Monday, September 25, 2017

BacterioFiles 311 - Synchronized Slimes Spread Slowly

Bacillus subtilis colonies
By Debivort, CC BY-SA 3.0
This episode: Separate groups of bacteria can each thrive better when they take turns growing instead of competing!

Thanks to Jintao Liu and Rosa Martinez-Corral for their contributions to this episode!

Download Episode (14.2 MB, 15.5 minutes)

Show notes:
Microbe of the episode: Palyam virus

News item

Journal Paper:
Liu J, Martinez-Corral R, Prindle A, Lee DD, Larkin J, Gabalda-Sagarra M, Garcia-Ojalvo J, Süel GM. 2017. Coupling between distant biofilms and emergence of nutrient time-sharing. Science 356:638–642.

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    Episode outline:
    Background: Living in community is helpful in various ways
    Help each other, specialization, combined effort
    Also time-sharing: taking turns using some shared resource
    Examples: owning piece of expensive equipment as group, taking turns using it
    Like tiller or wood chipper for gardening/landscaping
    Or owning building/property as group and taking turns using it for vacations
    Or sharing computer resources (public terminals at library, or server capacity)
    Bacteria often live in complex communities too, like in soil
    Many different species separated by very different microenvironment conditions
    What’s new: Now, Jintao Liu, Rosa Martinez-Corral, Arthur Prindle, Dong-yeon Lee, Joseph Larkin, Marcal Gabalda-Sagarra, Jordi Garcia-Ojalvo, and Gurol Suel, publishing in Science have discovered that even far away groups of bacteria can communicate and engage in time-sharing with each other!
    Methods: Grew biofilms of Bacillus subtilis with glutamate limitation
    Essential source of nitrogen/amino acid
    Growth oscillates: grows, glutamate can’t penetrate as much, growth slows
    Then glutamate penetrates more and growth picks up again
    Cells can communicate to coordinate growth with electrical signaling
    Potassium ion channels
    Wondered if neighboring biofilms, groups of bacteria, could be affected by signaling too
    Thereby communicating and maybe cooperating while also competing for nutrient
    Set up chamber with biofilm on each side and 2mm channel between
    Monitored growth by microscopy, and had fluorescent dye that measured electrical signals
    Did indeed see growth on both sides followed by stalling and fluorescence, then repeat
    Synchronized pattern, little difference over at least 10 hours
    Not very efficient use of nutrient if both growing at same time though
    Made Math model of system
    This is the second author, Rosa Martinez-Corral, describing the goal of the modeling
    predicted that lower concentrations of glutamate could change dynamic
    Groups stop growing more; randomly one will stop growing first
    Then second will grow longer before stopping, increasing difference between them
    Less communication to synchronize, so end up out of sync; each stops as other starts
    Tested predictions with real cells
    Higher glutamate indeed had synchronization
    25% lower had opposite behavior
    How does communication affect system? Used mutants with less electrical sensing ability
    Much harder to synchronize groups; even at 50% increased glutamate
    At doubled glutamate they synchronized
    So communication important
    Also harder to synchronize when using mutants that can’t make own glutamate
    Higher requirements, effectively more limitation
    What is benefit from sync or out of sync?
    Actually groups grew better together when out of sync
    though each gets less than they would on their own
    Seems surprising, but makes sense:
    If like I Love Lucy, chocolates passing by on conveyor, four at a time
    Person on each side; have to finish chewing/swallowing what they take to get more
    If each takes 2, only get 2 at a time and miss out while chewing
    But if take turns chewing, 1 gets 4 and then other gets 4, so both get more overall
    In this case, take turns when number is reduced, so each gets 3
    Still more than just 2; better for both even though smaller number
    Specifically, going to grow and then stop anyway
    At higher glutamate, compete for same resource, split 50/50 then both stop and let pass
    At 25% lower, take turns taking what’s flowing, each gets 100%
    Though only 75% total, better than 50% from competition
    Next question: why not time-share at higher concentrations too, if it’s better?
    Not entirely clear
    Could be trade-off: bacteria can coordinate behavior but at cost of efficiency
    Doesn’t matter as much with higher nutrients, still getting enough though not as much
    Worth it for cooperation benefits, like coordinating sporulation or responses
    But at lower nutrients, more beneficial to be more efficient
    Summary: Here’s the first author, Jintao Liu, summarizing the research
    Applications and implications: Synthetic biology
    Tighter control of groups (sync or out of sync)
    or efficiency (out of sync)
    For industrial processes etc
    Understanding/control of microbiota or pathogens
    Growth could increase even if nutrient decreases? counterintuitive
    What do I think: Works with same kind of microbes; what about combo of different?
    Some do communicate/cooperate, others more competitive
    No reason why same kind of dynamic couldn’t work with different kinds
    Work together instead of competing, everyone wins!

    Rosa Martinez-Corral:
    In order to explore how communication between a pair of biofilms and their competitions for nutrients act together, we built a simple mathematical model. This model included the key point we thought to be involved in the biofilm oscillations and their coupling. And allowed us to test in the computer what would happen in case of changes in nutrient concentrations or mutations. In this way, we could test hypotheses in a much faster and cheaper way than experimentally, thus making the research more effective.

    Jintao Liu:
    Biofilms resemble multicellular organisms. However it is unclear whether a biofilm behaves as an independent functional unit. We studied this question in the context of multiple biofilms. We thought that coupling between biofilms leads to synchronized dynamics. Interestingly, in the face of nutrient competition, they can resume their independence and switch to time-sharing of resources, which leads to relieving of nutrient limitation. From a broader perspective, competition for limited resources is a common problem. It will be interesting to see if other systems in biology also utilize time-sharing strategy.

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