By: Sarah Afzaal '19 and Kyra Seiger '19
In any conversation concerning the environmental issues facing our world, it’s almost impossible not to mention the damage caused by fossil fuels. We use them everyday to run our cars and generate the electricity that powers our homes. In fact, about 63.5% of electricity in the US is produced through fossil fuels. However, these widely used, yet limited, energy sources have taken a toll on the environment by causing air pollution and global warming, both of which are growing concerns.
As a result, more environmentally friendly sources of energy are being considered and put into use. Biofuels, for example, are energy sources derived from plants that have been broken down. The production processes tend not to have harmful byproducts or consequences. However, it has proven difficult to mass produce these biofuels. Processing the plants themselves requires a great amount of energy, often close to the amount of biofuel that is actually produced. Current research is looking for ways to reduce this energy input. One possible and promising production process employs an unusual, yet creative, method: bacteria.
Paenibacillus vortex is one bacterium with the power to, well, create power. Before getting into its potential application in biofuel production, some background on the other unique aspects of P. vortex is needed. P. vortex is a notorious swarmer in the microbial world. Swarming, a social activity, occurs when bacteria gather together on a surface and move across it using their flagella. This collective movement reduces surface tension and allows the group to move more efficiently than a single bacterium could do alone. Plenty of bacteria, such as Escherichia coli and Serratia marcescens swarm, but P. vortex swarming is as close as you can get to bacterial mosh-pitting.
Coswarming, when different species of swarming bacteria swarm together, is common. However, P. vortex is a rare example of a bacterium that will carry non-motile bacteria and even fungi along for the ride. P. vortex will lend a hand to the spores of the fungus Aspergillus fumigatus across long distances (tens of centimeters!) in a mutually beneficial relationship. The spores wouldn’t be able to move without P. vortex, but they are able to germinate and provide a bridge for P. vortex to cross gaps in the soil that the bacteria would not otherwise be able to traverse. For more information about this phenomenon, look here. P. vortex can also be picky with what bacteria it chooses to cargo. For example, P. vortex will only carry a non-motile E. coli strain while swarming if the cargo benefits P. vortex: the E. coli has to be antibiotic resistant when P. vortex finds itself in a toxic environment. Antibiotic resistance in bacteria, particularly in pathogenic bacteria, is a widespread and major health concern. P. vortex’s propensity to carry antibiotic-resistant bacteria far distances may be contributing the spread of resistance throughout bacterial communities. For more information about this, look here.
In any conversation concerning the environmental issues facing our world, it’s almost impossible not to mention the damage caused by fossil fuels. We use them everyday to run our cars and generate the electricity that powers our homes. In fact, about 63.5% of electricity in the US is produced through fossil fuels. However, these widely used, yet limited, energy sources have taken a toll on the environment by causing air pollution and global warming, both of which are growing concerns.
As a result, more environmentally friendly sources of energy are being considered and put into use. Biofuels, for example, are energy sources derived from plants that have been broken down. The production processes tend not to have harmful byproducts or consequences. However, it has proven difficult to mass produce these biofuels. Processing the plants themselves requires a great amount of energy, often close to the amount of biofuel that is actually produced. Current research is looking for ways to reduce this energy input. One possible and promising production process employs an unusual, yet creative, method: bacteria.
Paenibacillus vortex is one bacterium with the power to, well, create power. Before getting into its potential application in biofuel production, some background on the other unique aspects of P. vortex is needed. P. vortex is a notorious swarmer in the microbial world. Swarming, a social activity, occurs when bacteria gather together on a surface and move across it using their flagella. This collective movement reduces surface tension and allows the group to move more efficiently than a single bacterium could do alone. Plenty of bacteria, such as Escherichia coli and Serratia marcescens swarm, but P. vortex swarming is as close as you can get to bacterial mosh-pitting.
Coswarming, when different species of swarming bacteria swarm together, is common. However, P. vortex is a rare example of a bacterium that will carry non-motile bacteria and even fungi along for the ride. P. vortex will lend a hand to the spores of the fungus Aspergillus fumigatus across long distances (tens of centimeters!) in a mutually beneficial relationship. The spores wouldn’t be able to move without P. vortex, but they are able to germinate and provide a bridge for P. vortex to cross gaps in the soil that the bacteria would not otherwise be able to traverse. For more information about this phenomenon, look here. P. vortex can also be picky with what bacteria it chooses to cargo. For example, P. vortex will only carry a non-motile E. coli strain while swarming if the cargo benefits P. vortex: the E. coli has to be antibiotic resistant when P. vortex finds itself in a toxic environment. Antibiotic resistance in bacteria, particularly in pathogenic bacteria, is a widespread and major health concern. P. vortex’s propensity to carry antibiotic-resistant bacteria far distances may be contributing the spread of resistance throughout bacterial communities. For more information about this, look here.
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| When P. vortex (stained red) is plated with antibiotic resistant E. coli (stained green) on an agar plate containing antibiotic, P. vortex will carry E. coli along to degrade the antibiotic as it swarms. The authors called this “mutualism of convenience.” |
In a recent study, a group of researchers at Tel Aviv University, Mark Polikovsky, Eshel Ben-Jacob, and Alin Finkelshtein, found that P. vortex’s swarming ability and cargo strategy may make it an effective biofuel producer. A typical plant cell wall is composed primarily of two polysaccharides: cellulose and xylan. In order to produce biofuel from plants, these complex cell wall sugars must be degraded into simpler sugars, which are then converted into usable fuels, such as ethanol.
The primary method of degrading the complex sugars of the cell wall for biofuel production is the application of high heat and chemicals. Not only is the process complex, but it requires major energy consumption to generate the heat (300°C to 1,000°!), not to mention the machinery of biofuel refineries. P. vortex, on the other hand, is able to degrade xylan as a nutrient source naturally. Instead of humans consuming energy to degrade the cell wall, P. vortex actually acquires its energy through the breakdown of xylan. In addition, P. vortex can spread on its own to new sites to degrade even more xylan once it uses up all the xylan in an area. As a visual reflection of this, P. vortex is able to travel 30 mm when it has access to xylan, but only 11-12 mm if xylan is absent, as seen below.
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| When plated with either i. just media, ii. media and peptone, or iii. media and xylan, P. vortex (shown in yellow) swarms significantly further when it is able to degrade xylan for its nutrient source. |
Unfortunately, xylan makes up a small percentage of most plant cell walls. Thus degradation of xylan alone would not generate significant amounts of biofuel. Cellulose is the major source of plant fiber and the major source of sugars for biofuel production. Specifically, cellulose can be converted into ethanol. Because P. vortex can only degrade xylan, it may seem like its potential use in biofuel production is limited. However, as mentioned earlier, P. vortex will carry other bacteria if they can provide a benefit to it. If for some reason, there is a limited supply of xylan for P. vortex to consume, it will pick up and carry bacteria that can degrade the other sugars that are available.
In this study, the alternative sugar source was cellulose. The researchers hypothesized that if P. vortex does not have access to xylan, it will willingly carry bacteria that can degrade cellulose. When the other bacteria break down the cellulose into more simple sugars, P. vortex would be able to take in these sugars as nutrients. Since E. coli has previously been known to cooperate with P. vortex, E. coli that was genetically modified to produce compounds needed for cellulose degradation was chosen to be the “cargo” bacterium. When cellulose is the only carbon source present, this bacterial pairing will mutually benefit both parties: the cellulose-degrading E. coli has free transportation and therefore is able to access and break down more cellulose, while P. vortex now has access to the nutrients from the degraded cellulose.
To observe the collaboration and mutual benefits of this bacterial pairing, researchers tested controls of each bacteria growing alone and compared them to when they were growing in consortium with each other. P. vortex alone, E. coli alone, and P. vortex with E. coli were each plated at the center of agar plates that had soluble cellulose as the only carbon source. The bacteria were left to grow for 14 days, and stained blue for easier visualization of the bacterial growths. The distances travelled by the bacteria from the center of the plate was measured as the means of understanding its “success”: proliferation at larger distances meant the bacteria prospered more.
The leftmost image of the figure above shows the results of when wild-type E. coli and genetically modified E. coli were grown together on an agar plate. The colony diameter was only 5.4 mm. The genetically modified E. coli, despite being able to degrade cellulose, cannot spread on its own to degrade more cellulose nearby. It was only able to multiply locally and take in nutrients produced through its degradation of cellulose where it was first plated.
The center image paired, in equal amounts, P. vortex with wild-type E. coli that cannot break down cellulose. P. vortex did not carry and spread the E. coli since this wild-type E. coli did not degrade cellulose and therefore did not do anything to benefit P. vortex. P. vortex itself was also unable swarm much because there were no nutrients present for it to take in since no cellulose had been degraded. As a result, its growth and swarming was very limited: the overall colony diameter was 10.75 mm.
The rightmost image shows widespread growth of both P. vortex and genetically modified E. coli, which were present in equal amounts. The successful spread of the consortium of bacteria indicated that P. vortex had obtained enough nutrients, which were produced by the E. coli when it degraded cellulose, to travel and carry the beneficial E. coli along with it. The pairing multiplied and spread, having a large colony diameter of 78.4 mm. This was a drastic change from the previous agar plates. This final experiment showed the extent to which both species of bacteria prospered in this relationship.
This experiment is important in showing that a consortium of P. vortex and E. coli is effective in degrading complex plant cellulose and could thus be used in biofuel production. The pairing benefits both organisms when in an environment where cellulose is the only carbon source, so no other measure seems to be needed to make them work together. This fact is beneficial for us humans because it would require less energy and resource input to produce ethanol. Biofuel production is very costly and inefficient in terms of both energy input required and quantity of biofuel produced. This bacterial collaboration between notorious swarmer P. vortex and the cellulose-degrading E. coli has the potential to degrade high amounts of cellulose and thus allow for mass production of ethanol. If biofuel could be mass produced by bacteria, it could rival the more widely available fossil fuels since the aftermath of both the production and use of biofuels is much cleaner and more environmentally friendly.
The pairing is better than P. vortex alone because it allows for the main plant fiber cellulose, not just xylan, to be broken down into ethanol. As a result, larger quantities of ethanol would be produced. However, this study did not determine how P. vortex and genetically modified E. coli would interact if both cellulose and xylan were present as carbon sources. It is unclear if P. vortex would even need to degrade xylan if cellulose was already being broken down as an available nutrient source by E. coli. If P. vortex and the genetically modified E. coli could degrade both major plant fibers at the same time, biofuel production would be even more efficient. It would be a two-in-one process!
This paper shows promising data that collaboration between P. vortex and cellulose-degrading bacteria may be used to degrade plant biomass. However, there are many exciting questions left unanswered. For example, what other bacteria can P. vortex transport that have the innate ability to degrade cellulose as opposed to the E. coli that was engineered to degrade cellulose? Is there a limit to how far P. vortex can travel from its starting point? This would affect how much cellulose could be degraded at once from a cargo bacteria. If we can answer these questions, then who knows, P. vortex may just be the answer to the global call for natural fuel sources.
The pairing is better than P. vortex alone because it allows for the main plant fiber cellulose, not just xylan, to be broken down into ethanol. As a result, larger quantities of ethanol would be produced. However, this study did not determine how P. vortex and genetically modified E. coli would interact if both cellulose and xylan were present as carbon sources. It is unclear if P. vortex would even need to degrade xylan if cellulose was already being broken down as an available nutrient source by E. coli. If P. vortex and the genetically modified E. coli could degrade both major plant fibers at the same time, biofuel production would be even more efficient. It would be a two-in-one process!
This paper shows promising data that collaboration between P. vortex and cellulose-degrading bacteria may be used to degrade plant biomass. However, there are many exciting questions left unanswered. For example, what other bacteria can P. vortex transport that have the innate ability to degrade cellulose as opposed to the E. coli that was engineered to degrade cellulose? Is there a limit to how far P. vortex can travel from its starting point? This would affect how much cellulose could be degraded at once from a cargo bacteria. If we can answer these questions, then who knows, P. vortex may just be the answer to the global call for natural fuel sources.
About the Authors:
Kyra Seiger '19 is a graduating Biology major and works in the Lijek Lab at Mount Holyoke College. She is going on to study the scope and maintenance of latent HIV reservoirs at the Ragon Institute of MGH, MIT, and Harvard before going to medical school. She enjoys a nice Pinot Grigio on the beaches of Block Island, RI, and would never say no to chocolate.
Sarah Afzaal '19 is a biology major with a minor in chemistry from Albany, NY. She enjoys reading, playing board games, and watching horror movies during her free time. After graduation, she hopes to attend medical school and pursue a career as a physician.
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