Ethanol Catabolism in <i>Corynebacterium glutamicum</i>

Abstract

Corynebacterium glutamicum grows on a variety of carbohydrates and organic acids as single or combined sources of carbon and energy. Here we show the ability of C. glutamicum to grow on ethanol with growth rates up to 0.24 h^–1 and biomass yields up to 0.47 g dry weight (g ethanol)^–1. Mutants of C. glutamicum deficient in phosphotransacetylase (PTA), isocitrate lyase (ICL) and malate synthase (MS) were unable to grow on ethanol, indicating that acetate activation and the glyoxylate cycle are essential for utilization of this substrate. In accordance, the expression profile of ethanol-grown C. glutamicum cells compared to that of glucose-grown cells revealed an increased expression of genes encoding acetate kinase (AK), PTA, ICL and MS. Furthermore, the specific activities of these four enzymes as well as those of alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) were found to be high in ethanol-grown and low in glucose-grown cells. Growth of C. glutamicum on a mixture of glucose and ethanol led to a biphasic growth behavior, which was due to the sequential utilization of glucose before ethanol. Accordingly, the specific activities of ADH, ALDH, AK, PTA, ICL and MS in cells grown in medium containing both substrates were as low as in glucose-grown cells in the first growth phase, but increased 5- to 100-fold during the second growth phase. The results indicate that ethanol catabolism in C. glutamicum is subject to carbon source-dependent regulation, i.e., to a carbon catabolite control.

Arabitol Metabolism of Corynebacterium glutamicum and Its Regulation by AtlR

“…The simultaneous consumption of two substrates and the monophasic growth of C. glutamicum with glucose or other sugars and with glucose and additional organic acids, such as lactate, pyruvate, acetate, and propionate, were shown previously (18,20,23,32,47,54,56,69,75). Diauxic growth and the sequential utilization of carbon sources by C. glutamicum have been described only for mixtures of glucose and glutamate (45,48) and for mixtures of glucose and ethanol (3,4,44). In both cases, C. glutamicum consumes glucose in the first growth phase and consumes the other substrate in the second growth phase, due to the carbon catabolite repression of the glutamate uptake system (gluABCD cluster) or of the ADH and ALDH genes (adhA and ald), respectively, in the presence of glucose (2,44,48).…”

“…The organism can use a variety of sugars (e.g., glucose, fructose, sucrose, ribose, or maltose) and organic acids (acetate, propionate, pyruvate, lactate, or citrate) as single or combined carbon and energy sources for growth and also for amino acid production. C. glutamicum is also able to use ethanol as a sole carbon and energy source, using alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) for NAD-dependent oxidations to acetate, which is then activated to acetyl coenzyme A (acetyl-CoA) and channeled into the citric acid and glyoxylate cycles (2,4,5,44). The ADH gene (adhA) of C. glutamicum has been shown to be subject to complex, carbon source-dependent regulation by the global transcriptional regulators RamA, RamB, and GlxR (2,6,43).…”

The Alcohol Dehydrogenase Gene adhA in Corynebacterium glutamicum Is Subject to Carbon Catabolite Repression

“…In contrast to the growth of C. glutamicum on many substrate mixtures, such as glucose plus acetate, lactate, pyruvate, or fructose (7,12,52), the growth of this organism on a mixture of glucose and ethanol is biphasic, with glucose consumption in the first and ethanol consumption in the second exponential growth phase (3). This biphasic growth behavior is probably due to relatively low ADH and ALDH activities in the first and much higher ADH and ALDH activities (and thus, high ethanol oxidation activity) in the second growth phase (3).…”

“…This substrate is oxidized via acetaldehyde to acetate, which enters the tricarboxylic acid cycle after activation to acetyl coenzyme A (acetyl-CoA). As in the case of the growth of C. glutamicum with acetate as the sole carbon source, the glyoxylate cycle plays an essential role in the anaplerotic function during growth on ethanol (3). Whereas the acetate-activating enzymes acetate kinase (AK) and phosphotransacetylase (PTA) and, also, the key enzymes of the glyoxylate cycle, isocitrate lyase (ICL) and malate synthase (MS) and their respective genes (ack, pta, aceA, and aceB) have been intensively investigated (reviewed in reference 20), much less is known about the alcohol and acetaldehyde dehydrogenases (ADH and ALDH, respectively), which are involved in ethanol's oxidation to acetate.…”

“…This biphasic growth behavior is probably due to relatively low ADH and ALDH activities in the first and much higher ADH and ALDH activities (and thus, high ethanol oxidation activity) in the second growth phase (3). Diauxic growth of C. glutamicum and the sequential utilization of carbon sources have been reported so far only for its growth in medium containing glucose and glutamate, and here the biphasic growth behavior is due to the repression of the glutamate uptake system in the presence of glucose (32,33).…”