Aerobic and anaerobic cellulase production by Cellulomonas uda

Abstract

Cellulomonas uda (DSM 20108/ATCC 21399) is one of the few described cellulolytic facultative anaerobes. Based on these characteristics, we initiated a physiological study of C. uda with the aim to exploit it for cellulase production in simple bioreactors with no or sporadic aeration. Growth, cellulase activity and fermentation product formation were evaluated in different media under both aerobic and anaerobic conditions and in experiments where C. uda was exposed to alternating aerobic/anaerobic growth conditions. Here we show that C. uda behaves as a true facultative anaerobe when cultivated on soluble substrates such as glucose and cellobiose, but for reasons unknown cellulase activity is only induced under aerobic conditions on insoluble cellulosic substrates and not under anaerobic conditions. These findings enhance knowledge on the limited number of described facultative cellulolytic anaerobes, and in addition it greatly limits the utility of C. uda as an 'easy to handle' cellulase producer with low aeration demands.

Keywords: Aerobic/anaerobic; Cellulase; Cellulomonas uda; Cellulose degradation; Facultative anaerobe.

Fig. 1

Aerobic growth of C. uda on α-cellulose (20 g l⁻¹). Plotted are the FPA, CDW (calculated from the assimilated ammonium) and ammonium concentrations in the cultures. FPA levels below the detection limit are shown as zero. Symbols: (open circle) CDW, (open square) FPA and (plus sign) NH₄ ⁺

Fig. 2

Concentrations of fermentation products and CDW in cultures of C. uda grown on α-cellulose (20 g l⁻¹) under aerobic conditions (a) or under aerobic conditions for the first 36 h, followed by anaerobic conditions (b). The broken vertical line in (b) indicates the switch to anaerobic conditions. The experiment is the same as in Fig. 3. Symbols: (open square) Formic acid, (open diamond) Acetic acid, (open triangle) Lactic acid, (multiple sign) Succinic acid, (plus sign) Ethanol and (open circle) CDW

Fig. 3

CDW (calculated from ammonium assimilation) and FPA levels in cultures of C. uda grown on α-cellulose (20 g l⁻¹) under aerobic conditions (‘Aerobic’) or grown under aerobic conditions for the first 36 h, followed by anaerobic conditions (‘Anaerobic’). The broken vertical line indicates the switch to anaerobic conditions in ‘Anaerobic’. FPA levels below the detection limit are shown as zero. The experiment is the same as in Fig. 2. Symbols: (open circle) CDW ‘Aerobic’, (filled circle) CDW ‘Anaerobic’, (open square) FPA ‘Aerobic’ and (filled square) FPA ‘Anaerobic’

Fig. 4

FPA and EGA levels in cultures grown on α-cellulose (20 g l⁻¹) under anaerobic conditions (labelled ‘Anaerobic’) or under initially anaerobic conditions followed by aerobic conditions (labelled ‘Aerobic’). The broken vertical line indicates the switch to aerobic conditions in ‘Aerobic’ at 72 h. FPA levels below the detection limit are shown as zero. Symbols: (open square) FPA ‘Aerobic’, (filled square) FPA ‘Anaerobic’, (open triangle) EGA ‘Aerobic’ and (filled triangle) EGA ‘Anaerobic’

Fig. 5

CDW and FPA levels in C. uda cultures initially grown aerobically on glucose as the initial substrate (5 g l⁻¹). After 48 h (first vertical dotted line), the gas phase of all cultures was replaced with N₂. After 72 h (second vertical dotted line), α-cellulose (10 g l⁻¹) was added to all cultures and the gas phase of ‘Aerobic’ was reverted to atmospheric air, while ‘Anaerobic’ remained anaerobic. FPA levels below the detection limit are shown as zero. Symbols: (open circle) CDW ‘Aerobic’, (filled circle) CDW ‘Anaerobic’, (open square) FPA ‘Aerobic’ and (filled square) FPA ‘Anaerobic’

Fig. 6

EGA levels in C. uda cultures initially grown aerobically on glucose as the initial substrate (5 g l⁻¹). After 48 h (first vertical dotted line), the gas phase of all cultures was replaced with N₂. After 72 h (second vertical dotted line), α–cellulose (10 g l⁻¹) was added to all cultures and the gas phase of ‘Aerobic’ was reverted to atmospheric air, while ‘Anaerobic’ remained anaerobic. Same experiment as in Fig. 5. Symbols: (open triangle) EGA ‘Aerobic’ and (filled triangle) EGA ‘Anaerobic’