On Tonight’s Episode: “Fatty” Microbes!

By HJ

Interviewer: (To the audience) Maybe you’ve heard before that water makes up about 98% of the total molecules in the human body. You might be skeptical; we aren’t splashing around on the floor after all. OK, the number may seem a bit misleading since water molecules are a lot smaller than the other molecules being compared, such as proteins. But still, even if we go by the weight of the molecules, water dominates at about 65% (1). What if I told you that some organisms dedicate that much of its weight for fats? No, I’m not talking about obesity. I’m talking about microscopic organisms that can mass-produce fats when the right time comes. Here with me today are Lipomyces starkeyi, Yarrowia lipolytica, and Chlorella vulgaris. (To the microbes) Thanks for joining me, guys!

Microbes: (Smiling) Glad to be here.

Interviewer: So how are we doing? Enjoying the nice weather?

Lipomyces starkeyi (Starkey): You’re kidding me, right?

Lipomyces starkeyi   

Yarrowia lipolytica (Rowie): Starkey’s right. We’ve got so many neighbors around eating our food.

Yarrowia lipolytica   

Chlorella vulgaris (Ella): I mean, can’t you see how fat we are?

Chlorella vulgaris   

Interviewer: So you’re saying that being hungry makes you fat?

Starkey: In a way, yes. We start storing carbons once we run out of nitrogen (2–4). As you may or may not know, nitrogen is essential—

Ella: Because we need nitrogen in our DNA and proteins! It’s impossible for us to grow and reproduce without additional nitrogen sources.

Rowie: Yeah, so we start gathering all the carbons we can find and store them in the form of fats. Fatty acids are mostly made of carbon and hydrogen, so you can see why we choose to store carbons this way.

Starkey: Then we chill and hope for better times to come. It’s basically what you humans do; when you eat extra carbons, you store them as fats for future use.

Interviewer: (Looks down at himself and changes the subject) Ella, you mentioned that you microbes are not able to reproduce under nitrogen-limiting conditions. How do you feel about that?

Ella: I mean… Sometimes life sets you back and you can’t do anything about it. Obviously our dream is to become two cells—as François Jacob put it—but hey, at least we’re still alive. Motherhood is still a possibility in the future.

Starkey and Rowie: (Nods heads)

Interviewer: Nicely said. Hey, I like that color on you, by the way.

Ella: Thanks, my chlorophylls—pigments that help me make food—give me this lovely green color (5).

Interviewer: (Turning to Rowie and Starkey) So what about you two? Can you tell us a little bit about yourselves?

Starkey: Well, I’m obviously not green like Ella, but I’m round and cute!

Rowie: (Offended) Hey, being round isn’t the only way to be cute. I’m cute when I go through my filamentous phase too (6)…

Interviewer: OK, moving on. I’m sure you’ve heard about the global energy and environmental crises that we’re facing today. There is an effort to use clean and renewable energies such as solar, geothermal, and wind energies. Another example is biofuels, which are fuels derived from biomass. Biofuels used to be made from corn or sugarcanes, but the industry faced backlash once the food versus fuel controversy arose. Also, the sheer amount of resources used for growing and converting the plants to biofuels caused the final product to be more costly than its competitor, fossil fuels. Second generation biofuels was then established to close this gap by using cheap, inedible—at least for humans—agricultural byproducts and wastes (7). What are your thoughts on this?

Starkey: Well, I know some humans are trying to use me to help convert biomass into biofuels. I’m pretty good at eating sewage sludge (2), potato starch wastewater (8), monosodium glutamate (MSG) wastewater (9), and corn cob (10). By eating cheap food and making a lot of fats that can be used for biofuel production—around 63% of my dry weight—my lifestyle is applicable to second generation biofuels (2).

Rowie: People are also trying to use me for biofuel applications (6). I originally make less fats than Starkey—around 15% dry weight—but some researchers have gotten my fat content up to almost 90% through genetic engineering (3)!

Starkey: That’s impressive. They haven’t gotten very far with me because they’re still trying to figure out how to manipulate my DNA efficiently. As you may or may not know, one DNA manipulation technique doesn’t work across all yeasts. Oftentimes what works well in one species do not work well, if at all, in another. There have been some success recently (11, 12), so we’ll see if these protocols work in other labs and something useful comes out of it.

Ella: Cool. Well, I can accumulate up to 53% of my weight as fats (4). But I’m extra special because I can make my own food. All I need is some light, water, and carbon dioxide (CO₂) from the air. The light strikes the electrons donated by water, and when the electrons give up its energy, I capture it for future use. With this energy, I incorporate CO₂ into small compounds to make bigger ones, like fats. I will admit that I make more fats when I get to eat a prepared meal; making my own food is a lot of work! So people have focused on feeding me wastewater to produce fats to be used for biofuels (13, 14).

Interviewer: So do you guys think the biofuel industry will be successful?

Rowie: I mean, we’ll see. If you humans can figure out a way to keep the costs lower than fossil fuels, why not?

Ella: But honestly, we could care less about the energy crisis you guys are dealing with. We don’t drive cars or heat our homes, you know? I guess the only issue is any negative impact that processes such as drilling and fracking have on the environment.

Starkey: Yeah, please keep us in mind when you guys are about to do something that’ll hurt us and other organisms—directly and indirectly—on this planet! Believe it or not, the Earth does NOT revolve around you humans.

Interviewer: Agreed. Let’s just hope our friends in Congress know better. Any other plans tonight?

Starkey: Just returning to the soil to binge on carbons once again (11).                      

Ella: Same, except in my freshwater pond (15).

Rowie: Yep, back to your extra sharp cheddar cheese (16).

Interviewer: (Chuckles) There we have it! Thanks for joining me tonight.

Microbes: Thanks for having us!

Interviewer: (To the audience) We’ll be right back after these messages!

References

1.            Freitas RA. 1998. Human Body Chemical Composition. Nanomedicine.

2.            Angerbauer C, Siebenhofer M, Mittelbach M, Guebitz GM. 2008. Conversion of sewage sludge into lipids by Lipomyces starkeyi for biodiesel production. Bioresour. Technol. 99:3051–3056.

3.            Blazeck J, Hill A, Liu L, Knight R, Miller J, Pan A, Otoupal P, Alper HS. 2014. Harnessing Yarrowia lipolytica lipogenesis to create a platform for lipid and biofuel production. Nat. Commun. 5:1–10.

4.            Mujtaba G, Choi W, Lee C-G, Lee K. 2012. Lipid production by Chlorella vulgaris after a shift from nutrient-rich to nitrogen starvation conditions. Bioresour. Technol. 123:279–283.

5.            Dube J. 1952. Observations on a Chlorophyll-Deficient Strain of Chlorella vulgaris Obtained after Treatment with Streptomycin. Science (80-. ). 116:278–279.

6.            Qiao K, Imam Abidi SH, Liu H, Zhang H, Chakraborty S, Watson N, Kumaran Ajikumar P, Stephanopoulos G. 2015. Engineering lipid overproduction in the oleaginous yeast Yarrowia lipolytica. Metab. Eng. 29:56–65.

7.            Sims REH, Mabee W, Saddler JN, Taylor M. 2010. An overview of second generation biofuel technologies. Bioresour. Technol. 101:1570–1580.

8.            Liu JX, Yue QY, Gao BY, Wang Y, Li Q, Zhang PD. 2013. Research on microbial lipid production from potato starch wastewater as culture medium by Lipomyces starkeyi. Water Sci. Technol. 67:1802–1808.

9.            Liu JX, Yue QY, Gao BY, Ma ZH, Zhang PD. 2012. Microbial treatment of the monosodium glutamate wastewater by Lipomyces starkeyi to produce microbial lipid. Bioresour. Technol. 106:69–73.

10.         Huang C, Chen XF, Yang XY, Xiong L, Lin XQ, Yang J, Wang B, Chen X De. 2014. Bioconversion of corncob acid hydrolysate into microbial oil by the oleaginous yeast Lipomyces starkeyi. Appl. Biochem. Biotechnol. 172:2197–2204.

11.         Calvey CH, Willis LB, Jeffries TW. 2014. An optimized transformation protocol for Lipomyces starkeyi. Curr. Genet. 60:223–230.

12.         Oguro Y, Yamazaki H, Shida Y, Ogasawara W, Takagi M, Takaku H. 2014. Multicopy integration and expression of heterologous genes in the oleaginous yeast, Lipomyces starkeyi. Biosci. Biotechnol. Biochem. 79:512–515.

13.         Feng Y, Li C, Zhang D. 2011. Lipid production of Chlorella vulgaris cultured in artificial wastewater medium. Bioresour. Technol. 102:101–105.

14.         Shen Q-H, Gong Y-P, Fang W-Z, Bi Z-C, Cheng L-H, Xu X-H, Chen H-L. 2015. Saline wastewater treatment by Chlorella vulgaris with simultaneous algal lipid accumulation triggered by nitrate deficiency. Bioresour. Technol. 193:68–75.

15.         Qian H, Sun Z, Sun L, Jiang Y, Wei Y, Xie J, Fu Z. 2013. Phosphorus availability changes chromium toxicity in the freshwater alga Chlorella vulgaris. Chemosphere 93:885–91.

16.         Bankar A V., Kumar AR, Zinjarde SS. 2009. Environmental and industrial applications of Yarrowia lipolytica. Appl. Microbiol. Biotechnol. 84:847–865.