{"id":21552,"date":"2014-07-22T03:12:45","date_gmt":"2014-07-22T01:12:45","guid":{"rendered":"https:\/\/renewable-carbon.eu\/news\/?p=21552"},"modified":"2014-07-21T18:25:20","modified_gmt":"2014-07-21T16:25:20","slug":"ocean-microbes-display-hidden-talent-releasing-countless-tiny-lipid-filled-sacs","status":"publish","type":"post","link":"https:\/\/renewable-carbon.eu\/news\/ocean-microbes-display-hidden-talent-releasing-countless-tiny-lipid-filled-sacs\/","title":{"rendered":"Ocean microbes display a hidden talent: releasing countless tiny lipid-filled sacs"},"content":{"rendered":"

In the search for a renewable energy source, systems using algae look like a good bet. Algae can grow quickly and in high concentrations in areas unsuitable for agriculture; and as they grow, they accumulate large quantities of lipids, carbon-containing molecules that can be extracted and converted into biodiesel and other energy-rich fuels. However, after three decades of work, commercially viable production of biofuels from algae hasn\u2019t been achieved, in part because the processes needed to break apart the algae and recover the lipids are costly and energy-intensive.<\/strong><\/p>\n

Another option is to use bacteria. For the past 25 years, Sallie (Penny) Chisholm, the Lee and Geraldine Martin Professor of Environmental Studies, has been studying Prochlorococcus<\/em>, an ocean-dwelling bacterium that she calls \u201ca pretty spectacular organism.\u201d Of all organisms that perform photosynthesis, this single-celled bacterium is both the most abundant and the smallest \u2014 less than 1 micron in diameter. It accounts for fully 10 percent of all photosynthesis on Earth and forms the base of the ocean food chain. It also has the smallest genome of any known photosynthetic cell.<\/p>\n

\u201cThree billion years of evolution has streamlined its genome, and it now contains the least amount of information that can make biomass from solar energy and carbon dioxide,\u201d says Chisholm, who has a joint appointment in civil and environmental engineering (CEE) and biology. \u201cIt makes sense that we try to understand it \u2014 inspired by its simplicity \u2014 and see if we can use this understanding to help us design microorganisms that efficiently produce biofuels directly from sunlight.\u201d<\/p>\n

\"20140611-ef-ocean-microbes-3_0\"
This scanning electron micrograph shows cells of a lab-cultured strain of Prochlorococcus plus small, spherical vesicles (indicated by arrows), which are released by the cells as they grow. This is the first time vesicle formation and release have been detected in a marine organism or in an organism that performs photosynthesis. The vesicles contain DNA, RNA, a variety of proteins, and lipids \u2014 molecules that potentially could be used to produce biofuels.<\/figcaption><\/figure>\n

In 2010, Chisholm\u2019s much-studied bacterium delivered a surprise: As it grows, it naturally releases small, spherical, membrane-bound vesicles containing fatty oils related to those that make algae so appealing. This was a serendipitous discovery. In 2008, Chisholm\u2019s group needed some images of Prochlorococcus<\/em> for a publication. Using a scanning electron microscope, then-graduate-student Anne Thompson PhD \u201910 took the images \u2014 and they showed small spheres near the surfaces of the Prochlorococcus<\/em> cells. The spheres remained a mystery to the ocean biologists until 2010, when Steven Biller joined Chisholm\u2019s group as a postdoctoral associate in CEE. Based on his work with soil bacteria, he proposed \u2014 and subsequently confirmed \u2014 that the spheres are lipid-bound vesicles.<\/p>\n

That finding is remarkable for two reasons. While many species are known to release vesicles, the behavior has never before been observed in a marine organism\u2014and it could significantly change today\u2019s understanding of marine ecosystems, including their influence on the global carbon cycle. \u201cProchlorococcus is making organic carbon from sunlight and then packaging it up and releasing it into the seawater around it,\u201d says Chisholm. \u201cWhat we need to figure out now is, Why and how? And what role do these vesicles play in ocean food webs and the ocean carbon cycle?\u201d<\/p>\n

Equally surprising, this is the first observation of vesicle release in an organism that performs photosynthesis. The implications for industrial use \u2014 including biofuels production \u2014 are significant. Given just sunlight, carbon dioxide, and water, Prochlorococcus<\/em> would continually release lipid-containing vesicles, which could be collected without disturbing the growing bacteria. \u201cWith algae, retrieving the lipids requires destroying one batch of cells and starting with a new batch,\u201d says Biller. \u201cWith Prochlorococcus<\/em>, it could be a \u2018continuous culture.\u2019\u201d<\/p>\n

Technical challenges, new insights<\/h3>\n

Chisholm stresses that such commercial applications are \u201cway down the road.\u201d For now, research in her lab focuses on developing a fundamental understanding of the newly observed behavior. For example, how often does a Prochlorococcus<\/em> cell release vesicles? How many does it release? And what\u2019s inside them?<\/p>\n

To answer those questions, Biller overcame a series of technical challenges. First he developed improved methods of culturing large quantities of Prochlorococcus<\/em> cells. Then he designed techniques for filtering off the vesicles and concentrating and purifying them \u2014 while keeping them intact. But his biggest problem was how to count the individual vesicles. Standard methods of counting particles don\u2019t provide sufficient resolution to look at the vesicles, which are less than 100 nm in diameter. After some trial and error, Biller was successful in adapting recent advances in nanoparticle analysis techniques to studying these tiny bacterially derived structures.<\/p>\n

\"Bildschirmfoto
Figure 1: Vesicle production by Prochlorococcus. These curves indicate Prochlorococcus cells and vesicles present in samples taken daily from one lab-cultured strain of the bacterium. Cell concentrations are noted by solid squares; vesicle concentrations are noted by open circles. Based on similar tests with three different Prochlorococcus strains, the researchers estimate that the rate of release varies from two to five vesicles per cell per generation.<\/figcaption><\/figure>\n

Using his new approaches, he determined that vesicles are present in large concentrations in growing cultures. Indeed, they outnumber the Prochlorococcus<\/em> cells themselves \u2014 in some cases by a factor of 10 (see Figure 1). They are generated by strains of Prochlorococcus<\/em> that grow in bright light (such as near the ocean surface) as well as in dimmer light (typical of the deep ocean). Vesicles appear to be produced continually during some phases of cell growth, and they are stable under laboratory conditions: Over the course of two weeks, the size and concentration of vesicles in a laboratory culture remained essentially unchanged. Finally, the vesicles contain not only lipids but also DNA, RNA, and a diverse set of proteins.<\/p>\n

Unfortunately, the lipids in the vesicles from Prochlorococcus<\/em> are not the optimal kind for making biofuels, notes Biller. \u201cBut because of its simple genome, it\u2019s a good model for us to use in exploring the mechanisms that control the formation and extrusion of vesicles and determine their content,\u201d he says. \u201cOnce we understand how it works, that mechanism could eventually be utilized in more robust and fast-growing organisms, and the contents of the vesicles could be manipulated.\u201d<\/p>\n

Fieldwork expands the options<\/h3>\n

Based on their laboratory data, the researchers estimated that Prochlorococcus<\/em> worldwide could release on the order of 1,027 vesicles per day \u2014 a significant contribution to the marine ecosystem. But many factors could influence vesicle production in the wild, so the team decided to take direct measurements. They collected hundreds of liters of seawater in two locations: the nutrient-rich coastal waters of Vineyard Sound in Massachusetts and the nutrient-sparse waters of the Sargasso Sea near Bermuda. They used their laboratory techniques \u2014 scaled up to handle larger volumes of water \u2014 to test the samples on board research vessels. As with their lab cultures, they found numerous vesicles in the samples from both types of ocean environments. And their analyses showed that the vesicles contained DNA from many kinds of bacteria\u2014not just Prochlorococcus<\/em>.<\/p>\n

That finding potentially extends vesicle production to organisms that are ubiquitous in ocean systems extending from pole to pole. \u201cThis adds a whole new dimension to marine microbial ecosystems that we hadn\u2019t realized was there,\u201d says Biller. \u201cAnd while Prochlorococcus was our entry point into this concept for biofuels production, it looks like there may be applications to many other organisms.\u201d<\/p>\n

Wasteful behavior?<\/h3>\n

An intriguing question is why Prochlorococcus<\/em> would make and release vesicles. Jettisoning their hard-earned organic carbon seems inconsistent with the need for this streamlined organism to make efficient use of scarce resources. What function could the vesicles serve? Biller and Chisholm don\u2019t have an answer to that question, but they\u2019ve come up with several hypotheses \u2014 ideas with potential impacts on both understanding marine ecosystems and developing commercial-scale biofuels systems.<\/p>\n

\"Bildschirmfoto
Figure 2: Growth of a marine heterotroph \u2014 a nonphotosynthetic organism \u2014 in three lab cultures. “Organic carbon mix\u201d is a mix of organic carbon compounds; “Vesicles” includes only added Prochlorococcus vesicles; and “Control” has no fixed carbon. Optical density (OD) estimates cell concentrations in liquid cultures. Data show the vesicles alone provide enough nourishment for cells to increase in number over 50 hours. Prochlorococcus thus appears to facilitate heterotroph growth.<\/figcaption><\/figure>\n

In working with Prochlorococcus<\/em>, Chisholm and her colleagues have found that the bacterium is \u201chappier\u201d in the company of heterotrophs \u2014 organisms that can\u2019t synthesize their own food and need a source of organic carbon to grow. \u201cWe went through heroic efforts to separate the Prochlorococcus<\/em> and their heterotrophic friends in seawater samples,\u201d says Chisholm. \u201cThen we realized that when we grow them together, the cultures grow faster and are more stable.\u201d In a series of experiments, Biller showed that the newly identified lipid vesicles can serve as nutrients for the heterotrophs (see Figure 2).<\/p>\n

What does Prochlorococcus<\/em> get in return? It is not fully understood, but others have shown that in the process of becoming streamlined, Prochlorococcus<\/em> lost certain enzymes that other species use to neutralize toxic oxygen compounds produced during metabolism. The heterotrophs can perform that detoxification task, taking care of the problem for Prochlorococcus<\/em>.<\/p>\n

\"Bildschirmfoto
Defense against viral predators: Transmission electron micrograph of a phage attached to a vesicle. The shortened tail of the phage suggests that it has injected its DNA, rendering it unable to infect again. The surface of each vesicle includes protein receptors from its parent cell that serve as a target for phage. The vesicles thus act as a decoy, diverting phage away from the Prochlorococcus cells.<\/figcaption><\/figure>\n

Another hypothesis is that the vesicles help protect Prochlorococcus<\/em> from phage, viruses that infect bacteria. The surface of a vesicle contains material from the outer membrane of its parent cell, including protein receptors that phage use to identify their \u201cprey.\u201d The vesicles therefore may serve as a decoy \u2014 \u201cmuch as a fighter jet trying to evade an incoming missile may throw out chaff so that the missile goes after the chaff instead of the jet,\u201d says Biller. To test that idea, Biller mixed purified Prochlorococcus<\/em> vesicles with a phage known to infect the Prochlorococcus<\/em> source of the vesicles. Electron micrographs revealed many phage attached to vesicles. Moreover, their shortened tails suggest that they have injected their DNA into the vesicles, thereby becoming inactive.<\/p>\n

A final hypothesis is that the vesicles assist in the exchange of genetic material between individual bacteria \u2014 a phenomenon known to occur in some bacteria as a means of developing genetic diversity and sharing useful genes. \u201cWe know that bacteria are swapping genes among themselves at surprisingly high frequencies \u2014 maybe by using phage or direct cell-to-cell contact,\u201d says Biller. \u201cBut it wasn\u2019t clear that those mechanisms alone could explain the apparent rates at which genes are moving around. This is one possibility of another way that DNA might be exchanged in these communities.\u201d<\/p>\n

Benefits of multiple-scale study<\/h3>\n

The researchers\u2019 latest results confirm the validity of Chisholm\u2019s decades-long approach to studying Prochlorococcus<\/em>. \u201cOur studies of this bacterium have ranged in scale from genes to cells to populations and then to the community they\u2019re embedded in and up to the global scale,\u201d she says. That approach, called integrative systems biology, has obvious benefits for understanding global ecosystems and \u2014 in the longer term \u2014 for developing practical systems involving mass cultures that are fast-growing, stable, and productive. Says Chisholm, \u201cStudying model systems such as Prochlorococcus<\/em> in an expansive sense \u2014 from the phage that infect them to the other microbes that they grow with in nature \u2014 will ultimately have relevance for any kind of large-scale production of biomass for biofuels and other types of high-energy compounds.\u201d<\/p>\n

This research was supported by grants from the MIT Energy Initiative Seed Fund Program; the Gordon and Betty Moore Foundation; and the National Science Foundation\u2019s Center for Microbial Oceanography: Research and Education and its Biological Oceanography Program.<\/p>\n","protected":false},"excerpt":{"rendered":"

In the search for a renewable energy source, systems using algae look like a good bet. Algae can grow quickly and in high concentrations in areas unsuitable for agriculture; and as they grow, they accumulate large quantities of lipids, carbon-containing molecules that can be extracted and converted into biodiesel and other energy-rich fuels. However, after […]<\/p>\n","protected":false},"author":59,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"","nova_meta_subtitle":"","footnotes":""},"categories":[5572],"tags":[],"supplier":[1936,1144],"class_list":["post-21552","post","type-post","status-publish","format-standard","hentry","category-bio-based","supplier-massachusetts-institute-of-technology","supplier-national-science-foundation-usa"],"_links":{"self":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/21552","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/users\/59"}],"replies":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/comments?post=21552"}],"version-history":[{"count":0,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/21552\/revisions"}],"wp:attachment":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/media?parent=21552"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/categories?post=21552"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/tags?post=21552"},{"taxonomy":"supplier","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/supplier?post=21552"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}