Role of Hydrodynamic Shear on Activity and Structure of Proteins
59
stirring at 500 rpm in the presence of air flow of 1 vvm also showed no
deactivation after a time period of 30 h. From these results it may be deduced
that the enzyme lipase is not affected by shear stress in conditions which exist
either during its production or further use in enzyme catalysed reactions.
Proteases are another class of industrially important enzymes which find
applications in different areas such as foods, detergents and the leather industry.
Proteases are commonly produced using aerobic microorganisms which secrete
the enzyme extracellularly. As stirred tank fermenters are most commonly used
for the production of these enzymes, a need to examine the effect of fluid forces
existing in these reactors on enzyme production and activity assumes significance. A study carried out by Gusek et al. [49] dealt with the production of
a serine protease by a filamentous aerobic bacterium Thermomonosporafusca.
The enzyme produced in conventional shake flask cultures as well in a stirred
tank reactor (baffled with two Rushton disk impellers of diameter 75 mm) under
agitated and aerated conditions was compared. The enzyme production in the
shake flask culture was on an average 16 times higher than that in the stirred
fermenter. Coating the impeller blades with tight fitting tygon tubing lead to
improved biomass and enzyme yields. Another feature of this study was that in
experiments conducted in shake flask and fermenter systems although the cell
biomass obtained was comparable in both the culture systems the protease
production in the shake flasks was significantly higher at 30 gg protease ml- ~ as
compared to 4.6 gg protease ml-1
The role of shear stress with respect to biosynthesis of enzymes, proteins and
even other metabolites such as antibiotics has been well documented. In most of
these cases hydrodynamic shear forces cause changes in the morphological
forms of the organism especially filamentous forms such as actinomycetes and
fungi [50]. As the production of metabolites is tightly coupled to the morphological form of the organism, the shear forces regulate metabolite formation
[51, 52]. Several reports describing these effects exist in the literature, however
since they primarily deal with the effect of shear on the microbes per se they are
not considered here. These effects have already been discussed in an earlier
review by the authors [41].
4.2 Cell Homogenization
Several microbial proteins are produced intracellularly. For their further application it is necessary to disrupt the cells and release product. There are several
methods used for disruption of cells which include mechanical, enzymatic and
chemical methods. Enzymatic treatment of cell disruption is mainly carried out
only on a laboratory scale as on an industrial scale the cost of the enzymes used
becomes prohibitive. Chemical methods of treatment are followed in certain
cases where mainly solvents and detergents are used for cell disruption. These
methods may be used when the cell walls have a greater content of lipopolysaccharides as in the case of Gram negative bacteria. However, when protein or
59
stirring at 500 rpm in the presence of air flow of 1 vvm also showed no
deactivation after a time period of 30 h. From these results it may be deduced
that the enzyme lipase is not affected by shear stress in conditions which exist
either during its production or further use in enzyme catalysed reactions.
Proteases are another class of industrially important enzymes which find
applications in different areas such as foods, detergents and the leather industry.
Proteases are commonly produced using aerobic microorganisms which secrete
the enzyme extracellularly. As stirred tank fermenters are most commonly used
for the production of these enzymes, a need to examine the effect of fluid forces
existing in these reactors on enzyme production and activity assumes significance. A study carried out by Gusek et al. [49] dealt with the production of
a serine protease by a filamentous aerobic bacterium Thermomonosporafusca.
The enzyme produced in conventional shake flask cultures as well in a stirred
tank reactor (baffled with two Rushton disk impellers of diameter 75 mm) under
agitated and aerated conditions was compared. The enzyme production in the
shake flask culture was on an average 16 times higher than that in the stirred
fermenter. Coating the impeller blades with tight fitting tygon tubing lead to
improved biomass and enzyme yields. Another feature of this study was that in
experiments conducted in shake flask and fermenter systems although the cell
biomass obtained was comparable in both the culture systems the protease
production in the shake flasks was significantly higher at 30 gg protease ml- ~ as
compared to 4.6 gg protease ml-1
The role of shear stress with respect to biosynthesis of enzymes, proteins and
even other metabolites such as antibiotics has been well documented. In most of
these cases hydrodynamic shear forces cause changes in the morphological
forms of the organism especially filamentous forms such as actinomycetes and
fungi [50]. As the production of metabolites is tightly coupled to the morphological form of the organism, the shear forces regulate metabolite formation
[51, 52]. Several reports describing these effects exist in the literature, however
since they primarily deal with the effect of shear on the microbes per se they are
not considered here. These effects have already been discussed in an earlier
review by the authors [41].
4.2 Cell Homogenization
Several microbial proteins are produced intracellularly. For their further application it is necessary to disrupt the cells and release product. There are several
methods used for disruption of cells which include mechanical, enzymatic and
chemical methods. Enzymatic treatment of cell disruption is mainly carried out
only on a laboratory scale as on an industrial scale the cost of the enzymes used
becomes prohibitive. Chemical methods of treatment are followed in certain
cases where mainly solvents and detergents are used for cell disruption. These
methods may be used when the cell walls have a greater content of lipopolysaccharides as in the case of Gram negative bacteria. However, when protein or