Growth medium

About: Growth medium is a research topic. Over the lifetime, 1889 publications have been published within this topic receiving 59171 citations. The topic is also known as: culture medium & culture media.

The freezing points of bacterial cells in relation to halophilism.

Abstract: SUMMARY: The hypothesis that halophilic bacteria achieve a high degree of salt tolerance by exclusion of much of the external solutes of the growth medium has been tested. Organisms were grown in media containing from 1 to 4 m salts. For both halophilic and non-halophilic bacteria the freezing points of the cells were close to those of the media in which they were grown. It is concluded that halophilic bacteria do not maintain the intracellular aqueous phase at a water activity greater than in the surrounding growth medium.

In vitro uptake of minerals by Gypsophila paniculata and hybrid eucalypts, and relevance to media mineral formulation

Abstract: Despite the importance of mineral nutrition for plantlet growth in vitro, there have been few studies on mineral uptake from growth media or on optimising the media used in tissue culture. As plants in vitro experience abnormal growth conditions and may not possess roots, they may use different mechanisms of mineral uptake than plants growing ex vitro. To examine this possibility, plantlets of Gypsophila paniculata were grown on media in which the K or Ca concentration was varied. Mineral analysis showed a linear relationship between concentrations of K or Ca in the growth medium and plantlet tissues, suggesting uptake is by passive diffusion. However, interactions occurred between K, Ca and Mg uptake; therefore, other mechanisms are also likely to be involved in regulating mineral concentrations in tissue. The study also demonstrated that critical mineral concentrations could be estimated by using tissue-culture systems, as the concentration ranges of K and Ca in vitro correlated well with data for a related species ex vitro. This knowledge of critical concentrations, in conjunction with tissue analysis and ion speciation modelling, can be used to optimise in vitro mineral formulations through cycles of culture, tissue analysis and medium reformulation. To test this proposal, plantlets of Eucalyptus europhylla × grandis were grown on a proprietary medium formulation (SEM) and one modified as a result of tissue analysis (MEM). Plantlets cultured on SEM had chlorotic leaves and serious mineral imbalances. In contrast, plantlets cultured on MEM were not chlorotic, had more uniform growth and a more balanced mineral content. However, modification of mineral concentrations in the culture medium did not always result in similar changes in plant tissues. These differences in the proportions of minerals in the medium and those in the plant indicate that there are interactions between minerals in the medium and/or between minerals and the agar matrix that influence mineral availability and uptake.

Function and transcriptional regulation of the isocitrate lyase in Pseudomonas aeruginosa.

Abstract: Pseudomonas aeruginosa ATCC 17933 is capable of growing aerobically on ethanol as sole source of carbon and energy. This requires the glyoxylate cycle for replenishing C4-compounds to the TCA cycle. The enzyme isocitrate lyase (ICL) catalyzes the first step of this glyoxylate shunt. Its activity was induced more than 10-fold in response to the carbon sources ethanol or acetate instead of glucose or succinate. We could prove that in P. aeruginosa ICL is essential for aerobic as well as anaerobic utilization of C2-sources. Transcriptional regulation of icl gene (aceA) expression was monitored on different carbon sources by using an aceA-lacZ gene fusion. A strong correlation between promoter and ICL activity indicated regulation at the transcriptional level. But ICL was not simply induced by the mere presence of ethanol in the growth medium as was demonstrated by cultivation on mixed substrates. P. aeruginosa showed diauxic growth on media containing ethanol-succinate or ethanol-glucose mixtures and did not transcribe the aceA gene to metabolize ethanol until succinate or glucose, respectively, were exhausted. Inactivation of the chromosomal aceA gene in P. aeruginosa led to an inability to grow on ethanol and acetate. Promoter activity studies showed that all genes necessary to oxidize ethanol were downregulated in the ICL-negative mutant. But on mixed substrates like ethanol-succinate or ethanol-glucose the mutant exhibited growth and utilized ethanol as well, probably as energy source only.