occurring, biofilm-forming Bacillus-Aspergillus community which demonstrated
synergistic behavior when grown on hexadecane or crude oil (Perera et al. pers.
comm.), as the sole source of carbon, where the degradation percentage by the
biofilm was higher within the test period than achieved by the sum of the degradation
by individual organisms.
Conversely, some other combinations of microbes may interact antagonistically;
e.g., Burkholderia, Paraburkholderia, and Thauera were found to have negative
correlations in activated sludge during petroleum hydrocarbon degradation, while
Burkholderia, Paraburkholderia and Luteibactor, as well as Flavobacerium and
Aquabacterium were found to have positive mutual correlations (Cui et al. 2019).
Careful selection of microbial species is therefore warranted in developing a
system for biodegradation.
11.7.2 Immobilization of Microbes
Immobilization of microbes is an important technology in bioremediation strategies
as it helps to maintain a high biomass. In open mobile systems such as oceans, the
hydrocarbanoclastic microorganisms may be lost from the site due to dispersion and
the free flow of water. Immobilization techniques are used to retain the microbes at
the site of contamination and have many added advantages such as providing a
suitable protective microenvironment for the survival of microorganisms as well as
allowing cell reuse, thus reducing costs. They have also been shown to provide
resistance to toxic chemicals, pH, temperature, etc. and provide genetic stability of
the microorganisms (Bayat et al. 2015).
Supportive carriers for immobilization are of two types, namely organic and
inorganic. Organic carriers may be natural or synthetic. Examples of natural carriers
include agar, agarose, and chitin while acrylamide, polyurethane, polyvinyl, and
resins are some synthetic carriers that are used for immobilization. Inorganic carriers
may be compounds like clay, activated charcoal, or ceramics (Bayat et al. 2015).
Various techniques are used to immobilize microbes onto the carriers. Recent
research (Chen et al. 2017) comparing free bacterial consortia with immobilized
consortia has shown that immobilization by embedded techniques improve the crude
oil degradation efficiency. A recent study tested the use of cinnamon and peanut
shells to embed and immobilize diesel degrading Pseudomonas YT strain (Fu et al.
2019). Their study indicated that cinnamon shells were more suitable for immobilization. A sodium alginate-calcium chloride (calcium alginate) biocarrier has been
used and performance improved with the addition of activated carbon in the embedding (Chen et al. 2017).
Naturally formed biofilms as previously reported (Perera et al. 2019) may also
prove to be an useful alternative where ex situ remediation is carried out in a
remediation plant.
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281
synergistic behavior when grown on hexadecane or crude oil (Perera et al. pers.
comm.), as the sole source of carbon, where the degradation percentage by the
biofilm was higher within the test period than achieved by the sum of the degradation
by individual organisms.
Conversely, some other combinations of microbes may interact antagonistically;
e.g., Burkholderia, Paraburkholderia, and Thauera were found to have negative
correlations in activated sludge during petroleum hydrocarbon degradation, while
Burkholderia, Paraburkholderia and Luteibactor, as well as Flavobacerium and
Aquabacterium were found to have positive mutual correlations (Cui et al. 2019).
Careful selection of microbial species is therefore warranted in developing a
system for biodegradation.
11.7.2 Immobilization of Microbes
Immobilization of microbes is an important technology in bioremediation strategies
as it helps to maintain a high biomass. In open mobile systems such as oceans, the
hydrocarbanoclastic microorganisms may be lost from the site due to dispersion and
the free flow of water. Immobilization techniques are used to retain the microbes at
the site of contamination and have many added advantages such as providing a
suitable protective microenvironment for the survival of microorganisms as well as
allowing cell reuse, thus reducing costs. They have also been shown to provide
resistance to toxic chemicals, pH, temperature, etc. and provide genetic stability of
the microorganisms (Bayat et al. 2015).
Supportive carriers for immobilization are of two types, namely organic and
inorganic. Organic carriers may be natural or synthetic. Examples of natural carriers
include agar, agarose, and chitin while acrylamide, polyurethane, polyvinyl, and
resins are some synthetic carriers that are used for immobilization. Inorganic carriers
may be compounds like clay, activated charcoal, or ceramics (Bayat et al. 2015).
Various techniques are used to immobilize microbes onto the carriers. Recent
research (Chen et al. 2017) comparing free bacterial consortia with immobilized
consortia has shown that immobilization by embedded techniques improve the crude
oil degradation efficiency. A recent study tested the use of cinnamon and peanut
shells to embed and immobilize diesel degrading Pseudomonas YT strain (Fu et al.
2019). Their study indicated that cinnamon shells were more suitable for immobilization. A sodium alginate-calcium chloride (calcium alginate) biocarrier has been
used and performance improved with the addition of activated carbon in the embedding (Chen et al. 2017).
Naturally formed biofilms as previously reported (Perera et al. 2019) may also
prove to be an useful alternative where ex situ remediation is carried out in a
remediation plant.
11 Microbial Bioremediation of Petroleum Hydrocarbons
281