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2
018; Manoel et al. 2015; Rios et al. 2018). It has been
shown that immobilization oꢀ lipases on hydrophobic sur-
aces (designated as interꢀacial activation) lets the ‘open’
orm oꢀ lipases to be more stable (Cantone et al. 2013; Hane-
eld et al. 2013; Sheldon and Pelt 2013).
This valuable biocatalyst has been widely employed in
alkaline lipase production (Bisht et al. 2012). The improved
strain was capable to secrete a high titer oꢀ alkaline lipase
(1609 U/l) into the medium (Bisht et al. 2012). Darvishi
et al. (2011) also applied the EMS to improve the productiv-
ity oꢀ lipase ꢀrom Yarrowia lipolytica.
ꢀ
ꢀ
ꢀ
Investigation on the ꢀactors inꢂuencing the production oꢀ
biomolecules is essential in many bioprocess development
procedures (Forootanꢀar et al. 2015; Moshaꢁ et al. 2011).
Generally, a higher productivity could be achieved by cul-
ture medium optimization (Haider Ali et al. 2015; Hasan-
Beikdashti et al. 2012; Riyadi et al. 2017). The statistical
optimization oꢀ processes has advantages compared to the
traditional method oꢀ varying one ꢀactor at a time (Colla
et al. 2016; Faisal et al. 2014) such as the lower number oꢀ
experiments and the possibility oꢀ evaluating the interaction
efects between ꢀactors. Statistical experimental techniques
such as two-level ꢀactorial experiments, Plackett–Burman
design (PBD), and response surꢀace methodology (RSM)
are efective tools applied ꢀor optimization oꢀ lipase pro-
duction by diferent microorganisms such as P. aeruginosa,
Candida rugosa, C. antarctica, B. cepacia, P. alcaligenes,
Rhizopus sp. and Bacillus pumillus (Liu and Zhang 2011;
Lo et al. 2012; Riyadi et al. 2017; Vasiee et al. 2016; Verma
et al. 2012).
ꢀ
ood industries (improving the quality oꢀ dairy products and
meat processing), detergent, pharmaceuticals, and cosmetic
industries, as well as in the synthesis oꢀ ꢁne chemicals, agro-
chemicals, biodiesel, and new polymeric materials (Darvishi
et al. 2011; Khoobi et al. 2014; Li et al. 2018). In pharma-
ceutical industries, lipases have been also used ꢀor kinetic
resolution oꢀ drug intermediates. Lipases have been applied
as co-catalysts in the preparation oꢀ enantiomer compounds
ꢀ
rom racemates (Pinheiro et al. 2018; Zhang et al. 2019;
Galvão et al. 2018).
Particularly, the speciꢁc lipases produce by extremophiles
have been used in harsh industrial conditions, because most
oꢀ them remain active at alkaline pH and in elevated tem-
perature as well as in the presence oꢀ high salt and organic
solvent concentrations (Samaei-Nouroozi et al. 2015; Yao
et al. 2013). There are many reports on bacterial derived
lipases categorized as extremophilic lipases. For example,
the secreted solvent-tolerant lipase oꢀ Burkholderia ambi-
faria YCJ01 was applied ꢀor resolution oꢀ (S)-mandelic acid
in the presence oꢀ diisopropyl ether (Yao et al. 2013). Yele
and Desai (2015) isolated a thermoalkalophilic lipase ꢀrom
Staphylococcus warneri which maximally worked at pH oꢀ
The present study was aimed to develop a B. atrophaeus
mutant strain with high ability ꢀor thermoalkalophilic lipase
production using chemically induced mutagenesis. Further-
more, the main ꢀactors afecting lipase biosynthesis by the
selected mutant were then screened and the related model
was evaluated. On the other hand, this research tried to
increase lipase production by a simple mutation method
combined with medium optimization using a statistical
experimental design (Scheme 1).
8
and temperature oꢀ 55 °C. Maximum esteriꢁcation oꢀ ethyl
butyrate assisted by lipase oꢀ Burkholderia multivorans V2
occurred at n-hexane (Dandavate et al. 2009).
In the last ꢀew decades, the ever-increasing usage oꢀ
lipases required the expansion in both qualitative improve-
ment and quantitative enhancement (Bisht et al. 2012;
Toscano et al. 2011). Quantitative enhancement could be
achieved by strain improvement and medium optimization
(
Toscano et al. 2011). Various methods have been used to
Materials and methods
improve the lipase producing strains including site-directed
mutagenesis and random mutagenesis (Bisht et al. 2012;
Chang and Shaw 2009; Iꢀtikhar et al. 2010). The classical
random mutagenesis approach mainly involves exposing the
desired microbe to the physical mutagens (such as X-rays,
gamma rays, and UV irradiation), or chemical mutagens
Chemicals and bacterial strain
Brain heart inꢀusion broth (BHIB), nutrient broth, tryp-
tone, yeast extract, sucrose, glucose, rhodamine B, and agar
were supplied by Merck Chemicals (Darmstadt, Germany).
ρ-Nitrophenylpalmitate (ρNPP), ρ-nitrophenol (ρNP), and
ethidium bromide (EtBr) were provided by Sigma-Aldrich
(St. Louis, MO, USA). All applied chemicals were oꢀ ana-
lytical grade. The lipase-producing bacterial strain (B.
atrophaeus FSHM2, NCBI accession number oꢀ KF682367)
employed in the present study was isolated in a previous
study ꢀrom a hypersaline location (30°36′18″N, 59°04′04″E)
in Kerman, Iran. The secreted lipase oꢀ this strain maximally
worked at 70 °C, pH 9, and in the presence oꢀ 4 M NaCl
(Ameri et al. 2017).
[
like N-methyl-N′-nitro-N-nitrosoguanidine (NTG), ethyl
methanesulꢀonate (EMS), and ethidium bromide (EtBr)].
Devi et al. (2015) used chemical mutagens oꢀ EMS, EtBr,
sodium azide, and NTG to enhance the production and lipo-
lytic potential oꢀ Pseudomonas sp. This mutant represented
a total increase in activity (4960 U/l) over its wild strain
(
3100 U/l) ꢀor the production oꢀ extracellular lipase (Devi
et al. 2015). In another study, the strain improvement oꢀ
P. aeruginosa MTCC 10055 was perꢀormed by chemical
mutagenesis using the mutagen 4-nitroquinoline 1-oxide ꢀor
1
3