Specifically, microbial biosurfactants may also be classified by their producers.
Bacteria, e.g., Pseudomonas, Bacillus, Acinetobacter, Rhodococcus; and fungi, e.g.,
Candida and Saccharomyces are the most frequently mentioned biosurfactantproducing microbial strains as reviewed in detail previously (Pacwa-Płociniczak
et al. 2011; de Cássia et al. 2014).
24.2.2 Synthetic Surfactants vs. Biosurfactants
The advantages of synthetic surfactants are their availability via synthesis, low costs,
and precisely defined chemical composition, all leading to their predictable effects. On
the other hand, their major disadvantage compared to biosurfactants is higher toxicity.
Another fundamental problem of biosurfactants is the inherently low yield of
bioprocesses required for their production, making their market prices relatively
high (Lau et al. 2014). In addition, some of their other properties rightly mentioned
above as benefits should at the same time be considered as potentially unfavorable.
Namely, their biodegradability usually leads to the necessity of periodical
biosurfactant additions in order to maintain their effective concentration within the
non-sterile processing medium (Maslin and Maier 2000). Also, significant variability
caused by rather small changes in the cultivation environment can be observed among
the batch cultivations, thus making the composition of the final product and its
properties less certain. However, there are many important inherent advantages of
biosurfactants, e.g., low toxicity, low CMC values, ecological acceptability, biodegradability, high selectivity, high yet specific activity at extreme temperatures, pH, and
salinity as reviewed elsewhere (Bustamante et al. 2012; Bezza and Chirwa 2015).
Several comparative studies stated either a minimal negative effect, if any, or
even a boost in cell growth and degradation activity by biosurfactants as opposed to
chemical surfactants. Solubilization and/or emulsification of biosurfactants were
also similar to those of their synthetic analogs, in many cases even higher. For
example, Sphingomonas sp. GF2B was able to mineralize up to 83.6% of
phenantrene (PHE) within 10 days without the addition of surfactants.
Biosurfactants facilitated PHE biodegradation to make it as high as 99.5%, whereas
the addition of Tween 80, conversely, inhibited the PHE biodegradation to merely
33.5% (Pei et al. 2010). Oil dispersion by several chemical surfactants and
biosurfactants with simultaneous bioremediation of a marine offshore oil spill was
studied by Pi et al. (2017). The results showed that the enhancement of petroleum
hydrocarbon bioremediation by rhamnolipids was twice as efficient compared to
commercial chemical dispersants, GM-2, without any toxic effect on microorganisms. Moreover, when assessing the effect of surfactant combination, a consistent
negative effect of GM-2 on rhamnolipids’ efficiency was observed.
Because of the above-mentioned disadvantages of synthetic surfactants, especially higher toxicity, low selectivity, and higher CMC values, their effective
eco-friendly replacement with biosurfactants is sought. However, synthetic surfactants remain dominant because of the disadvantages of biosurfactants, particularly
their high price (Lau et al. 2014). Thus, the most feasible cost-effective alternative to
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M. Halecký and E. Kozliak
Bacteria, e.g., Pseudomonas, Bacillus, Acinetobacter, Rhodococcus; and fungi, e.g.,
Candida and Saccharomyces are the most frequently mentioned biosurfactantproducing microbial strains as reviewed in detail previously (Pacwa-Płociniczak
et al. 2011; de Cássia et al. 2014).
24.2.2 Synthetic Surfactants vs. Biosurfactants
The advantages of synthetic surfactants are their availability via synthesis, low costs,
and precisely defined chemical composition, all leading to their predictable effects. On
the other hand, their major disadvantage compared to biosurfactants is higher toxicity.
Another fundamental problem of biosurfactants is the inherently low yield of
bioprocesses required for their production, making their market prices relatively
high (Lau et al. 2014). In addition, some of their other properties rightly mentioned
above as benefits should at the same time be considered as potentially unfavorable.
Namely, their biodegradability usually leads to the necessity of periodical
biosurfactant additions in order to maintain their effective concentration within the
non-sterile processing medium (Maslin and Maier 2000). Also, significant variability
caused by rather small changes in the cultivation environment can be observed among
the batch cultivations, thus making the composition of the final product and its
properties less certain. However, there are many important inherent advantages of
biosurfactants, e.g., low toxicity, low CMC values, ecological acceptability, biodegradability, high selectivity, high yet specific activity at extreme temperatures, pH, and
salinity as reviewed elsewhere (Bustamante et al. 2012; Bezza and Chirwa 2015).
Several comparative studies stated either a minimal negative effect, if any, or
even a boost in cell growth and degradation activity by biosurfactants as opposed to
chemical surfactants. Solubilization and/or emulsification of biosurfactants were
also similar to those of their synthetic analogs, in many cases even higher. For
example, Sphingomonas sp. GF2B was able to mineralize up to 83.6% of
phenantrene (PHE) within 10 days without the addition of surfactants.
Biosurfactants facilitated PHE biodegradation to make it as high as 99.5%, whereas
the addition of Tween 80, conversely, inhibited the PHE biodegradation to merely
33.5% (Pei et al. 2010). Oil dispersion by several chemical surfactants and
biosurfactants with simultaneous bioremediation of a marine offshore oil spill was
studied by Pi et al. (2017). The results showed that the enhancement of petroleum
hydrocarbon bioremediation by rhamnolipids was twice as efficient compared to
commercial chemical dispersants, GM-2, without any toxic effect on microorganisms. Moreover, when assessing the effect of surfactant combination, a consistent
negative effect of GM-2 on rhamnolipids’ efficiency was observed.
Because of the above-mentioned disadvantages of synthetic surfactants, especially higher toxicity, low selectivity, and higher CMC values, their effective
eco-friendly replacement with biosurfactants is sought. However, synthetic surfactants remain dominant because of the disadvantages of biosurfactants, particularly
their high price (Lau et al. 2014). Thus, the most feasible cost-effective alternative to
498
M. Halecký and E. Kozliak