of incubation. The present study demonstrated a clear synergistic effect of mixtures of C12 and C14 in suppressing methanogenesis, mediated probably by direct inhibitory effects of the fatty acids on the methanogen

Tn6198, a novel transposon containing the trimethoprim resistance gene dfrG embedded into a Tn916 element in Listeria monocytogenes

Objectives To characterize Tn6198, a novel conjugative transposon from the clinical Listeria monocytogenes strain TTH-2007, which contains the tetracycline and trimethoprim resistance genes tet(M) and dfrG, respectively, and to assess its transferability in vitro and in situ. Methods The complete sequence of Tn6198 was determined using a primer walking strategy. Horizontal gene transfer studies were performed by filter matings, as well as on the surface of smear-ripened cheese and smoked salmon. The presence of Tn916-like circular intermediates was determined by PCR. Antibiotic resistance was determined by the broth microdilution method and microarray hybridization. Results Sequencing of Tn6198 revealed that a 3.3 kb fragment containing dfrG was integrated between open reading frames 23 and 24 of Tn916. Furthermore, an additional copy of Tn916 was present in L. monocytogenes TTH-2007. Both elements were transferred simultaneously and separately in vitro to recipients L. monocytogenes 10403S and Enterococcus faecalis JH2-2 by conjugation, resulting in either tetracycline- and trimethoprim-resistant or solely tetracycline-resistant transconjugants. On the surface of cheese and salmon, only L. monocytogenes 10403S transconjugants were detected. Conclusions This study reports the first Tn916-like element associated with a trimethoprim resistance gene, as well as the first fully characterized transposon conferring multidrug resistance in L. monocytogenes. This is of concern, as trimethoprim is administered to listeriosis patients with β-lactam allergy and as Tn6198 has a large potential for dissemination, indicated by both intra-species and inter-genus transfe

Role of bacterial isolates in enhancing the bud induction in the industrially important red alga Gracilaria dura

Plant growth depends on the integration of environmental cues, nitrogen fixation and phytohormone-signaling pathways. The growth and development of Gracilaria dura was significantly influenced by the association of bacterial isolates. The putative bud-inducing epiphytic Exiguobacterium homiense and endophytic Bacillus pumilus, Bacillus licheniformis were examined for their ability to fix nitrogen and produce indole-3-acetic acid (IAA). These bacterial isolates were identified to the species level by biochemical tests, fatty acid and partial 16S rRNA gene sequence analysis. The B. pumilus, B. licheniformis and E. homiense produced 445.5, 335 and 184.1 μg mL−1 IAA and 12.51, 10.14 and 6.9 mM mL−1 ammonium, respectively, as determined using HPLC and spectroscopy. New bud regeneration observed after the addition of total protein of the bacterial isolates suggests that IAA is conjugated with protein. The epi- and endophytic bacterial isolates were able to induce five and 10 new buds per frond, respectively, in comparison to the control, where one to two buds were observed. The combination of 25 °C and 30‰ showed the optimum condition for bud induction in G. dura when incubated with the total protein of B. pumilus. Our finding revealed for the first time that IAA coupled with nitrogen fixation induce and regenerate new buds in G. dur

Construction and characterization of Enterococcus faecalis CG110/gfp/pRE25*, a tool for monitoring horizontal gene transfer in complex microbial ecosystems

Enterococci are among the most notorious bacteria involved in the spread of antibiotic resistance (ABR) determinants via horizontal gene transfer, a process that leads to increased prevalence of antibiotic-resistant bacteria. In complex microbial communities with a high background of ABR genes, detection of gene transfer is possible only when the ABR determinant is marked. Therefore, the conjugative multiresistance plasmid pRE25, originating from a sausage-associated Enterococcus faecalis, was tagged with a 34-bp random sequence marker spliced by tet(M). The plasmid constructed, designated pRE25*, was introduced into E. faecalis CG110/gfp, a strain containing a gfp gene as chromosomal marker. The plasmid pRE25* is fully functional compared with its parental pRE25, occurs at one to two copies per chromosome, and can be transferred to Listeria monocytogenes and Listeria innocua at frequencies of 6 × 10−6 to 8 × 10−8 transconjugants per donor. The markers on the chromosome and the plasmid enable independent quantification of donor and plasmid, even if ABR genes occur at high numbers in the background ecosystem. Both markers were stable for at least 200 generations, permitting application of the strain in long-running experiments. Enterococcus faecalis CG110/gfp/pRE25* is a potent tool for the investigation of horizontal ABR gene transfer in complex environments such as food matrices, biofilms or colonic model