Kenta Watanabe

Laboratory of Veterinary Public HealthJoint Faculty of Veterinary Medicine

Yamaguchi University

Research on intracellular bacteriaand their hosts

Intracellular bacteria

Prevention oflysosome-phagosomefusion

Resistance tolysosomal enzymes

Escape intothe cytoplasm

BrucellaListeriaSalmonellaFrancisellaLegionella etc.

Outline of study

DiseaseInfectionReservoir

Outline of study

Legionella and protist hosts

Predacious protists

Nature environment

?

Legionellosis

The mechanisms of infection and endosymbiosis in protistan hosts are not fully understood.

Paramecium /slipper animalcule

Paramecium spp.◆ Free-living, single-celled,

freshwater ciliate.

◆ Feeding on bacteria, and foundwidely in environmental water.

◆ The cell body is 100–300µm,and roughly cigar-shaped.

Chlorella and P. bursaria Holospora spp. and P. caudatum

30m 48h 30m 48h

L. pneumophila philadelphia1-GFP E. coli-AsRed

100μm

（Watanabe et al. Sci Rep, 2016）

Legionella within Paramecium

Legionella within Paramecium

BioRecource of Paramecium

Symbiosis Type Cytotoxic TypeDigestion Type

Egestion

Legionella

Uptake

CytotoxicEffect

Cytotoxic type relationship

Philadelphia-1 Ofk308

50μm

Legionella endosymbiosis-modulating factor A

Identification of disrupted gene

Identification of transposon-inserted locus in the mutant

lpofk_01540lpofk_01539 lpofk_01541

Ofk308

↓lefA

mini-Tn5KmMutant strain

lpofk_01540

lpofk_01539 lpofk_01541

Identification of cytotoxic factor

Legionella pneumophila Ofk308(Cytotoxic type strain)

Legionella pneumophila Ofk308lefA mutant

Transposon insertion into lefA gene

Cytotoxic Endosymbiotic

Digestion system of Paramecium

Uptake

Egestion

Fusion to Acidsome

Fusion to Lysosome

lefA

spreading byhost movement

increasing therisk of infection

Killing hostcells and

escape to outside

infect newhost cells

Legionella

uptake byParamecium

appropriatecondition

inappropriatecondition

endosymbiosis

dissolutionendosymbiosis

by LefA

Conclusion

pathogenicLegionella

endosymbiosisin protist host

Legionellosis

Non-pathogenicLegionella

not succeed at endosymbiosis

succeed atendosymbiosis

low pathogenicity high pathogenicity

mutatedLegionella

・digested・killing the host cell

pathogenicLegionella

endosymbiosisin protist host

Legionellosis

Non-pathogenicLegionella

not succeed at endosymbiosis

succeed atendosymbiosis

low pathogenicity high pathogenicity

mutatedLegionella

・digested・killing the host cell

pathogenicLegionella

endosymbiosisin protist host

Legionellosis

Non-pathogenicLegionella

not succeed at endosymbiosis

succeed atendosymbiosis

low pathogenicity high pathogenicity

mutatedLegionella

・digested・killing the host cell