Marine Microbiology - Algae and bacteria

What is marine biofouling

undesirable growth of micro- and macro-organisms on marine surfaces

What are affected by marine biofouling?

challenge for marine eukaryotes and fouling bacteria

detrimental to marine algae and other eukaryotes

What is Delisea pulchra?

Algae that produces unusual secondary metabolites

• rare in nature

What molecules does Delisea pulchra produce?

Halogenated furanones

under gland cells of algal tissue

What do halogenated furanones do to bacteria?

inhibit colonization by epiphytic bacteria on Delisea pulchra

→ colonization and biofilm formation by Ruegeria sp.

What is quorum sensing?

Cell-cell signaling in bacteria for colonization and biofilm formation

→ e.g. bacterial signaling molecules: N-Acyl Homoserine Lactones (AHLs)

How furanones inhibit bacterial signalling?

Furanones act as quorum sensing inhibitors

Process of furanones inhibiting bacterial signalling

How furanones shut down quorum sensing mechanism?

Penetrate Pseudomonas aeruginosa biofilms

→ shut down the quorum-sensing signalling systems and cause detachment

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(green fluorescence protein = quorum sensing on)

(red = biomass)

=> furanones shutting down quorum-sensing as conc. increase → biomass reduced

Effect of Delisea pulchra crude extract on bacterial attachment (field trial)

Inihibitory effect

Bacteria abundance compared with Furanone distribution

• Low dist of Furanone = high bacteria abundance

Furanone on bacteria diversity in diff. parts of Delisea pulchra

Furanone affect diversity?

Bacteria isolates ifrom diff. parts

BUT 1 sp. across the whole plant

What is Denaturing Gradient Gel Electrophoresis (DGGE)?

Type of Microbial community fingerprinting

1. Extract DNA

2. Amplify with PCR,separating the 16s rDNA gene from the whole microbial community - on denaturing gradient gel (urea denaturing agent, polyacrylamide gel)

→ Differences of 1 base-pair in the PCR product can be detected

1 band type = 1 species

What is Multidimensional Scaling?

Stat. method used to visualise difference in data

Results of Multidimensional Scaling

Diff microbial comm. at diff regions of plant

D. pulchra's effect on the community succession

Field array apparatus measuring community succession of D. pulchra

Secure treated algae/inanimate surfaces in the marine environment for extended periods

Field assay of microbial community over time on Delisea pulchra

Antibiotic treated v.s. control

Bacterial succession on D. pulchra (tip)

After 12 days, microbial community was reintroduced to the antibiotic-treated D. pulchra

→ D. pulchra control bacteria community on the surface

What Furanone production do to bacteria community?

Furanone production can prevent fouling and control bacterial community succession on the surface of Delisea pulchra

Anti-biofouling strategies with Furanone

Environment and medical usages

Other non-chemical defence against biofouling (e.g. Ulva lactuca & Pseudoalteromonas)

Harbours inhibitory bacteria such as Pseudoalteromonas

What is Pseudoalteromonas tunicata ?

Colonizes marine living surfaces (e.g. Ulva lactuca)

• Produces a range of bioactive compounds that inhibit marine fouling organisms (e.g. invertebrate larvae, algal spores)

How Pseudoalteromonas tunicata defends against biofouling?

produces a range of target-specific extracellular inhibitory compounds

Antibacterial protein of P.tunicata

AlpP

Size: 190 KDa

Mode of action: lysine oxidase activity, H2O2 production

Detected in the effluent of biofilms ≥ 3 days old.

Does P. tunicata outcompete other marine bacterial strains  during competitive biofilm development?

Yes

A  P. tunicata ΔalpP mutant strain exhibits reduced ability to compete against P. gracilis

Testing Competitive biofilm development by epiphytic bacteria

How marine plants (not D. plunra) defend against fouling?

Bacteria on marine plant surfaces can produce extracellular inhibitory compunds