dorsal/arxiv
View SchemaIdentification of the growth-limiting step in continuous cultures from initial rates measured in response to substrate-excess conditions
| Authors | Jason T. Noel, Brenton Cox, Atul Narang |
|---|---|
| Categories | |
| ArXiv ID | q-bio/0509013 |
| URL | https://arxiv.org/abs/q-bio/0509013 |
Abstract
When steady state chemostat cultures are abruptly exposed to substrate-excess conditions, they exhibit long lags before adjusting to the new environment. The identity of the rate-limiting step for this slow response can be inferred from the initial yields and specific growth rates measured by exposing steady state cultures at various dilution rates to substrate-excess conditions. We measured these parameters for glucose-limited cultures of E. coli ML308 growing at various dilution rates between 0.03 and 0.6 1/hr. In all the cases, the initial yields were 20-30% less than the steady state yields. The decline of the yield implies that overflow metabolism is triggered in response to excess glucose. It is therefore unlikely that the initial response of the cells is limited by substrate uptake. The initial specific growth rates of cultures growing at low dilution rates (D = 0.03, 0.05, 0.075, 0.1, 0.3 1/hr) were significantly higher than the steady state specific growth rates. However, the increment in the specific growth rate decreased with the dilution rate, and at D=0.6 1/hr, there was no improvement in the specific growth rate. The initial specific growth rates varied hyperbolically with the dilution, decreasing sharply at dilution rates below 0.1 1/hr and saturating at D=0.6 1/hr. This is consistent with a picture in which the initial response is limited by the activity of glutamate dehydrogenase.
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"abstract": "When steady state chemostat cultures are abruptly exposed to substrate-excess\nconditions, they exhibit long lags before adjusting to the new environment. The\nidentity of the rate-limiting step for this slow response can be inferred from\nthe initial yields and specific growth rates measured by exposing steady state\ncultures at various dilution rates to substrate-excess conditions. We measured\nthese parameters for glucose-limited cultures of E. coli ML308 growing at\nvarious dilution rates between 0.03 and 0.6 1/hr. In all the cases, the initial\nyields were 20-30% less than the steady state yields. The decline of the yield\nimplies that overflow metabolism is triggered in response to excess glucose. It\nis therefore unlikely that the initial response of the cells is limited by\nsubstrate uptake. The initial specific growth rates of cultures growing at low\ndilution rates (D = 0.03, 0.05, 0.075, 0.1, 0.3 1/hr) were significantly higher\nthan the steady state specific growth rates. However, the increment in the\nspecific growth rate decreased with the dilution rate, and at D=0.6 1/hr, there\nwas no improvement in the specific growth rate. The initial specific growth\nrates varied hyperbolically with the dilution, decreasing sharply at dilution\nrates below 0.1 1/hr and saturating at D=0.6 1/hr. This is consistent with a\npicture in which the initial response is limited by the activity of glutamate\ndehydrogenase.",
"arxiv_id": "q-bio/0509013",
"authors": [
"Jason T. Noel",
"Brenton Cox",
"Atul Narang"
],
"categories": [
"q-bio.MN"
],
"title": "Identification of the growth-limiting step in continuous cultures from initial rates measured in response to substrate-excess conditions",
"url": "https://arxiv.org/abs/q-bio/0509013"
},
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