Dr Michelle M. Gehringer
Qualifications:
2004: PhD University of Port Elizabeth, South Africa.
1996: M. Sc. University of Cape Town, South Africa.
1992: B. Sc. Hons. Degree University of Stellenbosch, South Africa.
1990: B. Sc. University of Cape Town, South Africa.
How Cyanobacteria shaped the modern world
We are investigating whether ancient
Cyanobacteria species grew in shallow,
nutrient rich fresh and/or marine waters
prior to the oxygenation of the Earth’s
atmosphere during the great Oxygenation
Event (GOE). To answer this question we are
culturing modern day ancestors of ancient cyanobacterial species in reduced O2 levels and
measuring their rates of CO2 uptake and O2 generation. By observing the growth morphologies,
especially calcium carbonate and iron deposition patterns, we intend to identify additional
“footprints” indicative of fossilised cyanobacteria in the geological record dating from the
Archean geological record.
Cyanobacteria and Symbiosis
The ability of cyanobacteria to form symbiotic associations
with eukaryotes is well known. I undertook a study of the
diversity of these symbiotic cyanobacteria within the roots
of the Australian cycad species, Macrozamia, and
identified that there is no specific association between
host plant species and a specific cyanobacterial symbiont
species in plants growing in the wild. We identified the production of nodularin and a nodularin variant
by 2 endosymbiont Nostoc species and further detected the production of these toxins in planta.
Cyanobacterial toxin production
The influence of climate change on the frequency and toxicity of
cyanobacterial blooms is unknown. Cyanobacterial hepatotoxin
production appears to be closely linked to environmental stress
conditions, most notably light intensity and nutrient availability. In
association with Dr. Nicola Wannicke (IOW, Warnemünde), we are
measuring toxin production under increased levels of atmospheric CO2
in nitrogen fixing cyanobacterial species of Nodularia and Nostoc. This information will equip us with
better models with which to predict and control future cyanobacterial blooms, particularly in the Baltic
Sea.
Cyanobacterial toxicology
Toxicological studies of cyanobacterial secondary metabolites
forms an ongoing theme in my research interests. While
conducting research in South Africa, I identified a role for
glutathione peroxidase involvement in the detoxification of
microcystin in mouse liver, as well as apoptosis in microcystin
exposed gut tissue and cells. In Sydney I supervised research
focussing on BMAA, a toxic amino acid synthesised by most cyanobacterial species. We were the first
group to identify BMAA induction of Reactive Oxygen Species in rat glial and primary nerve cells, which
may contribute to the development of Alzheimer’s Disease (AD) and Amyotrophic Lateral Sclerosis (ALS).
Nitrogen fixation
The availability of nitrogen is crucial to life on earth. Elucidation of the diversity
of nitrogen fixation genes in extreme environments may offer greater insights
into the origins of this important biological pathway. I supervised the
investigation of the diversity of nifH genes in the stromatolites of Shark Bay and
Paralana Hot Springs, Australia. Dr Will Cuddy investigated the potential benefits
of cyanobacteria on the growth of wheat plants during the course of his PhD.
Publications
1. Gehringer, M. M., Downs, K. S., Downing, T. G., Naudé, R. J., Shephard, E. G. (2003) An
investigation into the effect of selenium supplementation on microcystin hepatotoxicity.
Toxicon 41:451-458.
2. Gehringer, M. M., Govender, S., Shah, M., Downing, T. G. (2003) An investigation of the role
of vitamin E in the protection of mice against microcystin toxicity. Environmental Toxicology
18:142-148.
3. Gehringer, M. M., Kewada, V., Coates, N., Downing, T. G. (2003) The use of Lepidium
sativum in a plant bioassay system for the detection of microcystin-LR. Toxicon 41:871-876.
4. Gehringer, M. M., Shephard, E. G., Wiegand, C., Downing, T. G., Neilan, B. A. (2004) An
investigation into the detoxification of microcystin-LR by the glutathione pathway in balb/c
mice. International Journal of Biochemistry and Cell Biology 36:931-941.
5. Gehringer, M.M. Microcystin-LR induced cellular effects: a dualistic response. (2004) FEBS
Letters 557:1-8.
6. Botha, N., Gehringer, M.M., Van de Venter, M., Downing, T.G., Shephard, E.G. (2004) The
role of microcystin-LR in the induction of apoptosis and oxidative stress in Caco2 and MCF-7
cells. Toxicon 43:85-92.
7. Botha, N., Gehringer, M.M., Van de Venter, M., Downing, T.G., Shephard, E.G. (2004) The
influence of intraperitoneally administered Microcystin-LR on the gastrointestinal tract of
Balb/c mice. Toxicon 43:251-254.
8. Gehringer, M.M., Milne, P., Lucietto, F., Downing, T.G. (2005) Comparison of the structure
of key variants of microcystin to vasopressin. Environmental Toxicology and Pharmacology
19:297-303.
9. Downing, T.G., Meyer, C., Gehringer, M. M. and van de Venter, M (2005). Microcystin
content of M. aeruginosa is modulated by nitrogen uptake rate relative to specific growth
rate or carbon fixation rate. Environ. Toxicol. 20:257-262.
10. Downing, T. G., Sember, C.S., Gehringer, M.M. and Leukes, W. (2005) Medium N:P ratios
and specific growth rate co-modulate microcystin content in Microcystis aeruginosa
PCC7806 and M. aeruginosa UV 027. Microbial Ecology 49:1-6.
11. Wilson, A.E., Sarnelle, O., Neilan, B.A., Salmon, T.P., Gehringer, M.M., Hay, M.E. (2005)
Genetic variation of the bloom-forming cyanobacteria, Microcystis aeruginosa, within and
among lakes: implications for harmful algal blooms. Applied and Environmental
Microbiology 71:6126-6133.
12. Gehringer, M.M., Pengelly, J.J. L., Forster, P.I., Cuddy, W. S., Fieker, C. and Neilan, B.A.
(2010) Host selection of symbiotic cyanobacteria in 31 species of the Australian cycad
genus: Macrozamia (Zamiaceae). Molecular Plant-Microbe Interactions 23: 811-822.
13. Al-Tebrineh, J., Gehringer, MM, Akcaalan, R., Neilan, BA. (2011) A New Quantitative PCR
Assay for the Detection of Hepatotoxigenic Cyanobacteria. Toxicon 57: 546-554.
14. Timms, V., Gehringer, MM., Mitchell, H., Daskalopoulos, G., Neilan, BA (2011) How
accurately can we detect Mycobacterium avium subsp. paratuberculosis infection? Journal
of Microbiological Methods 85: 1-8.
15. Chiu, A.S., Gehringer, MM., Welch, J., Neilan, BA. Does α-Amino-β-methylaminopropionic
Acid (BMAA) Play a Role in Neurodegeneration? Int. J. Environ. Res. Public Health 2011, 8,
3728-3746.
16. Cuddy, WS, Neilan, BA, Gehringer, MM. (2012) Comparative analysis of cyanobacteria in the
rhizosphere and as endosymbionts of cycads in drought-effected soils. Microbial Ecology 80:
204-215.
17. Gehringer, MM., Adler, L., Roberts, A.A., Moffit, M.C., Mihali, T.K., Mills, TJT., Fieker, C.,
Neilan, B.A. (2012) Nodularin, a cyanobacterial toxin, is synthesized in planta by symbiotic
Nostoc sp. ISME (DOI:10:1038/ismej.2012.25).
18. Chiu, A., Gehringer, MM., Braidy, N., Guillemin, G., Welch, J., Neilan, BA. (2012) Excitotoxic
potential of the cyanotoxin β-methyl-amino-L-alanine (BMAA) in primary human neurons.
Toxicon 60: 1159-1165.
19. Cuddy, W.S., Summerell, B.A., Neilan B.A., Gehringer, M.M. (2013) Inoculation with Nostoc,
Microcoleus vaginatus and Leptolyngbya is detrimental to the growth of wheat (Triticum
aestivum L.) under salt stress. Plant and Soil 370: 317-332.
20. Chiu, A., Gehringer, MM., Braidy, N., Guillemin, G., Welch, J., Neilan, BA. (2013) Gliotoxicity
of the cyanotoxin, β-methyl-amino-L-alanine (BMAA). Nature Scientific Reports 3: 1482.
21. Gehringer, MM. and Wannicke, N. (2014) Climate change and regulation of toxin
production in Cyanobacteria. FEMS Microbiology Ecology 88:1-25.
22. Chiu, A., Braidy, N., Marçal, H., Welch, J., Gehringer, MM., Guillemin, G., Neilan, BA. (2015)
Global cellular responses to β-methyl-amino-l-alanine (BMAA) by olfactory ensheathing glial
cells (OEC). Toxicon 99:136 – 145.