Current developments on polyhydroxyalkanoates synthesis by using halophiles as a promising cell factory

Abstract

Plastic pollution is a severe threat to our environment which necessitates implementation of bioplastics to realize sustainable development for a green world. Polyhydroxyalkanoates (PHA) represent one of the potential candidates for these bioplastics. However, a major challenge faced by PHA is the high production cost which limits its commercial application. Halophiles are considered to be a promising cell factory for PHA synthesis due to its several unique characteristics including high salinity requirement preventing microbial contamination, high intracellular osmotic pressure allowing easy cell lysis for PHA recovery, and capability to utilize wide spectrum of low-cost substrates. Optimization of fermentation parameters has made it plausible to achieve large-scale production at low cost by using halophiles. Further deeper insights into halophiles have revealed the existence of diversified and even novel PHA synthetic pathways within different halophilic species that greatly affects PHA type. Thus, precise metabolic engineering of halophiles with the help of advanced tools and strategies have led to more efficient microbial cell factory for PHA production. This review is an endeavour to summarize the various research achievements in these areas which will help the readers to understand the current developments as well as the future efforts in PHA research.

Production of the Polyhydroxyalkanoate PHBV from Ricotta Cheese Exhausted Whey by Haloferax mediterranei Fermentation

“…Indeed, it is reported that the major drawbacks faced by haloarchaea species, such as Hfx. mediterranei , are the low PHA productivity resulted from slow growth rate and failing to achieve high cell-density cultivation [ 37 ].…”

“…To maintain the optimal osmotic conditions for Hfx. mediterranei [ 37 ], the R-UF fraction was supplemented with NaCl. According to previous findings [ 37 ] the high salt concentration allowed to carry out the experiments in non-sterile conditions.…”

“…mediterranei [ 37 ], the R-UF fraction was supplemented with NaCl. According to previous findings [ 37 ] the high salt concentration allowed to carry out the experiments in non-sterile conditions. Nevertheless, contaminations of other non-halophilic microorganisms were excluded by regular microscopic observations.…”

“…Moreover, microbial cells can be easily lysed in normal water due to the high intracellular osmotic pressure; thus, further reducing PHA recovery cost [ 35 ]. However, the use of halophiles for large-scale PHA production is still associated to several issues [ 36 , 37 ]. Among these, the treatment of the saline fermentation effluent and the corrosion of the conventional fermentation equipment due to the high salt concentration of the substrates represent the main difficulties.…”

Bacterial Nanocellulose—A Biobased Polymer for Active and Intelligent Food Packaging Applications: Recent Advances and Developments

“…The main advantages of these materials include nontoxicity, biodegradability, plasticity, and selective gas permeability [ 43 , 44 ]. Meanwhile, the major drawbacks of microbial polymers that limit their competitiveness in commercial food packaging applications are both high production costs and relatively poor mechanical properties [ 44 , 45 ]. Currently, polyhydroxyalkanoates are mostly used as a packaging material for food with high oil content (e.g., olives, cheese, nuts), frozen, oxygen-sensitive, as well as organic products [ 18 , 46 , 47 , 48 ].…”