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71.
The mortars covering some walls of the Roman city of Baelo Claudia (Cadiz, Spain) support an abundant colonization of cyanobacteria, algae and lichens. The distribution of these organisms is closely related to microclimatic parameters. Furthermore, the development, specific composition and biomass of algal cryptoendolithic communities are related to the wall orientation. The effect of these communities on mortar deterioration is discussed. 相似文献
72.
V. Kumar J. L. de la Fuente A. L. Leitão P. Liras J. F. Martin 《Applied microbiology and biotechnology》1996,45(5):621-628
The bla gene of the cephamycin cluster of Nocardia lactamdurans has been subcloned in the shuttle plasmids pULVK2 and pULVK2A and amplified in N. lactamdurans LC411. The transformants showed two- to threefold higher β-lactamase activity. Formation of β-lactamase preceded the onset
of cephamycin biosynthesis. The β-lactamase of N. lactamdurans inactivated penicillins and, to a lesser extent, cephalosporin C but did not hydrolyse cephamycin C. This β-lactamase was
highly sensitive to clavulanic acid (50% inhibition was observed at 0.48 μg/ml clavulanic acid). The N. lactamdurans bla gene was disrupted in vivo by inertion of the kanamycin-resistance gene. Three bla-disrupted mutants, BD4, BD8 and BD12, were selected that lacked β-lactamase activity. Overexpresion of the bla gene resulted in N. lactamdurans transformants that were resistant to penicillin whereas mutants in which the bla gene was disrupted were supersensitive to this antibiotic. The three N. lactamdurans mutants with the bla gene disrupted showed a significant increase of cephamycin biosynthesis in solid medium, whereas transformants with the amplified
bla gene produced reduced levels of cephamycin. The cephamycin-overproducing Merck strain N. lactamdurans MA4213 showed no detectable levels of β-lactamase activity. The β-lactamase plays a negative role in cephamycin biosynthesis
in solid medium, but not in liquid medium.
Received: 26 July 1995/Received revision: 18 December 1995/Accepted: 8 January 1996 相似文献
73.
M El Mzibri C. Beudot M. De Méo M. Laget H. Guiraud G. Duménil 《Biotechnology letters》1996,18(8):933-936
Summary Two S. typhimurium strains TA1534 (rfa
+) and TA1538 (rfaE) were transformed with the lamB expression plasmid pAMH70. Transposition events with placMu55 hybrid phage were successful only with TA1534/pAMH70 strain. Using SDS-PAGE, the LamB protein was present in the total cell proteins but not in the outer membrane proteins of the TA1538/pAMH70 strain. The LamB protein must linked to the LPS of the outer membrane to allow adsorption of phage in S. typhimurium. 相似文献
74.
Figueiredo A. Cristina Almendra M. João Barroso José G. Scheffer Johannes J. C. 《Biotechnology letters》1996,18(8):863-868
The transformation capacity of Achillea millefolium L. ssp. millefolium (yarrow) cell suspension cultures was investigated using geraniol (50mg/l) and borneol, menthol, thymol and farnesols (25mg/l) as substrates. Apart from converting these substrates into several biotransformation products, the cell suspension cultures were also able to glycosylate both the substrates and the biotransformation products. aa]Key Words bb]Achillea millefolium L. ssp. millefolium bb]Yarrow bb]Compositae bb]Biotransformation bb]Glycosylation bb]Geraniol bb]Borneol bb]Menthol bb]Thymol bb]Farnesols 相似文献
75.
Marcello Franco Eduardo Bagagli Marino Cunha Luiz Gastão Chamma Denise Fecchio 《Mycopathologia》1996,135(1):13-19
We investigated the occurrence of antigenic and biochemical variability among Paracoccidioides brasiliensis antigen batches prepared according to the same protocol. Initially (experiment #1), we analyzed two antigen lots of two human isolates (Bt1 & Bt2), cultured in two media (PYG: bactopeptone, yeast extract, glucose; MMM: McVeigh & Morton medium) in SDS-PAGE and in two immunological tests (imunodiffusion-ID and footpad swelling test-FPT). Afterwards (experiment #2), we compared the antigenic profile of three antigen batches from three human isolates (Bt1, Bt2 & Bt3) by two-dimensional immunoelectrophoresis (2 D-IEP) against a reference system for P. brasiliensis antigens. In experiment #1, there were important intra- and inter-strain antigenic differences between batches of the fungal isolates cultured on both media. The block titration of the antigen batches for the immunological tests revealed correlation between protein concentration and biological activity in ID and no correlation in FPT. In experiment #2, the reference system for P. brasiliensis showed 26 antigen peaks. There were important differences between batches prepared from the same isolate and between batches from different isolates. Our data suggested the occurrence of instability in the synthesis of antigenic components by a same P. brasiliensis isolate, under controlled incubation conditions. 相似文献
76.
Transport of acetic acid in Zygosaccharomyces bailii: effects of ethanol and their implications on the resistance of the yeast to acidic environments. 下载免费PDF全文
Cells of Zygosaccharomyces bailii ISA 1307 grown in a medium with acetic acid, ethanol, or glycerol as the sole carbon and energy source transported acetic acid by a saturable transport system. This system accepted propionic and formic acids but not lactic, sorbic, and benzoic acids. When the carbon source was glucose or fructose, the cells displayed activity of a mediated transport system specific for acetic acid, apparently not being able to recognize other monocarboxylic acids. In both types of cells, ethanol inhibited the transport of labelled acetic acid. The inhibition was noncompetitive, and the dependence of the maximum transport rate on the ethanol concentration was found to be exponential. These results reinforced the belief that, under the referenced growth conditions, the acid entered the cells mainly through a transporter protein. The simple diffusion of the undissociated acid appeared to contribute, with a relatively low weight, to the overall acid uptake. It was concluded that in Z. bailii, ethanol plays a protective role against the possible negative effects of acetic acid by inhibiting its transport and accumulation. Thus, the intracellular concentration of the acid could be maintained at levels lower than those expected if the acid entered the cells only by simple diffusion. 相似文献
77.
On Normandy coasts, the red alga Delesseria sanguinea perennates by its stipe; fronds grow in January and disappear in June. Seasonal variations in sterol composition in relation to the biology of D. sanguinea are reported. Sterols in cellular membranes are free or conjugated by esterification with fatty acids, heterosides or lipid complexes like phospholipids. Both kinds of sterols were analyzed by GC-MS. The major sterol (80%) found in fronds was cholesterol whereas in stipes, cholesterol was also the major sterol in spring, but in September, an important reduction in cholesterol yield was noted with proportional increase in sitosterol content. It appears that cholesterol is synthesized in fronds in spring, then transferred to the stipe, which loses an important amount of cholesterol with loss of the blades. 相似文献
78.
Ammonium concentrations were determined in near-bottom water and intertidal surface sediments collected in February and July 1993 at five stations of Ria Formosa, a shallow meso-tidal coastal lagoon in southern Portugal. At each station, samples were taken a few minutes before tidal inundation, and subsequently 2, 10, 15 and 20 minutes thereafter. Ammonium concentration in near-bottom waters increased dramatically in the first 2 minutes followed by a decrease during the 18 minutes of flooding (maximum range 10.3-2.2 M). The highest levels in the flooding water were concomitant with a decrease of extractable ammonium recorded in the upper sediment layer (2 cm). Laboratory experiments indicated that ammonium is easily extracted from the sediment solids by physical perturbation, as one would expect when tidal water flushes over the intertidal area. This perturbation results in the export of ammonium from the sediment, by pulse mechanisms of short time intervals. On a daily scale this amount is two orders of magnitude higher than transport resulting from molecular diffusion. 相似文献
79.
Medium-chain fatty acids (C6 to C12), produced by yeast metabolism during alcoholic fermentation, are known to be inhibitory to lactic acid bacteria. The purpose of this work was to clarify the effect of both ethanol and decanoic and dodecanoic acids on the growth and malolactic activity of aLeuconostoc oenos strain isolated from Portuguese red wine. Ethanol in concentrations up to 12% had no significant effect on malolactic activity but strongly inhibited cell growth. The fatty acids decanoic acid, in concentrations up to 12.5 mg l–1, and, dodecanoic acid up to 2.5 mg l–1 seemed to act as growth factors stimulating also malolactic activity; at higher concentrations they exerted an inhibitory effect. We found clear pH dependence between pH 3.0 and pH 6.0, between decanoic acid concentration and its effect on malolactic activity, indicating that the undissociated molecule is the active form. At pH 3.0 the results can be explained by considering that fatty acids enter the cell as protonated molecules and dissociate in the cytoplasm due to the higher internal pH, leading to increased intracellular hydrogenous concentration. This may be the basis of two different effects that contribute to the observed inhibition: decrease in the intracellular pH and dissipation of the transmembrane proton gradient, thus inhibiting intracellular enzymes and ApH-dependent transport systems. 相似文献
80.