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1.
In a continuing study of microbial secondary metabolism in
simulated microgravity, we have examined gramicidin S (GS) production by
Bacillus brevis strain Nagano in NASA High Aspect Rotating Vessels
(HARVs), which are designed to simulate some aspects of microgravity. Growth
and GS production were found to occur under simulated microgravity. When
performance under simulated microgravity was compared with that under normal
gravity conditions in the bioreactors, GS production was found to be
unaffected by simulated microgravity. The repressive effect of glycerol in
flask fermentations was not observed in the HARV. Thus the negative effect of
glycerol on specific GS formation is dependent on shear and/or vessel
geometry, not gravity.
Received: 7 August 1996 / Accepted: 17 September 1996 相似文献
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Keith W.T.Goulding 《中国科学:生命科学英文版》2005,48(Z2)
The nitrogen (N) cycle is essentially 'leaky'. The losses of small amounts of nitrate to waters and of ammonia and nitrous oxide to the atmosphere are a part of the global biogeo-chemical N cycle. However, intensive agricultural production, industry and vehicle use have more than doubled the amount of 'reactive' N in the environment, resulting in eutrophication, ecosystem change and health concerns. Research has identified agricultural practices that cause large losses of N and, in some cases, developed solutions. This paper discusses the problems of maintaining productivity while reducing N losses, compares conventional with low input (integrated) and organic farming systems, and discusses wider options. It also looks at the need to integrate studies on N with other environmental impacts, set in the context of the whole farm system, to provide truly sustainable agricultural systems. 相似文献
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A L Demain 《Biochemical and biophysical research communications》1966,24(1):39-43
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Juan F. Martin Arnold L. Demain 《Biochemical and biophysical research communications》1976,69(4):1103-1109
Phosphate concentration was found to control the biosynthesis of the antibiotic candicidin by resting cells of Streptomyces griseus. Phosphate concentrations above 1 mM decreased the rate of incorporation of [14C]propionate and [14C]p-aminobenzoic acid into candicidin in relation to the concentration of phosphate. The inhibitory effect of phosphate on incorporation of labeled precursors into candicidin was not caused by inhibition of cellular uptake of precursors. Protein synthesis, sensitive to chloramphenicol, was not affected by phosphate levels that inhibit antibiotic synthesis. Similarly, phosphate concentrations inhibitory to antibiotic synthesis did not affect rifampinsensitive RNA synthesis. 相似文献
10.
Addition of cyclic-AMP (c-AMP) to Streptomyces griseus fermentations inhibited candicidin formation. In a phosphate-free resting cell system, c-AMP inhibited net candicidin formation and incorporation of labeled propionate and p-aminobenzoic acid into the antibiotic but did not inhibit protein synthesis. All nucleotides tested, regardless of the position of the phosphate ester, were effective inhibitors; nucleosides and free bases were not. Inhibition occurred whether the nucleotide was added early or late. The results indicate that inhibition of antibiotic formation by exogenous nucleotides, including cyclic nucleotides, is similar to the effect produced by inorganic phosphate. 相似文献