Lecture 07 Squid Bioluminescence

What form of defense do bobtails utilize with their bioluminescent bacteria ?

counterillumination, where the light from their light organs minimizes their shadow and obscures their silhouette

the scientific name for the bobtail squid is »>

Eupyrymna scolopes

How does a bobtail squid acquire symbionts?

Horizontal transmission- from the sand that they burrow in during the day

What is the symbiont of the bobtail squid ?

Gamma proteobacteria - allivibrio fischeri

in the free-living state of vibrio fischeri, they are (flagellated/nonflagellated)

flagellated

vibrio fischeri are flagellated/nonflagellated in the symbiotic state

nonflagellated

where are the gamma-proteobacteria housed ?

in the crypts of the light organ

what benefit does the gamma-proteobacteria gain from the relationship?

food and shelter

the squid-Virbrio system is an example of what kind of mutualism?

defensive

what makes a good model for symbiosis studies?

both partners culturable in a lab

short generation time

partners can be cultured apart from one another

symbiosis can be established in the lab

good genomic resources

(unique to squid-vibrio)- fast light organ development

what is the portion labelled r?

reflector that reflects light downward

what is the portion labelled is ?

ink sac; it absorbs dorsal light and can be retracted/advanced

what are the portions labelled 1,2,3

bacterial crypts

• extracellular epithelium that opens via pores to mantle cavity

• houses 10^9 bacteria per light organ

what is the portion labelled hg?

hindgut

What is the light organ made up of?

• reflector tissue

• a shutter mechanism (ink sack)

• transprent lens that covers the light organ

• yellow filter that changes color of the emitted light

the organ contains _______ receptors and can be detected by bacterial light

light

how can the squid modify the light output ?

regulating oxygen concentration

at sunrise, the squid will expel ___ % of its symbionts

90

the colonization process is fast/slow and specific

fast

what is the section labelled L ?

lens- made of mostly aldehyde dehydrogenase

• is analogous to eye lens and chrysalis

• spreads light across the squid body

Describe symbiont transmission

the squid expels 90% of its symbionts by squeezing bacteria out of pores, resulting in large free-living symbiotic populations, and buries itself in sand, where the light organ population regrows during the day.

how is the light organ in a juvenile squid different?

lacks a lens, born with ciliated epithelia and two pairs of arms on nascent light organ

what do the arms on the nascent light organ do on a juvenile ?

create currents to trap bacteria near pores in combination with mucus secretion to aggregate the bacteria

how do the arms aggregate bacteria?

the cilia of juveniles beat and direct particles to 3 pores at the base of the appendages

the light organ of the juvenile squid permits particle entry for roughly how long?

30 min

when the squid detects light from the symbionts, what happens?

the light organ matures, losing the ciliated appendages and prevents any other bacteria from entering, where any non-luminescent V. fischerii do not survive in the crypts of the light organ

What is the bacterial gauntlet?

A series of “obstacles” that weed out non- V. fischerii bacteria:

• V. fischerii has chemotaxis toward compound in squid mucous

• cilia in ducts beat outward

• high nitric oxide concentrations are a V. fischerii attractant

• bactericidal acid in crypts kills non-target bacteria

• hemocytes patrol and kill non-target bacteria and even offer themselves as additional food for target bacteria

What is the Winnowing?

the process of the bobtail squid becoming selective for V. fischeri to build up a concentration of symbionts in the light organ.