User:Kinayaan

Topic: Production of Fusal Alcohol from Bacteria

Abstract

Real world application of fuel production from microbial sources has proven to be difficult in recent years, for many reasons. Biomass is converted into a usable fuel in various organisms, limited to plants and animals. Recently, interest has spiked to introduce these synthetic bio fuel pathways on an industrial scale, but many challenges are faced. Storing bio fuels can be extremely difficult; in addition, scaling these production processes is another prevalent barrier for introduction in industry. Achieving efficient fuel production from microorganisms is still a developing process, many methods today are being researched and analyzed that show potential implementation in industry.

Introduction

Bio fuels are a usable industrial fuel that are originally created from organic compounds, and molecularly they are primarily composed of hydrocarbons ^[6]. It has been known for decades that microbial organisms have the capability to make bio fuel, therefore introducing these fuel synthesis methods to an industrial scale has been a profound area for research and development over recent years [2].  Some examples of bio fuel include bio alcohols (ethanol, propanol, butanol), bio diesel, green diesel, vegetable oil/fat, bio gas, and various solid bio fuels [5]. The fuels are categorized into two major groups: 1^st and 2^nd generation bio fuels ^[6].. What separates the categories is the source of fuel, not the physical composition of fuel.  1^st generation fuels are directly made from a food crop, while 2^nd generation fuels require more advanced extraction techniques, and do not generally derive directly from a food crop source. 1^st generation fuels face many limitations: producing too much fuel from food crop cuts into food stock and could possibly damage usable farmland [2]. In result, 2^nd generation bio fuels are much more sustainable and hence the focus has been more concentrated on scaling 2^nd generation biofuel synthesis methods versus 1^st generation methods.  

Biofuels are desired for distinct reasons, all of which indicate that the overall sustainability compared to petroleum-based fuels holds a more promising future for humanity. Many metabolomic engineers today are focusing research on discovering or improving 2^nd generation (and further generation) biofuel synthesis methods.

Method I: Solar-To-Fuel Production

Solar power can be utilized to make biofuel through water splitting and yields hydrogen and oxygen _[1]. Hydrogen is difficult to store on its own, so it is often bridged with carbon dioxide to make hydrocarbon fuels that have storage capability ^Reference. Since hydrogen storage holds many challenges, the technique is to fix CO₂ directly into biomass and liquid biofuel via photovoltaic cell (PV). Traditionally, converting CO₂ into liquid hydrocarbon fuel has seen terrible energy efficiency; plants only achieve 1% of the thermodynamic maximum ^Reference. Torella, Gagliardi, Chen, Bediako, Colón, Way, Silver, Nocera did a study on using water splitting catalysts and a strain of metabolically engineered bacteria, Rastolnia Eutropha, along with a PV to produce biomass and isopropyl alcohol, resulting in the highest bio electrochemical fuel yield reported yet ^_[1].

Biofuel production requires many different reactions, some of which that utilize oxygen in key reactions called oxygen-evolution-reactions (OER’s). Many PV systems require an anaerobic bacterium, which can severely hinder the reaction rate for OER’s at the required reaction conditions; one method to overcome this hindrance is to introduce a metal catalyst to drive the reaction forward _^[1]. Even with introducing the metal catalysts, energy efficiency still is not maximized. The required cell potential to drive OER’s forward is substantially higher than the cell potential required for biological growth: 4.0 V-5.0 V compared to the required 1.23 V for biological growth _^[1]. In the study conducted by Torella and Gagliardi, the researchers overcome these barriers by incorporating a cobalt phosphate catalyst (CoP_i)_^[1]. The CoP_i catalyst can perform OER’s at low cell potentials because it shares many of the same qualities as the OER catalyst seen in photosystem II in plant organisms: it has similar structure, can self-repair, and can perform the necessary electron transfers required in water splitting.

The bioreactor system is designed so that water is split at the CoP_i anode end of the PV, and then the electrons are transferred to the protons via a Nickel Molybdenum Zinc (NiMoZn) cathode ^_[1]. Carbon dioxide is pumped into the cell during this entire process and the resulting reduced hydrogen is then oxidized by the bacterium Rastolnia Eutropha H16. Adenosine Triphosphate (ATP) and Nicotinamide adenine dinucleotide phosphate (NADPH) are produced and utilized as reducing equivalents which fix carbon via the Calvin Cycle to produce 3-phosphoglycerate (3PG). 3PG is used to produce biomass/bio-fuel, which can further react to create the fuel isopropanol ^_[1].

Method II: Fungal-Bacteria Consortia

Microbial consortia often demonstrate phenomenal metabolic characteristics in nature which has sparked some interest in developing useful methods for biofuel production [3]. A sagacious barrier encountered while industrially scaling these methods is due to stability of the consortia as the population increases. The food and farm industry provide an abundance of lignin, which is a common source for the synthesis of biofuel. To convert lignocellulose into a usable biofuel, many biological interactions need take place. An organism, or multiple, are needed to produce the cellulase enzymes, hydrolyze lignocellulose into saccharides, and then metabolize the saccharides into biofuel ^Reference. Minty, Singer, Scholz, Bae, Ahn, Foster, Liao, and Lin assembled a microbial consortium consisting of Trichoderma reesei (T. reesei) and Escherichia Coli (E. Coli) ^[3]. T. reesei secretes enzymes to break down lignocellulose into saccharides that are then metabolized by E. Coli into the desired biofuel, which is usually isobutanol ^[3].

To render the process more efficient, the goal was to design a method to combine the three separate steps of producing cellulase enzymes, hydrolyzing them, and subsequently metabolizing them, into one step via genetic engineering ^[3]. The engineering strategies also have many barriers before they can be utilized efficiently. Synthetic consortia are often very fragile, so when they are introduced to diverse communities of microbes they often dominate the population, which prevents necessary metabolic functions to occur within the population that result in a hindered ability to scale the consortia industrially ^[3]. One of the key challenges in the synthesized T.reesei/E.Coli consortia is that the fungus and bacteria are competing for hydrolyzing the saccharides produced from lignocellulose, which indicates the relationship between hydrolysis rate and biofuel yield [3].

The consortia can be improved by applying ecology theory to predict the stability and interactions within the population. For example, for the T.reesei/E.Coli consortia, the two organisms follow cooperator and cheater dynamics ^[3]. T. reesei cooperates by expending energy to hydrolyze saccharides and E. Coli cheats by metabolizing the saccharides at no energy cost ^[3]. Understanding these dynamics can give insight on how to improve reaction rates and therefor biofuel yield.

1.     Torella, Joseph P.; Gagliardi, Christopher J.; Chen, Janice S.; Bediako, D. Kwabena; Colón, Brendan; Way, Jeffery C.; Silver, Pamela A.; Nocera, Daniel G. (2015-02-24). "Efficient solar-to-fuels production from a hybrid microbial–water-splitting catalyst system". Proceedings of the National Academy of Sciences. 112 (8): 2337–2342. doi:10.1073/pnas.1424872112. ISSN 0027-8424. PMID 25675518

2.     "Partial Correlation in SPSS Statistics - Procedure, assumptions, and output using a relevant example". statistics.laerd.com. Retrieved 2018-03-13.

3.     Minty, Jeremy J.; Singer, Marc E.; Scholz, Scott A.; Bae, Chang-Hoon; Ahn, Jung-Ho; Foster, Clifton E.; Liao, James C.; Lin, Xiaoxia Nina (2013-09-03). "Design and characterization of synthetic fungal-bacterial consortia for direct production of isobutanol from cellulosic biomass". Proceedings of the National Academy of Sciences. 110 (36): 14592–14597. doi:10.1073/pnas.1218447110. ISSN 0027-8424. PMID 23959872

"Extracellular electron transfer from cathode to microbes: application for biofuel production"doi10.1186/s13068-016-0426-0ISSN1754-6834PMC4717640 PMID26788124

5.     "Biofuels - Types of Biofuels". biofuel.org.uk. Retrieved 2018-04-24.

6.     http://www.igem.org.uk/media/405523/biofuels%20final%20report.pdf

Ajayi-Oyakhire, Olu; Mohammed, Mohsin (2016). “Biofuels: Analysis of the Various Biofuel Types Including Biomass, Bioliquids, Biogas, and Bio-SNG”. Institution of Gas Engineers and Managers