PHAs limit their competitive forces to substitute traditional synthetic plastics.
Modification of PHAs to achieve better performance has attracted increasing attention from industry and scientific research organizations and has gained excellent
achievements in materials and medical applications [19]. In spite of formal and
temporary obstacles, PHAs with various compositions of esters have established
their position in the bioplastic market. The present production of bioplastics is made
with genetically engineered microbes grown in neutral conditions. Haloalkaliphilic
microbes can accumulate >50% of their dry weight with PHA-related compounds.
The alkaline microbial producers have been reviewed by Zhao et al. [18]. Recently, a
wide systematic approach was described to improve PHA biosynthesis by engineering microorganisms [20]. Plastics have got so prevalent position in human life that it
is unlikely that it can be easily substituted. The biodegradable plastics shall find their
specific place in the consumer use. Bioplastics can be based also on composite
materials from different sources, like microbial and plant polymers. Considerable
technological efforts exist in this field, for example, in composites of cellulose and
polylactic acid (https://makingoftomorrow.com/biocomposites-insights-patent-land
scape). The composites allow using of cheaper raw materials together with the
binder plastics. It is illustrating that the total number of patents on bio-composites
is about 14,400 after the year 2000 (see the above presentation).
4 Compatible Solutes (CSs)
Microorganisms living in extreme environments must often adapt to fast changes
in physical (heat, cold, radiation, compression, shearing) and chemical conditions
(ionic strength, oxygen, pH) to maintain cellular functions like turgor pressure, cell
volume, and ionic strength in tolerable limits. Genetic studies show that alkaliphiles
do have many arrangements for that in different levels of the cell physiology
[21]. That is, microbes can react to several simultaneous stress factors. One part of
that is considered to be achieved by regulation of small molecular compound called
osmolytes or osmoprotectants. They are inert molecules not affecting the overall
cellular functions, although they can modulate individual events like protein folding,
enzyme activities, and a multitude of bioaffinity events. Because these compounds
may have also other functions than regulation of osmotic pressure, the term compatible solute (CS) has been adapted. This is more exact term than osmolyte when
the function is not known. Molecular structures of CSs can be anionic, cationic, or
neutral, and their molecular sizes can be different. The structures and functions of
CSs related to halophilic microbes are reviewed by Roberts [22]. In a way, CSs could
act as “molecular relaxants” when bound to a protein, for example, they could
maintain flexible structure of the protein by the ability of CSs to have various
tautomeric or resonance structures (e.g., ectoines). The cited review also shows
extensive list of CSs and discusses their biosynthesis. Although the review focuses
to halophiles, the major part of it is also relevant to alkaliphiles. Zhao et al. [18] have
reviewed the most known CSs from haloalkaliphiles including ectoines and betaines.
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
167
Modification of PHAs to achieve better performance has attracted increasing attention from industry and scientific research organizations and has gained excellent
achievements in materials and medical applications [19]. In spite of formal and
temporary obstacles, PHAs with various compositions of esters have established
their position in the bioplastic market. The present production of bioplastics is made
with genetically engineered microbes grown in neutral conditions. Haloalkaliphilic
microbes can accumulate >50% of their dry weight with PHA-related compounds.
The alkaline microbial producers have been reviewed by Zhao et al. [18]. Recently, a
wide systematic approach was described to improve PHA biosynthesis by engineering microorganisms [20]. Plastics have got so prevalent position in human life that it
is unlikely that it can be easily substituted. The biodegradable plastics shall find their
specific place in the consumer use. Bioplastics can be based also on composite
materials from different sources, like microbial and plant polymers. Considerable
technological efforts exist in this field, for example, in composites of cellulose and
polylactic acid (https://makingoftomorrow.com/biocomposites-insights-patent-land
scape). The composites allow using of cheaper raw materials together with the
binder plastics. It is illustrating that the total number of patents on bio-composites
is about 14,400 after the year 2000 (see the above presentation).
4 Compatible Solutes (CSs)
Microorganisms living in extreme environments must often adapt to fast changes
in physical (heat, cold, radiation, compression, shearing) and chemical conditions
(ionic strength, oxygen, pH) to maintain cellular functions like turgor pressure, cell
volume, and ionic strength in tolerable limits. Genetic studies show that alkaliphiles
do have many arrangements for that in different levels of the cell physiology
[21]. That is, microbes can react to several simultaneous stress factors. One part of
that is considered to be achieved by regulation of small molecular compound called
osmolytes or osmoprotectants. They are inert molecules not affecting the overall
cellular functions, although they can modulate individual events like protein folding,
enzyme activities, and a multitude of bioaffinity events. Because these compounds
may have also other functions than regulation of osmotic pressure, the term compatible solute (CS) has been adapted. This is more exact term than osmolyte when
the function is not known. Molecular structures of CSs can be anionic, cationic, or
neutral, and their molecular sizes can be different. The structures and functions of
CSs related to halophilic microbes are reviewed by Roberts [22]. In a way, CSs could
act as “molecular relaxants” when bound to a protein, for example, they could
maintain flexible structure of the protein by the ability of CSs to have various
tautomeric or resonance structures (e.g., ectoines). The cited review also shows
extensive list of CSs and discusses their biosynthesis. Although the review focuses
to halophiles, the major part of it is also relevant to alkaliphiles. Zhao et al. [18] have
reviewed the most known CSs from haloalkaliphiles including ectoines and betaines.
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
167