Microbial sensor for penicillins using a recombinant strain of Escherichia coli.

E. coli harboring the multicopy plasmid pBR327, which codes for beta-lactamase synthesis, was immobilized on acetylcellulose membranes. These were placed in the vicinity of a flat pH electrode, thus constituting a penicillin biosensor based on the detection of changes in pH using a reference pH electrode. A response time of 8 min was obtained with at least 2 mg of cells cm-2 of membrane. A linear detection range between 5 and 30 mM of penicillin was achieved. Buffering capacity decreased the sensitivity, but to a lower extent as when compared with probes using purified enzyme. The sensor was completely stable for at least 13 days and proved to be useful for penicillin estimation in complex media such as fermentation broths and milk.     

Surface resistance to SSVs and SIRVs in pilin deletions of Sulfolobus islandicus

Characterizing the molecular interactions of viruses in natural microbial populations offers insights into virus–host dynamics in complex ecosystems. We identify the resistance of Sulfolobus islandicus to Sulfolobus spindle-shaped virus (SSV9) conferred by chromosomal deletions of pilin genes, pilA1 and pilA2 that are individually able to complement resistance. Mutants with deletions of both pilA1 and pilA2 or the prepilin peptidase, PibD, show the reduction in the number of pilins observed in TEM and reduced surface adherence but still adsorb SSV9. The proteinaceous outer S-layer proteins, SlaA and SlaB, are not required for adsorption nor infection demonstrating that the S-layer is not the primary receptor for SSV9 surface binding. Strains lacking both pilins are resistant to a broad panel of SSVs as well as a panel of unrelated S. islandicus rod-shaped viruses (SIRVs). Unlike SSV9, we show that pilA1 or pilA2 is required for SIRV8 adsorption. In sequenced Sulfolobus strains from around the globe, one copy of each pilA1 and pilA2 is maintained and show codon-level diversification, demonstrating their importance in nature. By characterizing the molecular interactions at the initiation of infection between S. islandicus and two different types of viruses we hope to increase the understanding of virus–host interactions in the archaeal domain.     

Biochemical and biophysical characterization of photosystem I from phytoene desaturase and zeta-carotene desaturase deletion mutants of Synechocystis Sp. PCC 6803: evidence for PsaA- and PsaB-side electron transport in cyanobacteria

In photosystem I, oxidation of reduced acceptor A(1)(-) through iron-sulfur cluster F(X) is biphasic with half-times of approximately 5-30 ns ("fast" phase) and approximately 150-300 ns ("slow" phase). Whether these biphasic kinetics reflect unidirectional electron transfer, involving only the PsaA-side phylloquinone or bi-directional electron transfer, involving both the PsaA- and PsaB-side phylloquinones, has been the source of some controversy. Brettel (Brettel, K. (1988) FEBS Lett. 239, 93-98) and Joliot and Joliot (Joliot, P., and Joliot, A. (1999) Biochemistry 38, 11130-11136) have attributed to nearby carotenoids electrochromic band shifts, accompanying A(1) reduction, centered at approximately 450 and 500-510 nm. As a test of these assignments, we separately deleted in Synechocystis sp. PCC 6803 the genes that encode phytoene desaturase (encoded by crtP (pds)) and zeta-carotene desaturase (encoded by crtQ (zds)). The pds(-) and zds(-) strains synthesize phytoene and zeta-carotene, respectively, both of which absorb to shorter wavelength than beta-carotene. Compared with wild type, the mutant A(1)(-) (FeS) - A(1)(FeS)(-) difference spectra, measured in cells and photosystem I complexes, retain the electrochromic band shift centered at 450 nm but show a complete loss of the electrochromic band shifts centered at 500-510 nm. Thus, the latter clearly arise from beta-carotene. In the wild type, the electrochromic band shift of the slow phase (centered at 500 nm) is shifted by 6 nm to the blue compared with the fast phase (centered at 506 nm). Thus, the carotenoid pigments acting as electrochromic markers during the fast and slow phases of A(1)(-) oxidation are different, indicating the involvement of both the PsaA- and the PsaB-side phylloquinones in photosystem I electron transport.     

Hypofractionation with concomitant boost using intensity-modulated radiation therapy in early-stage breast cancer in Mexico

Aim

To evaluate whether hypofractionation with integrated boost to the tumour bed using intensity-modulated radiation therapy is an acceptable option and to determine whether this treatment compromises local control, toxicity and cosmesis.

Microfiltration of streptococcal fermentation broths: study of the factors affecting the concentration effect

Streptokinase (SK) recovery from streptococcal fermentation broth by cross-flow microfiltration has been studied. Recovery of SK in the filtrate, independent of the volumetric concentration factor, is approximately two-fold lower than the initial SK activity in the fermentation broth; moreover, the SK activity in the retentate increase during the process, reaching a concentration factor of 2.73. These results show that the membrane works more as an ultrafiltration membrane, with rejection of S = 0.6, than as a microfiltration membrane. Under filtration conditions, the membrane permeation rate decreased with time. This decreased could be explained by deposition and interaction of material onto/with the membrane resulting in the concentration of permeable products. Studies of the individual concentration factors for the main streptococcal exocellular proteins, indicate clearly that the concentration of the proteins during the microfiltration process is independent of the size of the proteins, suggesting that other factors, such as charge and hydrophobicity, along with concentration-polarization, should be taken also into account for the understanding of this phenomenon. (c) 1994 John Wiley & Sons, Inc.     

Four eudesmanolides from Montanoa frutescens

Chemical analysis of Montanoa frutescens afforded the known sesquiterpene lactones montafrusins A and B, as well as four new eudesmanolides which we have named montafrusins C, D, E and F. The structures of the new compounds were established by spectroscopic methods.     

Bcl-2 protein in normal, hyperplastic and neoplastic breast tissues. A metabolite of the putative stem-cell subpopulation of the mammary gland

This investigation, though initially designed to examine the possible influence of the Bcl-2 protein on the node-metastasizing capacity of breast carcinomas, was amplified to study the expression of this anti-apoptotic protein in normal breast lobules and hyperplastic lesions. We examined paraffin sections of 508 breast carcinomas, stained for Bcl-2, estrogen (ER) and progesterone receptors (PgR) and epithelial membrane antigen, and occasionally for other antigens as well. Only a few cells showing a strong Bcl-2 positivity spotted the tubulo-lobular units of normal resting glands, whereas such cells were relatively numerous in atrophic lobules, and very scarce in the terminally differentiated lactating breast. Columnar and usual types of hyperplasia were exclusively, or almost exclusively, composed of Bcl-2(+), ER(+) and PgR(+) cells. The foci of carcinoma in situ and those of invasive carcinomas were respectively 83% and 66% positive for Bcl-2 in at least 25% of their cells. Even among the invasive carcinomas, Bcl-2(+) cases included 83% and 87% of the ER(+) and PgR(+) cases, respectively (p=0.0001). Though there was a statistically significant inverse relation between Bcl-2 and tumor grade (p=0.0001), no significant association was found between Bcl-2 and lymph node stage. In conclusion, we suggest that normal, hyperplastic and neoplastic breast epithelial cells expressing the anti-apoptotic protein Bcl-2 are immature cells that ought to form part of the stem-cell subpopulation, which is committed to the development and to the maintenance of the normal gland and which gives rise to hyperplastic and neoplastic disorders when its proliferation is deregulated. In ductal proliferative changes Bcl-2 assays may be useful for diagnostic but not for prognostic purposes.