I spend a lot of time on this blog illustrating and promoting the benefits of the things we can’t see, however, we can’t live without and finding new ways they can help us out. To focus on bacteria along for now, they are beneficial overwhelmingly more than they are hazardous. Lots of research is going into utilizing them in new arenas from ethanol to diesel and jet fuels.
Helping solve the forthcoming energy/climate crisis is not the only area these guys can help. Lots of bacteria, under certain environmental conditions, can and will produce huge internal polymers as carbon stores, especially when nitrogen supplies are limited. Think of this polymer like starch in plants and glycogen in mammals. Research is still ongoing into the mechanisms that regulate polymer synthesis and degradation.
The bacterial polymer is special, unlike the molecular make-up of starch or glycogen, this polymer is a class of polyhydroxyalkanoate (PHA).
One of the most prevalent forms of PHA is polyhydroxybutyrate, or PHB. Speaking from experience, PHB is an interesting macromolecule to study and observe under the microscope with cells treated with a fluorescent dye that stains PHB. PHB can account for up to 75% of the total cell weight. PHB, and PHAs in general, can be used to make plastic thus replacing the need for petroleum based plastics.
Thanks to the decreasing costs of sequencing genomic DNA, finding novel microorganisms that add to our understanding of metabolism in myriad environments is becoming common place. Not only are we learning about the diversity of life in extreme environments, like heat, cold, pressure, and altitude, but we are also learning what life on other planets may be like. With each additional genome added into ‘the cloud’, our synthetic biology toolbox gets a little bit bigger and our ability to manipulate tiny organisms to produce novel compounds is possible. Enter the “rushing fireball”.
Pyrococcus furiosus is an archeal species that thrives near deep-sea thermal vents where temperatures are between 90 and 100 degrees Celsius (or 194 to 212 degrees F). P. furiosus can grow at temperatures as low as 70 degrees C (158 deg F). To live in such conditions, this organism’s proteins must be tolerant to what we would consider harsh conditions. This organism’s ambient conditions makes wild-type proteins well-suited for industrial processes where temperatures are near boiling.
So far, P. furiosus has been utilized to produce 3-hydroxypropionic acid, a common industrial chemical used to make various products including acrylics. The kicker is that these cells were wired to make this chemical from atmospheric carbon dioxide. It is not crazy to think of what other useful products can be produced by P. furiosus with small modifications within the genome; products like ethanol or butanol as biofuels.
I want to change focus a bit, from bacteria benefiting mankind by cleaning up our messes and providing electricity, to another great benefit of bacteria; their pliability. It is very easy to manipulate the genetics of bacteria (see Biohacking). This owes to their genome structure and lack of miles of “junk” DNA. This means scientists can insert genes from one bacterium into a more well-known bacterium, like E. coli, to perform a novel function and, in a way, reverse millions of years of evolution. For example, in 2011, Jay Keasling and his team at the Joint BioEnergy Institute (JBEI) modified E. coli to degrade switchgrass biomass into sugars. Not only that, the E. coli fermented the sugars into gasoline, diesel, or jet fuel without enzyme additives. Think about it; E. coli, a bacterium that colonizes the digestive tracts of mammals, is able to breakdown plant material and directly convert it into fuel. That is amazing. I’m working on an illustration to depict this, so check back.
Energy. We all have it and we all need it on multiple levels. Within our body, energy is stored in a molecular currency that is conserved among all living organisms, adenosine triphosphate, ATP. Of course, you should know that as humans, we require oxygen to live. During our metabolism, hydrogen atoms are divided into their two opposite parts, the proton and electron. The electrons are shuttled through several enzyme complexes while the protons are pumped out of the mitochondrial matrix creating a much greater proton concentration outside than inside. This imbalance is what drives Nature’s smallest rotary motor, ATP synthase. But what about the electrons? Your body has no need for them, energetically speaking so something needs to accept them for the big show to continue. In our case, the acceptor is oxygen. Oxygen accepts the electrons, and the protons that come along to reconstitute the full hydrogen atom, to form water, H2O. A lot of organisms need oxygen for the same reason. However, just as many organisms have no such requirement while some others are afraid of oxygen.
This leads to the question of what accepts the electrons within organisms that don’t have oxygen present? Anaerobic (“no oxygen”) respiration can utilize many different molecules to accept electrons depending upon the genetic capacity of the organism in question. The more genes within a genome that encode enzymes that can coerce compounds to accept electrons, the more options an organism has in regards of what environment they can survive and thrive. If you have kept up with this blog, you know about a group of bacteria that have evolved a variety of strategies to survive in some of the most undesirable environments on (or in) Earth; Geobacter.
Geobacter have been identified in many anaerobic environments including, soil, sediments, wetlands, and even rice paddies. Geobacter are the predominant species in these environments where there is no oxygen and few other choices for electron acceptors. They are very efficient with their energy usage as well as creative in the ways in which they “relieve” themselves of unwanted electrons. In the absence of oxygen, Geobacter have two major methods of removing the reducing power of electrons. The method of choice used depends upon the type of compounds within their environment capable of accepting electrons; soluble or insoluble. Soluble, water dissolving, compounds include many common organic materials such as amino acids and carbohydrates. Uptake of these molecules is possible and necessary. However, not all soluble compounds are easily tolerated by Geobacter including heavy metals. How can Geobacter utilize these electron acceptors if they can’t bring them inside their cell membranes? The answer is by taking the electrons outside the cell through a labyrinth of electron shuttling proteins called cytochromes. Cytochromes, especially the predominant Geobacter type cytochrome c, use prosthetic cofactors like hemes or copper ions to ferry electrons out of the cell to waiting acceptors.
This is where it gets interesting…
What if only insoluble electron acceptors are present? There’s an op for that! Operon that is. Actually, several operons that are active when sources of soluble electron acceptors are very low. Geobacter can synthesize extracellular appendages that can navigate over several cell lengths to find insoluble acceptor compounds including the predominant iron Fe3+ within the subsurface. These appendages called pili are found in many other bacteria. However, there is something a little more special about Geopili, they can conduct electricity. The protein subunits that compose the geopilus have a shorter peptide sequence than the one found in a majority of other pili systems. Also, a few of the cytochromes c proteins that shuttle electrons to the outer membrane of the cell can actual be deposited along the pilus to deliver electrons to waiting acceptors far away from the actual cell itself.