WIDE ANGLE: IM Interview -- Science of Superorganisms

The scoop: We tend to think of microbes as primitive and simple life forms. But researchers are discovering they are anything but. New experiments are revealing how microbes in the sea and elsewhere appear to act in concert, rather than alone. To coordinate their actions, microbes must have ways to communicate between cells. They even seem to answer calls to die on command to save the larger population -- just like cells do in the body of a large animal. This sort of microbial "super" organism behavior might be happening in other habitats -- like our own bodies, as researchers Kay Bidle and Vardi Assaf of Rutgers University explain...

LarryO': Hello! Let's see if your colleague logs in.

Kay Bidle: Hey. Assaf is currently in my office. He was going to sit with me in my office. He went to get his laptop. Is that OK?

LarryO': Great. That'll work. I'm pretty sure we can get this to work three ways.

Kay Bidle: Is there anything that you want to ask me while we are waiting for Assaf? To get the ball rolling?

LarryO': Sure. Let me start with what caught my attention. I've seen a few papers out recently that seem to imply there's a lot more going on among single-celled organisms in the sea than folks have thought. Almost like superorganism behaviors. Seems to challenge a lot of the ways we think about plankton.

Kay Bidle: Yes, single celled organisms were long thought to be quite evolutionarily simple and not possess sophisticated communication/signaling mechanisms that can impact an entire population. But colleagues have now discovered that this isn't really true. It started first with discoveries in bacteria--with the concept of 'quorum sensing' and how it regulates bioluminescence, or the production of cold light. This was discovered over a decade ago. It is a way that single-celled organisms can sense the presence of other cells and essentially communicate with them and even influence the coordinated expression of specific genes in response to different cues. Now, we are discovering that marine phytoplankton use similar mechanisms and these processes likely go on in the oceans everyday.

LarryO': So these "simple" creatures are sending signals to each other in order to survive better as a larger unit?

Kay Bidle: Essentially, yes. It does open the possibility that these signals/factors allow us to view these single-celled populations in a larger coordinated context...more multicellular like. As I mentioned, this has been shown for bacteria in relation to a variety of processes (light production, stress responses, virulence, etc.) Whether phytoplankton (or marine bacteria) use them in cooperation in the ocean context is not known, but it is a hot area of research right now. It is Assaf's area of expertise and he has been working on this type of thing in phytoplankton --a pioneer!-- for many years to assess these processes/strategies may influence or control bloom dynamics. BTW- Assaf couldn't get it to work, so he's sitting next to me and we are discussing our answers (hope that's OK).

LarryO': That's fine. If he wants to jump in, that's great. Can you guys give me some examples of this signaling, or its impacts, that folks might have seen or heard about?

Kay Bidle: From both of us...One awesome example of signaling is bioluminescence. You probably know that many invertebrates and fishes have light organs and give off cold, blue light. These light organs are essentially bioreactors of a single species of bacteria, with the genetic capability (possesses the necessary genes) to produce light. The light is only produced when the bacteria reach a certain cell density and then the Lux cassette (genes responsible for producing light) are turned on. In order to sense the cell density, the bacteria use signaling molecules, known as acyl homoserine lactones (AHL). These compounds diffuse in/out of cells and when the cell density is high, they accumulate in higher concentration and diffuse into cells. In doing so, they can turn on the expression of the lux cassette. So, this process is going on inside of the light organs of fish and the fish try to keep their cultures of bacteria at the right density. Make sense?

LarryO': Weird! So fish without enough of these bacteria can't light up, which means....what?

Kay Bidle: Well, then you get into the reasons that they have bioluminescence....to escape predators, to attract mates, to communicate with each other...think about that one for a minute...fish and invertebrates communicating with each other, based on bacterial communication with each other inside of their light organs ; ) So this strategy is important to the ecology of these fishes and inverts. Another example is virulence. In some pathogens, the production of their toxins is regulated in a similar way. They won't produce it until there is a critical density of bacteria.

LarryO': So this has big implications in medicine as well?

Kay Bidle: Absolutely! The more we can understand about how pathogenic bacteria regulate the expression of toxins, virulence factors, etc. the more we can better fight infections, etc. I should point out that this field is in the beginnings and there are likely many more processes that are controlled in this manner. We are trying to find out how these processes work for single-celled populations in the oceans, as they sense their environment and respond to changing conditions and influence their success in the oceans. I should add that these processes are also key for understanding how 'healthy' microbial communities interact with hosts. We just had a seminar speaker from the Univ of Maryland Biotech Inst.--Center of Marine Biotechnology in Baltimore, MD talk about their efforts to understand signaling in relation to their symbiotic relationship with tropical sponges.

Vardi Assaf: So it is now a major target for biomedical research since once you understand communication of quorum sensing you can interrupt with it. There are new groups of molecules that are termed quenchers so they have the potential to interfere with the virulence of certain bacteria.

LarryO': Wow. This really sounds like a paradigm shift underway. Is that an overstatement?

Kay Bidle: Yes, it is absolutely a paradigm shift. Especially as it relates to some of the things that we study in the lab here at Rutgers and natural phytoplankton blooms in the oceans....the triggering of programmed cell death mechanisms (apoptosis) in unicellular phytoplankton in response to virus infection, nutrient stress, etc. It allows us to invoke signaling and communication in a way that may involve selection on the population level--something that is really impossible without signaling molecules like these.

LarryO': I was going to ask about phytoplankton blooms. I'll wait for Assaf to finish.

Vardi Assaf: Many of pathogen bacteria make biofilm composed of dense population encapsulated in polysaccharide matrix as part of their life cycle. For example Microbial pathogenesis in cystic fibrosis, they make mucoid .... so the target is to break it down using quenchers, it also true for plant-pathogenic bacteria

LarryO': So this is an entirely different way to attack bacteria -- beyond antibiotics?

Vardi Assaf: That is the new antibiotic

LarryO': Amazing stuff. Very exciting and sure is nice to here, given how I'm always worried about drug resistant bacteria infecting my two children.

Kay Bidle: Yes, exactly. It is a new approach. And perhaps even more importantly, it is a novel mode of action (MOA) against bacteria, which is important because often a variety of MOAs is needed to effectively fight bacterial infections. In our current climate of antibiotic resistance, this is a very important development.

Vardi Assaf: Bacteria is so sophisticated that it has the capability to recognize friend or foe using a wide array of these molecules

Kay Bidle: The specificity of interactions and awareness are in the molecules..the chemistry

LarryO': I'm going to have to run at :15 after to pick up my kids. But I wanted to ask about "red tides." Do they have a lot to teach us in this way as well?

Vardi Assaf: I think that we should try similar approaches by under standing chemical communication to use it for future mitigation such toxic blooms.

Kay Bidle: I definitely think so. Signaling and communication in red tides is currently unexplored. Assaf has done some work on similar organisms. Given that some dinoflagellates (emphasis...some, not all) produce toxins that can lead to paralytic shellfish poisoning, etc., their toxin production may also be linked to cell density and signaling. We are interested in how it might interact with processes that lead to bloom crashes, as a potential mechanisms of terminating harmful algal blooms.

Vardi Assaf: If we isolate chemical cues (or infochemicals) like are produced by one species and suppress other target species (e.g. toxic), we can potentially use this natural product to regulate red tides.

LarryO': Swimming in the ocean will never seem quite the same to me. So much going on in the water at a microscopic level affecting such a large volume of water.

Vardi Assaf: Furthermore, since we study conservation of the genetic program regulate cell death from unicellular to multi.. and we do isolate such infochemicals that control cells fate we also get marine natural agents that has great potential for cancer research.

Kay Bidle: Oh yeah. Our major challenge as marine microbial people is to illuminate how much amazing stuff happens in the oceans among microscopic organisms. Phytoplankton, bacterial and viruses account for >90% of all oceanic biomass. (Unlike the 'charismatic megafauna'...whales, sharks, etc. that get all the attention and account for a very small amount of what lives there). They are what makes the oceans work. And they have been evolving in the oceans from the very beginning (some with >3 billion-yr-old evolutionary history). They have evolved amazingly complex and sophisticated strategies that we can learn from.

LarryO': Thanks. I apologize for cutting this short. I'll be in touch soon about perhaps putting together a slideshow or other media to expand on this conversation. That sound good?

Kay Bidle: Sounds great with me. I enjoyed it and had fun. Thanks for the invite. Keep in touch.

Vardi Assaf: Cool I have some video clips of communicating phytoplankton, thanks. Assaf

LarryO': Wonderful. Sounds like we have several good ways to tell this story. Bye for now.

Article posted February 23, 2009.

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