Sensitivity of capsular-producing Streptococcus thermophilus strains to bacteriophage adsorption

Aims: To determine whether the presence and type of exopolysaccharides (EPS), slime‐EPS or capsular, and the structural characteristics of the polymers produced by Streptococcus thermophilus strains could interfere with or be involved in phage adsorption. Methods and Results: Phage–host interactions between eight EPS‐producing Strep. thermophilus strains (CRL419, 638, 804, 810, 815, 817, 821, 1190) and five streptococcus specific phages (φYsca, φ3, φ5, φ6, φ8) isolated from Argentinean faulty fermentation failed yoghurts were evaluated. No relationship was found between the EPS chemical composition and the phage sensitivity/resistance phenotype. In general, the capsular‐producing strains were more sensitive to phage attacks than the noncapsular‐producing strains. Streptococcus thermophilus CRL1190 (capsular‐producing) was the only strain sensitive to all bacteriophages and showed the highest efficiency of plating. Phage adsorption to a capsular‐negative, EPS low‐producing mutant of strain CRL1190 was reduced, especially for φYcsa and φ8. Conclusions: The presence of capsular polysaccharide surrounding the cells of Strep. thermophilus strains could play a role in the adsorption of specific phages to the cells. Significance and Impact of the Study: Capsular‐producing Strep. thermophilus strains should be evaluated for their bacteriophage sensitivity if they are included in starter cultures for the fermented food industry.     

Isolation and Characterization of a Slowly Milk-Coagulating Variant of Lactobacillus helveticus Deficient in Purine Biosynthesis

A slowly milk-coagulating variant (Fmc⁻) of Lactobacillus helveticus CRL 1062, designated S1, was isolated and characterized. Strain S1 possessed all the known essential components required to utilize casein as a nitrogen source, which include functional proteinase and peptidase activities as well as functional amino acid, di- and tripeptide, and oligopeptide transport systems. The amino acid requirements of strain S1 were similar to those of the parental strain. However, on a purine-free, chemically defined medium, the growth rate of the Fmc⁻ strain was threefold lower than that of the wild-type strain. L. helveticus S1 was found to be defective in IMP dehydrogenase activity and therefore was deficient in the ability to synthesize XMP and GMP. This conclusion was further supported by the observation that the addition of guanine or xanthine to milk, a substrate poor in purine compounds, restored the Fmc⁺ phenotype of L. helveticus S1.     

Sequential transfer of left-right information during vertebrate embryo development

The establishment of left-right asymmetries in the vertebrate embryo is carried out by complex genetic interactions that impart left- or right-sided information to the developing organs and structures. The origin of LR information is still unclear, but recent advances have provided new insights as to how it is relayed to the embryo node, and thereafter to the lateral plate mesoderm. In both steps, signaling by members of the transforming growth factor-beta superfamily plays critical roles in amplifying and spreading LR cues, which are reviewed here.     

Selection of bacteriocin producer strains of lactic acid bacteria from a dairy environment

Two strains showing bacteriocin production were selected from a total of 206 lactic acid bacteria isolated from samples of milk, milk serum, whey and homemade cheeses in Southern Cordoba, Argentina. This property was detected by means of well diffusion assays. The strains were identified as Enterococcus hirae and Enterococcus durans. The protein nature of those substances was proved by showing their sensitivity to type IV and XXV proteases, papaine, trypsin, pepsin and K proteinase. The bacteriocins inhibited the growth of Listeria monocytogenes, Bacillus cereus, Clostridium perfringes and two strains of Staphylococcus aureus, an A-enterotoxin and a B-enterotoxin producers. All of these bacteria are common pathogens usually associated with food borne diseases (ETA). These lactic acid bacteria or their bacteriocins could be suitable candidates for food preservation and specially useful in the our regional dairy industry.     

NAD(P)H oxidase 1, a product of differentiated colon epithelial cells,can partially replace glycoprotein 91phox in the regulated production of superoxide by phagocytes

Reactive oxygen species (ROS) serve several physiological functions; in some settings they act in host defense, while in others they function in cellular signaling or in biosynthetic reactions. We studied the expression and function of a recently described source of ROS, NAD(P)H oxidase 1 or Nox1, which has been associated with cell proliferation. In situ hybridization in mouse colon revealed high Nox1 expression within the lower two-thirds of colon crypts, where epithelial cells undergo proliferation and differentiation. Human multitumor tissue array analysis confirmed colon-specific Nox1 expression, predominantly in differentiated epithelial tumors. Differentiation of Caco2 and HT29 cells with 1alpha,25-dihydroxyvitamin D(3) or IFN-gamma enhances Nox1 expression and decreases cell proliferation, suggesting that Nox1 does not function as a mitogenic oxidase in colon epithelial cells. Transduction with retrovirus encoding Nox1 restored activation and differentiation-dependent superoxide production in gp91(phox)-deficient PLB-985 cells, indicating close functional similarities to the phagocyte oxidase (phox). Furthermore, coexpression of cytosolic components, p47(phox) and p67(phox), augments Nox1 activity in reconstituted K562 cells. Finally, Nox1 partially restores superoxide production in neutrophils differentiating ex vivo from gp91(phox)-deficient CD34(+) peripheral blood-derived stem cells derived from patients with X-linked chronic granulomatous disease. These studies demonstrate a significant functional homology (cofactor-dependent and activation-regulated superoxide production) between Nox1 and its closest homologue, gp91(phox), suggesting that targeted up-regulation of Nox1 expression in phagocytic cells could provide a novel approach in the molecular treatment of chronic granulomatous disease.     

MKP3 mediates the cellular response to FGF8 signalling in the vertebrate limb

The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and phosphatidylinositol-3-OH kinase (PI3K)/Akt pathways are involved in the regulatory mechanisms of several cellular processes including proliferation, differentiation and apoptosis. Here we show that during chick, mouse and zebrafish limb/fin development, a known MAPK/ERK regulator, Mkp3, is induced in the mesenchyme by fibroblast growth factor 8 (FGF8) signalling, through the PI3K/Akt pathway. This correlates with a high level of phosphorylated ERK in the apical ectodermal ridge (AER), where Mkp3 expression is excluded. Conversely, phosphorylated Akt is detected only in the mesenchyme. Constitutively active Mek1, as well as the downregulation of Mkp3 by small interfering RNA (siRNA), induced apoptosis in the mesenchyme. This suggests that MKP3 has a key role in mediating the proliferative, anti-apoptotic signalling of AER-derived FGF8.     

Deoxyribonuclease activities in Lactobacillus delbrueckii

DNase activity was examined in the extracellular and subcellular fractions of six non-transformable strains belonging to Lactobacillus delbrueckii subsp. lactis (L. lactis) and Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) and compared with the activity present in Lactobacillus johnsonii NCK 65, a transformable strain of Lactobacillus. In the extracellular fraction of the L. delbrueckii strains, a common protein band of 36 kDa was detected, while a band of 29 kDa was found in the same fraction of L. johnsonii. No nuclease activity was detected in the cytoplasmic fraction of this strain, indicating that the localization of the DNase activity could be a key factor in the uptake of foreign DNA.     

Nest desertion cannot be considered an egg‐rejection mechanism in a medium‐sized host: an experimental study with the common blackbird Turdus merula

Two main mechanisms of egg rejection, the main defence of hosts against brood parasites, have been described: ejection and desertion. Desertion of the parasitized nest is much more costly and is usually exhibited by small‐sized host species unable to remove the parasitic egg. However, nest desertion is frequently assumed to be an anti‐parasite strategy even in medium or large‐sized host species. This assumption should be considered with caution because: 1) large‐sized hosts able to eject the parasitic egg should eject it rather than desert the nest, and 2) breeding birds may desert their nests in response to different disturbances other than brood parasitism. This problem is especially important in the common blackbird Turdus merula because this is a medium‐sized species, potential host of the common cuckoo Cuculus canorus, in which desertion has been frequently reported as a response to cuckoo egg models. Here, we seek to determine whether nest desertion can be considered a response unequivocally directed to the parasitic egg in medium‐sized hosts using the blackbird as the study species. In an experimental study in which we have manipulated levels of mimicry and size of experimental eggs, we have found that both colour (mimetic and non‐mimetic; at least for human vision) and size (small, medium, and large) significantly affected ejection rates but not nest desertion rates. In fact, although large eggs disproportionally provoked nest desertion more frequently than did small or medium‐sized eggs, cuckoo‐sized parasitic eggs were not deserted allowing us to conclude that desertion is unlikely to be an adaptive response to brood parasitism at least for this species.     

Use of SDS-PAGE of cell-wall proteins for rapid differentiation of Lactobacillus delbrueckii subsp. lactis and Lactobacillus helveticus

Cell-wall protein profiles of different strains of Lactobacillus helveticus and L. delbrueckii subsp. lactis isolated from regional cheeses were studied by SDS-PAGE. The patterns were highly reproducible and the presence of numerous bands with molecular weight ranging from 14 to 160 kDa allowed L. delbrueckii subsp. lactis to be differentiated from L. helveticus. The method is a reliable and rapid way to identify thermophilic lactobacilli.