Nesterenkonia sp. strain F, a halophilic bacterium producing acetone, butanol, and ethanol under aerobic conditions

Abstract

The moderately halophilic bacterium Nesterenkonia sp. strain F, which was isolated from Aran-Bidgol Lake (Iran), has the ability to produce acetone, butanol, and ethanol (ABE) as well as acetic and butyric acids under aerobic and anaerobic conditions. This result is the first report of ABE production with a wild microorganism from a family other than Clostridia and also the first halophilic species shown to produce butanol under aerobic cultivation. The cultivation of Nesterenkonia sp. strain F under anaerobic conditions with 50 g/l of glucose for 72 h resulted in the production of 105 mg/l of butanol, 122 mg/l of acetone, 0.2 g/l of acetic acid, and 2.5 g/l of butyric acid. Furthermore, the strain was cultivated on media with different glucose concentrations (20, 50, and 80 g/l) under aerobic and anaerobic conditions. Through fermentation with a 50 g/l initial glucose concentration under aerobic conditions, 66 mg/l of butanol, 125 mg/l of acetone, 291 mg/l of ethanol, 5.9 g/l of acetic acid, and 1.2 g/l of butyric acid were produced. The enzymes pertaining to the fermentation pathway in the strain were compared with the enzymes of Clostridium spp., and the metabolic pathway of fermentation used by Nesterenkonia sp. strain F was investigated.

Figure 1. Concentrations of fermentation products, i.e., butanol (black), acetone (dark gray), ethanol (white), acetic acid, and butyric acid (light gray), as well as consumed glucose (light gray) detected through the fermentation of glucose with an initial concentration of 50 g/l at 37 °C under anaerobic conditions for 48 (dashed border) and 72 h (solid border).

Figure 2. Concentrations of fermentation products, i.e., butanol (black), acetone (dark gray), ethanol (white), acetic acid, and butyric acid (light gray), as well as consumed glucose (light gray) obtained through fermentation of glucose with initial concentration of 20 (a,d), 50 (b,e), and 80 g/l (c,f) at 32 °C under aerobic (a–c) and anaerobic conditions (d–f) for 48 (dashed border) and 72 h (solid border).

Figure 3. Subsystem category distribution of Nesterenkonia sp. strain F encoding genes.

Figure 4. Catabolic pathways used by solvent-producing Clostridia.

The directions of carbon and electron flow are shown by black and blue arrows, respectively. Enzymes indicated by numbers are as follows: (1) glyceraldehyde-3-phosphate dehydrogenase, (2) pyruvate-ferredoxin oxidoreductase, (3) NADH-ferredoxin oxidoreductase, (4) NADPH-ferredoxin oxidoreductase, (5) hydrogenase, (6) lactate dehydrogenase, (7) phosphate acetyltransferase (phosphotransacetylase), (8) acetate kinase, (9) thiolase (acetyl-CoA acetyltransferase), (10) 3-hydroxybutyryl-CoA dehydrogenase, (11) crotonase, (12) butyryl-CoA dehydrogenase, (13) phosphate butyltransferase (phosphotransbutyrylase), (14) butyrate kinase, (15) acetaldehyde dehydrogenase, (16) ethanol dehydrogenase, (17) butyraldehyde dehydrogenase, (18) butanol dehydrogenase, (19) acetoacetyl-CoA: acetate/butyrate: CoA transferase, (20) acetoacetate decarboxylase, and (21) pyruvate dehydrogenase.