Scientific Highlight October 2012

Transcription

1 Scientific Highlight October 2012 Research Unit Microbe-Plant Interactions (AMP) PSP-Element: G Person to contact for further enquiries: Prof. Dr. Anton Hartmann, Tel Dr. Michael Schmid, Tel Title of the Highlight: Out of the ground: Aerial and exotic habitats of the melioidosis bacterium Burkholderia pseudomallei in grasses in Australia Keywords: Microbe-plant interactions, human pathogens, FISH-CLSM, emerging infectious diseases Central statement of the Highlight in one sentence: Grasses could act as ecological niche for the human pathogenic bacterium Burkholderia pseudomallei, the causing agent of mellioidodis. Text of the Highlight: Melioidosis is an emerging infectious disease of humans and animals in the tropics caused by the soil bacterium Burkholderia pseudomallei. Despite high fatality rates, the ecology of B. pseudomallei remains unclear. We used a combination of field and laboratory studies to investigate B. pseudomallei colonization of native and exotic grasses in northern Australia. Multivariable and spatial analyses were performed to determine significant predictors for B. pseudomallei occurrence in plants and soil collected longitudinally from field sites in Northern Australia. In plant inoculation experiments, the impact of B. pseudomallei upon these grasses was studied and the bacterial load semiquantified. Fluorescence in situ hybridization and confocal laser scanning microscopy were performed to localize the bacteria in plants. Burkholderia pseudomallei was found to inhabit not only the rhizosphere and roots but also aerial parts of specific grasses endophytically. Publication: Kaestli M., Schmid M., Mayo M., Rothballer M., Harrington G., Richardson L., Hill A., Hill J., Tuanyok A., Keim P., Hartmann A., and Currie B.J. (2012). Out of the Ground: Aerial and Exotic Habitats of the Melioidosis Bacterium Burkholderia pseudomallei in Grasses in Australia. 1

2 Taking account of the HMGU mission: The study demonstrates the evidence that plant roots and other plant tissues could act as natural reservoirs for human pathogens. We demonstrate the correlation between grasses and the increased occurrence of mellioidosis in so far non endemic regions in the Northern territory of Australia. The study contributes to a better understanding of the ecology of human pathogens in plant habitats and to a healthy environment for human beings. The internal HMGU co-operation partners with whom the Highlight was compiled, if appropriate: - 2

3 Out of the ground: Aerial and exotic habitats of the melioidosis bacterium Burkholderia pseudomallei in grasses in Australia Helmholtz Zentrum München Department Microbe-Plant Interactions PSP: G

4 Introduction, aims of the study AMP Introduction: Mellioidosis is an emerging infectious disease affecting humans and animals. It is caused by the soil bacterium Burkholderia pseudomallei. Mellioidosis is endemic in tropics of South-East-Asia and Northern-Australia Mode of infection: Percutaneous inoculation (through a cut in the skin, e.g. while gardening or rice farming) or inhalation (e.g. after heavy rains in the wet season). Risk factors for infection are diabetes, alcoholism and renal or lung diseases Symptoms range from subclinical infection to localized abscess formation (e.g. skin or internal organ) to pneumonia and systemic sepsis (high mortality rates up to 90%) The natural habitat of B. pseudomallei is still unknown Aim of the study: Investigation of the B. pseudomallei-grass interaction in Northern Australia. Are grasses an ecological niche of pathogenic bacteria and could act as a reservoir for B. pseudomallei? Studies were performed on natural grass samples and on artificial inoculated grasses Determination of the colonization behavior of B. pseudomallei on different grasses using microscopic (fluorescence in situ hybridization [FISH] in combination with confocal laser scanning microscopy [CLSM]) and molecular methods (qpcr).

5 Endemic regions, sampling sites Endemic regions of B. pseudomallei Paspalum grass was introduced to the Top End of Australia in the 20 th century as a pasture grass. sampling sites in the Northern Territory Mission grass was introduced to the Top End of Australia in the 20 th century as a pasture grass and is now a declared weed.

6 In situ detection of B. pseudomallei cells in roots and arial parts of different grasses AMP BET-42a_Cy5 A Bpm-463-Cy3 BET-42a_Cy5 B Bpm-463-Cy3 B. pseudomallei inhabits not only the rhizosphere, but also roots and aerial parts of various grasses. FISH/CLSM images: A: B. pseudomallei in stomatal guard cells of Paspalum grass (Paspalum plicatulum) leafs and B in cortex root cells of Mission grass (Pennisetum pedicellatum).

7 Real-time PCR targeting B. pseudomallei specific TTS1 AMP Roots of Paspalum grasses of field site Leaves of these Paspalum grasses Grass roots and leaves postive for B. pseudomallei by qpcr (approx. 6,000 TTS1 copies in roots, in leaves) Roots and leafs od different grasses in the Northern territory of Australia could be colonized endophytically by the bacterium Burkholderia pseudomallei.