Vicente Fernandez. Group of Prof. Roman Stocker

Transcription

1 Microbial motility in complex fluid environments Vicente Fernandez Group of Prof. Roman Stocker

2 Microbial motility in ecological context 5 70% of bacteria in the ocean are motile

3 Hotspots dominate the ocean microscale Short-lived localized concentrations of resources Smriga, Fernandez, Mitchell & Stocker, PNAS 2016 Stocker et al, Science 2010

4 Bacterial competition in a phytoplankton bloom Teeling et al. Science, 2012 Motile population dominates biomass after 4 days! Microscale, phycosphere consumption underpins initial macroscale bacterial succession Smriga, Fernandez, Mitchell & Stocker, PNA

5 Bacterial motility overview L body 1 Lµm flagella Rotational diffusion T run ~ 1 s ~ 1-5 mm V ~ mm/s Re ~ <10 ~ mm -4 T tumble ~ 0.1 s f tumble ~ 68 Random Walk

6 Chemotaxis Assay Garren, & Stocker, ISME J 2014

7 Chemotaxis towards coral mucus Migration rate << Swimming speed

8 Shapiro, Fernandez, & Stocker, PNAS 2014 The coral microenvironment Fluid flow near coral surfaces is surprisingly complicated Frequent vortices are generated by aligned surface cilia These vortices help dissipate oxygen for photosynthesis They also provide a physical immune system against pathogenic bacteria

9 Shapiro, Fernandez, & Stocker, PNAS 2014

10 Bacteria in shear flow Rusconi, Guasto & Stocker, Nature Physics, 201

11 Shapiro, Fernandez, & Stocker, PNAS 2014

12 Brumley, & Stocker, in prep Bacteria do not go with the flow 200 µm bacteria beads

13 Brumley, & Stocker, in prep Bacteria do not go with the flow Histogram (140,000 points) Biased motion Cross-streamline migration hindered by flow

14 Garren, & Stocker, ISME J 2013, Bacteria do not go with the flow Chemotactic index, I C E. coli Ben-Haim& Rosenberg, 2002 Despite these defenses, vibrio coralliilyticus infects and bleaches coral Time [s] Motility is part of the explanation

15 Garren, & Stocker, ISME J 2013, Bacteria do not go with the flow Chemotactic index, I C E. coli Time [s] Motility is part of the explanation

16 Bacillus subtilis 1 µm (Vlamakis et al. 2013) (Cisneros et al. 2007) Rod shaped Multiple flagella Run and tumble motility Flagellar bundles can form at either end 20 µm/s swimming speed (Cisneros et al. 2011)

17 Aerotaxis in B. subtilis Menolascina et al. NPJ Syst Biol Appl 201

18 Oxygen in dense suspensions O 2 dependence allows us to exert some control over individuals in an active fluid Motility enabled as oxygen increases over a threshold value Bias in behavior of individuals in response to a gradient Are active matter dynamics influenced by aerotactic behavior in individuals?

19 Tracking individual bacteria O 2 N 2 2% cells stained Phase imaging Fluorescently labeled bacteria (not simultaneous) ½ speed

20 Relationship between oxygen and collective motion Average Collective Speed (µm/s) Distance across channel (µm) Oxygen source Oxygen sink

21 Transient collective speed Average Collective Speed Distance across channel (µm) Steep Oxygen Gradient Oxygen Front µm/s Time (min)

22 Individual aerotaxis observed in dense suspensions Average Fluorescence Distance across channel (µm) Individual bacteria are affected by collective motion but still migrate towards oxygen source Migration speed um/s Time (min)

23 (Cisneros et al. 2007) Many challenges for bacteria at small scales (low Re, point measurements, rotational diffusion, high external flow) Despite this, individual bacteria are able to navigate their environments

24 Thanks! Roman Stocker Steven Smriga Orr Shapiro Filippo Menolascina Jim Mitchell Assaf Vardi Roberto Rusconi Douglas Brumley Melissa Garren