124
et al. 2002; Garcia-Gonzalez and De Wever 2018). However, significant impact was
seen on the polyhydroxyalkanoates composition: Cupriavidus necator was shown
to produce a high polyhydroxybutyrate-co-valerate content with a 10–20 g/L feed of
glucose (Możejko-Ciesielska and Kiewisz 2016), while it produced almost pure
polyhydroxybutyrate under the presence of CO gas (Volova et al. 2002). Moreover,
it can alternate between heterotrophic and autotrophic biosynthesis of polyhydroxyalkanoates or combine both modes.
Effect on Polyhydroxyalkanoates Production and Storage
For mixed cultures, limited studies have investigated systematically the influence of
substrate composition on polyhydroxyalkanoates yield, in part because microbial
mixed cultures vary as the substrate is altered, and hence studies typically focus on
a particular substrate application. In a comparison of acetate and propionate as substrate, it was found the former led to higher polyhydroxyalkanoates storage (Lemos
et al. 2006). In a separate study by Wang et al. investigating the combined role of
dissolved oxygen and substrate with a microbial mixed culture, it was concluded
that butyrate and valerate were consumed faster than acetic and propionic acids
(Wang et al. 2017) under both high and low dissolved oxygen levels. It was also
shown these two substrates were less affected by dissolved oxygen concentration,
demonstrating interactions between various operational parameters and that low
dissolved oxygen levels can be used with butyrate and valerate substrates, which
will lower the costs of polyhydroxyalkanoates production. A few other studies have
evaluated polyhydroxyalkanoates production by mixed cultures using other substrates such as butyrate, ethanol, glucose, malate, and others (Morgan-Sagastume
et al. 2015; Duque et al. 2014; Cui et al. 2016). Duque et al. evaluated polyhydroxyalkanoates production by microbial mixed cultures using three types of wastes.
Synthetic wastewater, which contained 68% acetate, 26% butyrate, 3% propionate,
and 2% valerate; fermented sugarcane molasses, with a 38% propionate, 32% acetate, and 15% of valerate and butyrate content; and fermented cheese whey, with a
content of 68% acetate, 21% butyrate, 8% propionate, and 3% lactate, were used to
accumulate polyhydroxyalkanoates in microbial mixed cultures under the same
conditions. The highest polyhydroxyalkanoates accumulation was achieved by fermented cheese whey reaching 65% cell dry weight, followed by fermented sugarcane waste that achieved a polyhydroxyalkanoates accumulation of 56% cell dry
weight, while the synthetic wastewater resulted in an accumulation of 52% cell dry
weight (Duque et al. 2014). Tamang et al. tested polyhydroxyalkanoates accumulation of a microbial mixed culture using acetate and acidified brewery wastewater
under similar conditions. Acetate resulted in a higher polyhydroxybutyrate storage
at 72.6% cell dry weight, while the wastewater resulted in 44.8% cell dry weight
accumulation (Tamang et al. 2019). Complex substrates such as municipal wastewater and meat extract resulted in much lower accumulation of 15 and 13% cell dry
weight, respectively, compared to values in the region of 40% cell dry weight
achieved using acetate or propionate in the same study (Yuan et al. 2015). Therefore,
S. Sali and H. R. Mackey
et al. 2002; Garcia-Gonzalez and De Wever 2018). However, significant impact was
seen on the polyhydroxyalkanoates composition: Cupriavidus necator was shown
to produce a high polyhydroxybutyrate-co-valerate content with a 10–20 g/L feed of
glucose (Możejko-Ciesielska and Kiewisz 2016), while it produced almost pure
polyhydroxybutyrate under the presence of CO gas (Volova et al. 2002). Moreover,
it can alternate between heterotrophic and autotrophic biosynthesis of polyhydroxyalkanoates or combine both modes.
Effect on Polyhydroxyalkanoates Production and Storage
For mixed cultures, limited studies have investigated systematically the influence of
substrate composition on polyhydroxyalkanoates yield, in part because microbial
mixed cultures vary as the substrate is altered, and hence studies typically focus on
a particular substrate application. In a comparison of acetate and propionate as substrate, it was found the former led to higher polyhydroxyalkanoates storage (Lemos
et al. 2006). In a separate study by Wang et al. investigating the combined role of
dissolved oxygen and substrate with a microbial mixed culture, it was concluded
that butyrate and valerate were consumed faster than acetic and propionic acids
(Wang et al. 2017) under both high and low dissolved oxygen levels. It was also
shown these two substrates were less affected by dissolved oxygen concentration,
demonstrating interactions between various operational parameters and that low
dissolved oxygen levels can be used with butyrate and valerate substrates, which
will lower the costs of polyhydroxyalkanoates production. A few other studies have
evaluated polyhydroxyalkanoates production by mixed cultures using other substrates such as butyrate, ethanol, glucose, malate, and others (Morgan-Sagastume
et al. 2015; Duque et al. 2014; Cui et al. 2016). Duque et al. evaluated polyhydroxyalkanoates production by microbial mixed cultures using three types of wastes.
Synthetic wastewater, which contained 68% acetate, 26% butyrate, 3% propionate,
and 2% valerate; fermented sugarcane molasses, with a 38% propionate, 32% acetate, and 15% of valerate and butyrate content; and fermented cheese whey, with a
content of 68% acetate, 21% butyrate, 8% propionate, and 3% lactate, were used to
accumulate polyhydroxyalkanoates in microbial mixed cultures under the same
conditions. The highest polyhydroxyalkanoates accumulation was achieved by fermented cheese whey reaching 65% cell dry weight, followed by fermented sugarcane waste that achieved a polyhydroxyalkanoates accumulation of 56% cell dry
weight, while the synthetic wastewater resulted in an accumulation of 52% cell dry
weight (Duque et al. 2014). Tamang et al. tested polyhydroxyalkanoates accumulation of a microbial mixed culture using acetate and acidified brewery wastewater
under similar conditions. Acetate resulted in a higher polyhydroxybutyrate storage
at 72.6% cell dry weight, while the wastewater resulted in 44.8% cell dry weight
accumulation (Tamang et al. 2019). Complex substrates such as municipal wastewater and meat extract resulted in much lower accumulation of 15 and 13% cell dry
weight, respectively, compared to values in the region of 40% cell dry weight
achieved using acetate or propionate in the same study (Yuan et al. 2015). Therefore,
S. Sali and H. R. Mackey