134
with pure acetate (De Grazia et al. 2017). A similar experiment conducted on microbial mixed cultures observed that polyhydroxyalkanoates accumulation rate reduced
as the temperature increased (Krishna and Van Loosdrecht 1999). Similar trends
were later reported by Jiang et al. using a microbial mixed culture as well (Jiang
et al. 2011c). Johnson evaluated the impact of temperature in a short-term and longterm fermenter. The temperature was varied from 15 to 35 °C in a sequencing batch
reactor with a feast-famine mode to monitor short-term effects. The study concluded
that there was a little variation in polyhydroxyalkanoates production in the fermenter with short-term feeding and temperatures ranging from 20 to 35 °C. However, a
low temperature of 15 °C resulted in the highest polyhydroxyalkanoates production.
However, for the long-term feeding operated fermenter, the highest polyhydroxyalkanoates production was achieved at 30 °C, as a result of a change in the microbial
community (Johnson et al. 2009b). The new community at higher temperatures had
much more rapid conversion of substrate and longer famine periods than at the
lower temperature steady states. Jiang et al. investigated the effects of temperature
on polyhydroxybutyrate production under feast-famine conditions. They conducted
the experiment on Zoogloea and Plasticicumulans acidivorans bacteria in the range
of 20 to 30 °C in separate batches. Both bacteria produced more than 75% polyhydroxyalkanoates cell dry weight at the optimal condition of 20 and 30 °C for
Zoogloea and Plasticicumulans acidivorans, respectively (Jiang et al. 2011c).
Temperature is therefore highly dependent on culture and the selected organism(s)
responsible for polyhydroxyalkanoates production.
5.4.8 Light Impact
Sunlight functions as an energy source to drive carbon conversion, whether autotrophically from CO 2 or heterotrophically from organic carbon feedstocks for oxygenic and anoxygenic phototrophs, respectively. Photosynthetic bacteria are
explored as a means to reduce costs associated with aeration (Fradinho et al. 2013b)
by utilizing abundant availability of sunlight to supply energy for carbon conversion. Light-dark cycling is reported to regulate the accumulation of polyhydroxyalkanoates in some types of bacteria under anoxygenic or anaerobic conditions,
whereby carbon is stored during photosynthesis and then consumed for energy during dark hours (Saharan et al. 2014; Fradinho et al. 2013b).
Cyanobacteria, such as Arthrospira (formerly known as Spirulina), are known
photosynthetic bacteria with the ability to produce polyhydroxyalkanoates (Chee
et al. 2010). Synechococcus was able to produce up to 55% polyhydroxyalkanoates
of cell dry weight under phosphate-limiting conditions, whereas, Synechocystis was
able to accumulate 15% of polyhydroxyalkanoates of cell dry weight under nitrogenlimiting conditions (Saharan et al. 2014). It was discovered that one of the best triggers for polyhydroxyalkanoates accumulation in cyanobacteria is nutrient-limiting
conditions because nitrogen-depleted cells do not have the ability to synthesize proteins needed for reproduction, which triggers the accumulation of
S. Sali and H. R. Mackey
with pure acetate (De Grazia et al. 2017). A similar experiment conducted on microbial mixed cultures observed that polyhydroxyalkanoates accumulation rate reduced
as the temperature increased (Krishna and Van Loosdrecht 1999). Similar trends
were later reported by Jiang et al. using a microbial mixed culture as well (Jiang
et al. 2011c). Johnson evaluated the impact of temperature in a short-term and longterm fermenter. The temperature was varied from 15 to 35 °C in a sequencing batch
reactor with a feast-famine mode to monitor short-term effects. The study concluded
that there was a little variation in polyhydroxyalkanoates production in the fermenter with short-term feeding and temperatures ranging from 20 to 35 °C. However, a
low temperature of 15 °C resulted in the highest polyhydroxyalkanoates production.
However, for the long-term feeding operated fermenter, the highest polyhydroxyalkanoates production was achieved at 30 °C, as a result of a change in the microbial
community (Johnson et al. 2009b). The new community at higher temperatures had
much more rapid conversion of substrate and longer famine periods than at the
lower temperature steady states. Jiang et al. investigated the effects of temperature
on polyhydroxybutyrate production under feast-famine conditions. They conducted
the experiment on Zoogloea and Plasticicumulans acidivorans bacteria in the range
of 20 to 30 °C in separate batches. Both bacteria produced more than 75% polyhydroxyalkanoates cell dry weight at the optimal condition of 20 and 30 °C for
Zoogloea and Plasticicumulans acidivorans, respectively (Jiang et al. 2011c).
Temperature is therefore highly dependent on culture and the selected organism(s)
responsible for polyhydroxyalkanoates production.
5.4.8 Light Impact
Sunlight functions as an energy source to drive carbon conversion, whether autotrophically from CO 2 or heterotrophically from organic carbon feedstocks for oxygenic and anoxygenic phototrophs, respectively. Photosynthetic bacteria are
explored as a means to reduce costs associated with aeration (Fradinho et al. 2013b)
by utilizing abundant availability of sunlight to supply energy for carbon conversion. Light-dark cycling is reported to regulate the accumulation of polyhydroxyalkanoates in some types of bacteria under anoxygenic or anaerobic conditions,
whereby carbon is stored during photosynthesis and then consumed for energy during dark hours (Saharan et al. 2014; Fradinho et al. 2013b).
Cyanobacteria, such as Arthrospira (formerly known as Spirulina), are known
photosynthetic bacteria with the ability to produce polyhydroxyalkanoates (Chee
et al. 2010). Synechococcus was able to produce up to 55% polyhydroxyalkanoates
of cell dry weight under phosphate-limiting conditions, whereas, Synechocystis was
able to accumulate 15% of polyhydroxyalkanoates of cell dry weight under nitrogenlimiting conditions (Saharan et al. 2014). It was discovered that one of the best triggers for polyhydroxyalkanoates accumulation in cyanobacteria is nutrient-limiting
conditions because nitrogen-depleted cells do not have the ability to synthesize proteins needed for reproduction, which triggers the accumulation of
S. Sali and H. R. Mackey