Contribution of Fermentation Technology to Building Blocks for Renewable Plastics

Round 1

Reviewer 1 Report

The review ia attached.

Comments for author File: Comments.pdf

Author Response

Reviewer 1:
The paper “ Contribution of fermentation technology to building blocks for renewable plastics” describes subject related with Renewable plastics. This paper fits to Fermentation journal fields.
Paper is well written, the review was performed according , correctly however some of the Authors' explanations need clarificatio. I provided some recommendations that in my opinion would allow the Authors to improve the paper. English is generally correct, but I suggest Authors to make a correction.
Decision: accept after minor changes
Comments and Suggestions for Authors
49 – „less than 10% of plastic is recycled”- I suggest provide references.
Thank you for pointing out this error. The reference has been added as suggested.
125-131 – No text justification.
Revised as suggested.

 

Reviewer 2 Report

49 – „less than 10% of plastic is recycled”- I suggest provide references.

125-131 – No text justification.

 

The paper “ Contribution of fermentation technology to building blocks for renewable plastics” describes subject related with Renewable plastics. This paper fits to Fermentation journal fields.

Paper is well written, the review was performed according , correctly however some of the Authors' explanations need clarificatio. I provided some recommendations that in my opinion would allow the Authors to improve the paper. English is generally correct, but I suggest Authors to make a correction.

Decision: accept after minor changes

Author Response

Reviewer 2.

This manuscript describes in detail fermentation as a route for the production of bioplastics monomers. The writing is clear, and the technical knowledge is sound. However, a few queries need to be addressed before accepting for publication.

1. Check the reference formatting, the references do not match after references 50-6o. This is crucial, and do not make this kind of mistake while the writing is good.

Thanks to reviewer for pointing out this error. We revised references for the whole manuscript as suggested.

 

1. Include a separate and detailed future perspectives section, touching upon the recent gene-editing techniques and multi-omics approach.

Thanks to reviewer for the suggestion. The separate future perspectives section has been added to manuscript, Lines 760-791.

“4. Future perspectives

Triggered by the negative impact on the environment from large amounts of fossil-based plastic production and post-consumer plastic waste, research on renewable plastics has been increasing. More focus has been dedicated to the biodegradable ones, illustrated by more than 20% market growth compared to three years ago. By far, all types of renewable plastics have been shown the possibility to be synthesized from bio-based building blocks, at least on the laboratory scale. Fermentation technology plays an important role in developing bio-based building blocks for renewable plastics. Monomers for PBAT, PBS, PLA, drop-in, PTT, and PEF have been reported to obtain from fermentation by both natural and engineered strains. Some of these polymers even reached the commercialization stage, e.g., partially bio-based PBS synthesized from bio-based succinic acid from the fermentation of renewable feedstock or PTT synthesized from bio-based 1,3-PDO from engineered bacterial strains. PHA fermentation has also been developed using both renewable biomass and conventional plastic waste as feedstock. Next, efforts toward developing low-cost and high-titer processes are needed to accelerate commercialization.

Metabolic engineering is the key driver for the industrialization of renewable plastics by facilitating the bio-production of commodity chemical building blocks. Previously, E. coli was genetically manipulated to produce biochemicals such as D-lactate [193] and succinate [194]. These benefit the future up-scaled production as E. coli is a well-characterized species and has simple nutrient requirements. Omics technologies contribute to advancement in metabolic engineering. They help, for instance, unravel the metabolic pathway of unculturable microorganisms or provide the data of beneficial mutations during adaptive laboratory evolution. Multi-omics approaches with computational system biology, protein engineering, and synthetic biology are the tools for establishing new (or unconventional) metabolic pathways producing desired plastic monomers [196]. For example, a proteomics-guided approach has been used to engineer polyketide synthases for in vitro production of adipic acid [195]. Such technologies also broaden the application of microbes in bio-upcycling; for example, the unraveling of EG [197] and 1,4-BDO [198] metabolism in Pseudomonas putida KT2440 were succeeded by genome sequencing and proteomics analysis, which could be beneficial to upcycle plastic monomers. Using metabolic engineering tool-set is an interesting outlook that will facilitate discovering new bio-based building blocks production routes that help meet the market demand of renewable plastic.”

 

1. Improve the conclusions and give them as a separate section.

Thanks to reviewer for the suggestion. The separate conclusion section has been added to manuscript, Lines 792-825.

“5. Conclusion and future perspectives

The role of plastics in our society and economy is growing every year, but the rate of reuse and recycling is relatively low, showing considerable plastic pollution problems. Renewable plastics are materials of interest, for their potential contribution to alleviating negative environmental impacts seen with conventional fossil-based plastics, even though they are not going to solve the problem of poor waste management or low recycling rates, per se. Bio-based plastics promote carbon-neutral plastic production, using renewable biomass instead of depleting petrochemicals. The benefits would be magnified if they were designed to be biodegradable or compostable, allowing the carbon to re-enter the biogenic cycle, whenever reuse (think about facemasks) or closed-loop recycling (i.e. munch films) is not possible. Moreover, a recent study sug-gested that increased recycling rates would allow decreasing the cost of recycled bio-plastics by almost 50%, which is not the case with fossil-based ones (where recycled plastics are still more expensive than the virgin ones). The growth rate of global bio-plastics production is expected to be more than 200% within the next five years [22], so they will reach a larger market share and become more of general use.  The production of renewable and more bio-based plastic polymers, together with the development of new upcycling technologies, can thus provide a significant contribution to more sus-tainable plastic industry.

Currently, bio-based precursors of renewable plastic are forecasted to have a total growth of 4.5% by 2023 [199][181]. This will be achieved thanks to a significant contribution of fermentation technology that enables microbial production of various building blocks, such as 1,4-BDO, 1,3-PDO, FDCA, succinic acid, and other new fermentative compounds (azelaic acid, lactones, etc.). The advances in molecular biotechnology and bioprocess engineering have led to the development of superior microbial cell factories for unconventional bioproducts and more effective fermentation processes for increasing their titers. The good example would be the traditionally petroleum-based biodegradable PBS that currently able to be synthesized from bio-based succinic acid and 1,4-BDO produced by metabolic engineered bacteria. New emerging plastic building blocks obtain through fermentation are turning toward polymers that can be formulated to be recyclable materials, contributing to the solution of the end-of-life issue. Moreover, new bio-based building blocks should lead to polymers with superior functional properties. Future efforts are going to be dedicated to the scale-up of these technologies, to reach industrial scale and decrease production costs, which are still not competitive with conventional fossil-based plastics.”

 

1. Provide the structure of the monomers in Section 3.

The picture showing chemical structure of plastic building blocks have been added as “Figure 4” as suggested.

 

1. Abbreviate PFF at the first mention, here it is given later.

The abbreviation for poly(ethylene furanoate) was given as PEF at its first mentioned at Line 95.

Also, the abbreviation for polybutylene succinate that was previously not given at its first mentioned has been revised (added PBS as an abbreviate at its first mentioned at Line 139).

 

1. Line 472, please describe the "biotechnological breakthrough" - the actual fermentation conditions, substrate, microbe, and PBS yield.

Thanks to reviewer for the comment. The word of choice we used indeed leads to the misunderstanding of the point that we want to discuss. Therefore, we change the word, and additional discussion has been added to the manuscript, Lines 490-499.

 

“Traditionally, PBS monomers are produced from fossil-based feedstock [11], but recent biotechnological advancements allowed to produce both succinic acid and 1,4-BDO from renewable feedstock (sugar, starch, glycerol, lignocellulose, and other bio-waste), using non- or recombinant microbial strains [111]. In 2015, bio-based (50%) PBS production plant was opened in Thailand by a joint venture between PTT Public Company Limited and Mitsubishi Chemical Corporation, under the trade name ‘BioPBS™’. They used bio-based succinic acid from the fermentation of renewable feedstock such as sugarcane, cassava, and corn [112,113]. Fully bio-based PBS is expected to come shortly and could have at least 15–20% lower negative environmental impact than the fossil-based one [114].”

 

1. Introduce the recent reviews on the same topic in the introduction section, and justify the need for your review.

Thanks to reviewer for the suggestion. We have added the introduction to other relevance reviews in the introduction section of manuscript, Lines 98-105.

 

“Due to the complexity and diversity of the plastic value chain, scientific studies have tried to collect different information about topics, such as commercial applications, emerging renewable plastics, rational designs, material properties and characterizations, including definitions of bio-based and biodegradable plastics [2,8,16,17]. Some articles also summarize approaches and technology to produce green building blocks via chemical and biological routes [11,18–20]. However, it is imperative to have a comprehensive outlook on how biotechnological processes can contribute to the renewable plastic sector, while keeping a focus on the progress towards actual commercialization.”

 

1. The authors did not discuss the role of microalgae and cyanobacteria in bioplastics production. Please include this information.

Thanks to reviewer for the suggestion. We have pointed out the previous works on using microalgae/ cyanobacteria to produce PHA at Lines 444-449.

“In addition to bacterial strains, some microalgae and cyanobacteria also accumulate PHA granules in their cells. Despite the low PHA content, the advantage of using microalgae is that they can convert atmospheric CO₂ to PHA by autotrophic metabolism [104]. For example, Microcystis aeruginosa, Chlorella pyrenoidosa, Synechococcus subsalsus, and Spirulina sp. LEB-18 are reported species to produce PHB [105–107].”

Reviewer 3 Report

This manuscript describes in detail fermentation as a route for the production of bioplastics monomers. The writing is clear, and the technical knowledge is sound. However, a few queries need to be addressed before accepting for publication.

1. Check the reference formatting, the references do not match after references 50-6o. This is crucial, and do not make this kind of mistake while the writing is good.
2. Include a separate and detailed future perspectives section, touching upon the recent gene-editing techniques and multi-omics approach.
3. Improve the conclusions and give them as a separate section.
4. Provide the structure of the monomers in Section 3.
5. Abbreviate PFF at the first mention, here it is given later.
6. Line 472, please describe the "biotechnological breakthrough" - the actual fermentation conditions, substrate, microbe, and PBS yield.
7. Introduce the recent reviews on the same topic in the introduction section, and justify the need for your review.
8. The authors did not discuss the role of microalgae and cyanobacteria in bioplastics production. Please include this information.

Author Response

Reviewer 3:

Comments and Suggestions for Authors

1. Given that the graphs need to be visually clear, the authors should redraw these graphs (1; 2; 3; 4) as they are of poor quality.

The figures have been re-saved to high-resolution as suggested.

Reviewer 4 Report

Given that the graphs need to be visually clear, the authors should redraw these graphs (1; 2; 3; 4) as they are of poor quality.

Author Response

Reviewer 4:

Improve quality of figures.

The figures have been re-saved to high-resolution as suggested.