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Table 1 Advantages and disadvantages of homologous and heterologous protein expression in different host organisms in regard to technical, ethical and economic aspects

From: Challenges and advances in the heterologous expression of cellulolytic enzymes: a review

Organism Example Protein expression Advantages Disadvantages Expression challenges
Homologous cellulase production systems   
Fungi Trichoderma reesei 14 000 to 19 000 mg/l crude enzyme solution [79] Native system Enzyme mix cannot be tailored for different biomass substrates Special culturing conditions required
Protein secretor Comparably high production costs
High protein yield
Bacteria Bacillus subtilis (gram positive)   Inducible and auto-inducible expression possible Rich growth medium required as a carbon source, leading to increased costs Inducible systems more efficient but significantly more expensive
Easy to modify genetically
Protein secretor
  Clostridium thermocellum (gram positive)   Native system Low protein yield Special culturing conditions required
Cellulosome producing High production costs
Transient and stable transformation Unwanted byproducts
Heterologous cellulase production systems   
Bacteria Escherichia coli (gram negative) 11.2 to 90 mg/l purified enzyme solution [79] Industrially used, common system Thick outer membrane restricts protein secretion (poor secretion) Degradation of linker sequences in multi-domain cellulases
Well-characterized genetics Formation of inclusion bodies
Many commercially available strains and vectors Frequently incorrect transportation across the outer membrane
Easily to modify for example for protein engineering   Decreased specific activity of the cellulase can occur
Yeast Saccharomyces cerevisiae Approximately 1 000 mg/l crude enzyme solution [79] Protein secretor Hyperglycosylation Inducible systems are highly efficient but can be expensive
Surface display possible Expression rates lower than native systems Increased episomal gene copy numbers leads to higher protein yields but a constant selection is necessary
Industrially used, common system
Plants Nicotiana tabacum Up to 40% of total soluble protein, depending on the subcellular targeting inside the plant cell [79] Cheap protein production Transport of genetic information via pollen (if not transplastomic) Possible glycosylation effects
Easy transformation Long transformation procedure Subcellular targeting inside the plant cell very important for expression efficiency
Well-characterized genetics   Possible effects on plant growth behaviour
Protein and biomass
Production in one system
Non-food
  Zea mays Approximately 0.45% of dry weight [159] Cheap protein production Transport of genetic information via pollen (if not transplastomic) Possible glycosylation effects
Simultaneous biomass and enzyme production Long transformation procedure Subcellular targeting inside the plant cell very important for expression efficiency
System already used for biofuel production Food