Page 52 - Refining Biomass Residues for Sustainable Energy and Bioproducts

30 Refining Biomass Residues for Sustainable Energy and Bioproducts

negligible substrate toxicity (Hetzler and Steinbu ¨chel, 2013). Previously reported
oleaginous bacterium Arthrobacter AK19 also stores lipids in a similar fashion, but
this strain has not been applied for further studies (Ro ¨ttig and Steinbu ¨chel, 2016).
Utilization of industrial wastes, such as molasses, agro-industrial waste, dairy
waste, or lignocellulosic hydrolysates by Rhodococcus or Gordonia strain and cello-
biose by Streptomyces isolate for the production of lipids, is also reported
(Table 2.1). The TAG synthesized by Rhodococcus is majorly composed of straight
chain fatty acid residues having carbon range between C 16 and C 18 , while
Streptomycetes are able to add branched chain fatty acids (Alvarez et al., 1996;
Olukoshi and Packter, 1994). It is imperative to know that fatty acid contents are
generally measured in batch culture, while a continuous culture could significantly
enhance the overall fatty acid productivity. However, only higher lipid accumula-
tion would not make the process cost-effective, as the total yield might be compara-
bly low as, for example, even though the yield of lipid after batch culture of R.
opacus cells with molasses as carbon source was described to be 92% of CDW,
only approximate 55 mg/L, equivalent to a yield of 0.6 mg/L/h was achieved
(Gouda et al., 2008). In contrast, with a 30 L fed-batch culture of R. opacus having
molasses and sucrose as carbon source, the yield was considerably enhanced to
19.4 g/L or 0.38 g/L/h, and the percentage yield was observed around 50% of its
CDW (Voss and Steinbu ¨chel, 2001). Thus the yields of batch cultivation and the
fed-batch cultivation are not essentially same. Accumulation of intracellular FFA
up to 25% of CDW by bacterial strain Catenisphaera adipataccumulans GK12 was
reported though a unique mechanism (Katayama et al., 2014). Nevertheless, it is
debatable that lower concentration of FFA is toxic for cells still a microbe can store
it as reserve lipid granules. On the other hand, during processing of cell biomass,
the stored lipids could detach from FFA as well. Moreover, Streptomyces sp. NP10
has been reported to secrete good amount of FFA having a complex nature when
cultured in a complex medium (IlicTomic et al., 2015). The activated sludge
obtained from anoxic tank of wastewater treatment plants typically showed a higher
fraction of Actinomycetes. This multifarious consortium of oleaginous microbes
could be possibly applied for the extraction of lipids for biodiesel production
(Muller et al., 2014; Kumar et al., 2016c).

2.3.2 Production of lipids and triacylglycerol from Gram-
negative bacteria
Gram-negative bacterial strains have not been much reported to accumulate TAG as
compared to Gram-positive bacteria. In spite of this, few Gram-negative bacterial
strains belonging to Acinetobacter or hydrocarbonoclastic group such as
Alcanivorax or Marinobacter sp. are capable to synthesize WE, which are com-
monly stored as mixed lipid inclusion bodies along with a small quantity of TAG,
Table 2.2. Remarkable quantities are produced, when these bacterial strains are
grown on certain carbon sources, such as n-alkanes or olive oil (Ishige et al., 2003;
Alvarez et al., 1997b). A Gram-negative strain, Aeromonas sp. 3010, succeeded a
total fatty acid content of about 12% CDW, 30% of which is eicosapentaenoic acid