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.

Aggregation in Azospirillum brasilense Cd: conditions and factors involved in cell-to-cell adhesion

Abstract: Aggregation of the root-inhabiting, asymbiotic N-fixingAzospirillum brasilense Cd (ATCC-29729), was studied Aggregation occurred towards the end of the exponential phase and during the stationary phase More aggregates were formed in media supplemented with organic acids than in those containing sugars as a sole carbon source Maximum growth with no aggregation was obtained in a medium containing both fructose and malate as carbon sources Aggregation was increased by poly-L-lysine and carbodiimide as well as by increasing the C/N ratio and decreasing combined nitrogen in the growth medium Aggregates were stable at pH levels of >8 and <6, but dispersed at pH 71 Treatment of Azospirillum with NaEDTA resulted in loss of both aggregative capacity and the ability of adsorb to wheat roots without losing cell viability When extracted bacteria were suspended in their dialysed NaEDTA extract, both their aggregative and adsorptive capacities were restored

High yield recombinant penicillin G amidase production and export into the growth medium using Bacillus megaterium.

Abstract: During the last years B. megaterium was continuously developed as production host for the secretion of proteins into the growth medium. Here, recombinant production and export of B. megaterium ATCC14945 penicillin G amidase (PGA) which is used in the reverse synthesis of β-lactam antibiotics were systematically improved. For this purpose, the PGA leader peptide was replaced by the B. megaterium LipA counterpart. A production strain deficient in the extracellular protease NprM and in xylose utilization to prevent gene inducer deprivation was constructed and employed. A buffered mineral medium containing calcium ions and defined amino acid supplements for optimal PGA production was developed in microscale cultivations and scaled up to a 2 Liter bioreactor. Productivities of up to 40 mg PGA per L growth medium were reached. The combination of genetic and medium optimization led to an overall 7-fold improvement of PGA production and export in B. megaterium. The exclusion of certain amino acids from the minimal medium led for the first time to higher volumetric PGA activities than obtained for complex medium cultivations.

Regulated expression of the nor-1 and ver-1 genes associated with aflatoxin biosynthesis.

Abstract: RNA transcript accumulation for the ver-1 and nor-1 genes, which are associated with aflatoxin biosynthesis in the fungus Aspergillus parasiticus, was measured before and during aflatoxin production in liquid shake culture. Transcripts were not detected until near the end of trophophase (growth phase) and could still be observed well into stationary phase during batch fermentation in an aflatoxin-supporting growth medium. Maximum accumulation of both transcripts occurred just prior to the onset of stationary phase. Aflatoxin B1 was first detected approximately 8 h after the appearance of the ver-1 and nor-1 transcripts. In contrast, maximum transcript accumulation for the pyrG gene (encoding orotidine monophosphate decarboxylase), which is involved in primary metabolism, was observed at the onset of trophophase when the ver-1 and nor-1 transcripts could not be detected. Accumulation of the ver-1 and nor-1 transcripts was also studied following a nutritional shift from a non-aflatoxin-supporting medium (peptone mineral salts [PMS]) to a glucose-containing medium (glucose mineral salts [GMS]), which does support aflatoxin biosynthesis. Transcripts from ver-1 and nor-1 could not be detected on PMS medium but did accumulate approximately 4 to 7 h following transfer to GMS medium. Additionally, aflatoxins were not detected in PMS medium but were observed to accumulate within 24 h after the shift from PMS to GMS. These data suggest that aflatoxin biosynthesis is in part regulated by the accumulation of the ver-1 and nor-1 transcripts.

The metabolic burden of cellulase expression by recombinant Saccharomyces cerevisiae Y294 in aerobic batch culture

Abstract: Two recombinant strains of Saccharomyces cer- evisiae Y294 producing cellulase using different expression strategies were compared to a reference strain in aerobic culture to evaluate the potential metabolic burden that cel- lulase expression imposed on the yeast metabolism. In a chemically defined mineral medium with glucose as carbon source, S. cerevisiae strain Y294(CEL5) with plasmid-borne cellulase genes produced endoglucanase and β-glucosidase activities of 0.038 and 0.30 U mg dry cell weight −1 , respec- tively. Chromosomal expression of these two cellulases in strain Y294(Y118p) resulted in no detectable activity, al- though low levels of episomally co-expressed cellobiohy- drolase (CBH) activity were detected. Whereas the biomass concentration of strain Y294(CEL5) was slightly greater than that of a reference strain, CBH expression by Y294 (Y118p) resulted in a 1.4-fold lower maximum specific growth rate than that of the reference. Supplementation of the growth medium with amino acids significantly improved culture growth and enzyme production, but only partially mitigated the physiological effects and metabolic burden of cellulase expression. Glycerol production was decreased significantly, up to threefold, in amino acid-supplemented cultures, apparently due to redox balancing. Disproportion- ately higher levels of glycerol production by Y294(CEL5) indicated a potential correlation between the redox balance of anabolism and the physiological stress of cellulase pro- duction. With the reliance on cellulase expression in yeast for the development of consolidated bioprocesses for bio- ethanol production, this work demonstrates the need for development of yeasts that are physiologically robust in response to burdens imposed by heterologous enzyme production.

Regulation of Periplasmic Carbonic Anhydrase Expression in Chlamydomonas reinhardtii by Acetate and pH

Abstract: The effects of mixotrophic growth with acetate and growth medium pH on expression of extracellular carbonic anhydrase (CA) in Chlamydomonas reinhardtii were evaluated. Addition of 10 mM acetate to the culture medium resulted in reduction of CA activity that was parallel to the reduction generated by growth of the algae in high external CO2 concentrations. This reduction in activity is a consequence of lower level of the CA protein as determined by western analysis. Transcript abundance of cah-1, the gene encoding the low CO2-induced CA, is also reduced by the addition of acetate as verified by northern analysis. Measurements of photosynthesis and respiration suggest that the acetate-induced reduction of CA expression is not a function of lowered photosynthetic capacity, but may be the result of increased internal CO2 concentration generated by high, acetate-stimulated respiratory rates. Growth medium pH can also influence extracellular CA expression. The induction of CA activity, protein abundance, and transcript levels by exposure to limiting inorganic carbon (Ci) concentrations is much more pronounced at higher than at lower pH values. The relationship between pH regulation of CA expression and its role in the Ci-concentrating mechanism are discussed.