Bio 1-L6- Cell-cell communication

costs and benefits to multicellularity

costs

• costly to adhese and communication molecules

• physical limitaions- those in the centre of biofilms can’t move

• competition between individuals- those in the middle of biofilms don’t access nutrients

benefits

• resistance to physical/chemical stress

• resource acquisition

• protection

• colonisation

examples of group level behaviours in bacteria

• bioluminescence- aliivibrio- use AHL’s- LuxR and LuxI

• virulence- under quorum sensing

quorum sensing defintion

ability to detect and respond to population density

what are QS molecules?

autoinducers and signals- they are release when at threshold concentration

• signal expression of expression genes controlling group level behaviours

• the signal diffuses away if there is low cell density

what does quorum sensing require?

1. enzyme that makes an auto inducer/signal- Luxl

2. the actual auto inducer- gram pos uses peptides, gram neg uses N-acyl homoserine- AHL’s

3. receptor that binds to auto inducer- usually has an R- LuxR, and causes transcriptional change, and makes more autoinducer enzymes

what is a lux operon?

• for bioluminescence- AHL

• luxCDABE- five genes

what do gram negative bacteria use for QS sensing? other features

• use AHL’s

• receptor and autoinducer binding is vv speciific

• small differences allow species specific communication to own kin

other autoinducers

1. AHLs- species specific

2. atypical B-H- PQS in p.aeruginoas

3. autoinducer 2- Gram pos and gram negative- not species specific- LuxS

how do multiple different species communicate with eachother? examples!!!!!!!!!!

• via LuxS

• AHL- gram negative to have private conversation

• autoinducer 2- interspecies communication

p.aeringosa can respond but not make AI-2

quorum sensing- social trait- explain cheats and give examples

1. signal negative- doesn’t produce signal but can respond to it- LuxI negative/no AHL

2. signal blind- produces LuxI signal but doesn’t produce of products in response- LuxR negative

mutate QS genes in P. aeruginosa

• signal negative- LasL mutant- no signals made but can respond

• signal blind- lasR mutant- does produce signal but does not respond