Susan J. Murch

Bio: Susan J. Murch is an academic researcher from University of British Columbia. The author has contributed to research in topics: Somatic embryogenesis & Hypericum perforatum. The author has an hindex of 48, co-authored 165 publications receiving 8177 citations. Previous affiliations of Susan J. Murch include University of Guelph & National Tropical Botanical Garden.

Diverse taxa of cyanobacteria produce β-N-methylamino-l-alanine, a neurotoxic amino acid

Abstract: Cyanobacteria can generate molecules hazardous to human health, but production of the known cyanotoxins is taxonomically sporadic. For example, members of a few genera produce hepatotoxic microcystins, whereas production of hepatotoxic nodularins appears to be limited to a single genus. Production of known neurotoxins has also been considered phylogenetically unpredictable. We report here that a single neurotoxin, β-N-methylamino-l-alanine, may be produced by all known groups of cyanobacteria, including cyanobacterial symbionts and free-living cyanobacteria. The ubiquity of cyanobacteria in terrestrial, as well as freshwater, brackish, and marine environments, suggests a potential for wide-spread human exposure.

Biomagnification of cyanobacterial neurotoxins and neurodegenerative disease among the Chamorro people of Guam.

Abstract: We here report biomagnification (the increasing accumulation of bioactive, often deleterious molecules through higher trophic levels of a food chain) of the neurotoxic nonprotein amino acid β-methylamino-l-alanine (BMAA) in the Guam ecosystem. Free-living cyanobacteria produce 0.3 μg/g BMAA, but produce 2-37 μg/g as symbionts in the coralloid roots of cycad trees. BMAA is concentrated in the developing reproductive tissues of the cycad Cycas micronesica, averaging 9 μg/g in the fleshy seed sarcotesta and a mean of 1,161 μg/g BMAA in the outermost seed layer. Flying foxes (Pteropus mariannus), which forage on the seeds, accumulate a mean of 3,556 μg/g BMAA. Flying foxes are a prized food item of the indigenous Chamorro people who boil them in coconut cream and eat them whole. Chamorros who die of amyotrophic lateral sclerosis/parkinsonism-dementia complex (AL-SPDC), a neurodegenerative disease with symptoms similar to amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's disease, have an average of 6.6 μg/g BMAA in their brain tissues. The biomagnification of BMAA through the Guam ecosystem fits a classic triangle of increasing concentrations of toxic compounds up the food chain. This may explain why the incidence of ALS-PDC among the Chamorro was 50-100 times the incidence of amyotrophic lateral sclerosis elsewhere. Biomagnification of cyanobacterial BMAA may not be unique to Guam; our discovery of BMAA in the brain tissue from Alzheimer's patients from Canada suggests alternative ecological pathways for the bioaccumulation of BMAA in aquatic or terrestrial ecosystems.

Thidiazuron : A potent regulator of in vitro plant morphogenesis

Abstract: TDZ (N-phenyl-N’-1,2,3-thidiazol-5-ylurea) is a substituted phenylurea compound which was developed for mechanized harvesting of cotton bolls and has now emerged as a highly efficacious bioregulant of morphogenesis in the tissue culture of many plant species. Application of TDZ induces a diverse array of cultural responses ranging from induction of callus to formation of somatic embryos. TDZ exhibits the unique property of mimicking both auxin and cytokinin effects on growth and differentiation of cultured explants, although structurally it is different from either auxins or purine-based cytokinins. A number of physiological and biochemical events in cells are likely to be influenced by TDZ, but these may or may not be directly related to the induction of morphogenic responses, and hence, the mode of action of TDZ is unknown. However, the recent approaches applied to study the morphogenic events initiated by TDZ are clearly beginning to reveal the details of a variety of underlying mechanisms. Various reports indicate that TDZ may act through modulation of the endogenous plant growth regulators, either directly or as a result of induced stress. The other possibilities include the modification in cell membranes, energy levels, nutrient uptake, or nutrient assimilation. In this review, several of these possiblities are presented and discussed in light of recently published studies on characterization of TDZ-induced morphogenic effects.

A mechanism for slow release of biomagnified cyanobacterial neurotoxins and neurodegenerative disease in Guam

Abstract: As root symbionts of cycad trees, cyanobacteria of the genus Nostoc produce beta-methylamino-l-alanine (BMAA), a neurotoxic nonprotein amino acid. The biomagnification of BMAA through the Guam ecosystem fits a classic triangle of increasing concentrations of toxic compounds up the food chain. However, because BMAA is polar and nonlipophilic, a mechanism for its biomagnification through increasing trophic levels has been unclear. We report that BMAA occurs not only as a free amino acid in the Guam ecosystem but also can be released from a bound form by acid hydrolysis. After first removing free amino acids from tissue samples of various trophic levels (cyanobacteria, root symbioses, cycad seeds, cycad flour, flying foxes eaten by the Chamorro people, and brain tissues of Chamorros who died from amyotrophic lateral sclerosis/Parkinsonism dementia complex), we then hydrolyzed the remaining fraction and found BMAA concentrations increased 10- to 240-fold. This bound form of BMAA may function as an endogenous neurotoxic reservoir, accumulating and being transported between trophic levels and subsequently being released during digestion and protein metabolism. Within brain tissues, the endogenous neurotoxic reservoir can slowly release free BMAA, thereby causing incipient and recurrent neurological damage over years or even decades, which may explain the observed long latency period for neurological disease onset among the Chamorro people. The presence of BMAA in brain tissues from Canadian patients who died of Alzheimer's disease suggests that exposure to cyanobacterial neurotoxins occurs outside of Guam.

Occurrence of beta-methylamino-l-alanine (BMAA) in ALS/PDC patients from Guam.

Abstract: We tested the brain tissues of the Chamorro people of Guam who died of amyotrophic lateral sclerosis/Parkinsonism dimentia complex (ALS/PDC) for the neurotoxin beta-methylamino-l-alanine (BMAA). We used validated high-pressure liquid chromatography and liquid chromatography-mass spectrometry analyses to test well-characterized archival tissues of the superior frontal gyrus from eight Chamorros from Guam and a comparison group of 15 Canadians. BMAA was found as a free amino acid in 83% of Chamorro ALS/PDC patients (3-10 microg/g) as a protein-associated amino acid in 100% of the Chamorro individuals (149-1190 microg/g). Both forms of BMAA were also found at comparable levels in two Canadians who died of progressive neurodegenerative disease. BMAA, which is produced by cyanobacteria, may be associated with some cases of neurodegenerative disease.

Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products

Abstract: Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.

Eutrophication science: where do we go from here?

Abstract: Cultural eutrophication has become the primary water quality issue for most of the freshwater and coastal marine ecosystems in the world. However, despite extensive research during the past four to five decades, many key questions in eutrophication science remain unanswered. Much is yet to be understood concerning the interactions that can occur between nutrients and ecosystem stability: whether they are stable or not, alternate states pose important complexities for the management of aquatic resources. Evidence is also mounting rapidly that nutrients strongly influence the fate and effects of other non-nutrient contaminants, including pathogens. In addition, it will be important to resolve ongoing debates about the optimal design of nutrient loading controls as a water quality management strategy for estuarine and coastal marine ecosystems.

Influence of abiotic stress signals on secondary metabolites in plants

Abstract: Plant secondary metabolites are unique sources for pharmaceuticals, food additives, flavors, and industrially important biochemicals. Accumulation of such metabolites often occurs in plants subjected to stresses including various elicitors or signal molecules. Secondary metabolites play a major role in the adaptation of plants to the environment and in overcoming stress conditions. Environmental factors viz. temperature, humidity, light intensity, the supply of water, minerals, and CO2 influence the growth of a plant and secondary metabolite production. Drought, high salinity, and freezing temperatures are environmental conditions that cause adverse effects on the growth of plants and the productivity of crops. Plant cell culture technologies have been effective tools for both studying and producing plant secondary metabolites under in vitro conditions and for plant improvement. This brief review summarizes the influence of different abiotic factors include salt, drought, light, heavy metals, frost etc. o...

Climate change: A catalyst for global expansion of harmful cyanobacterial blooms

Abstract: Cyanobacteria are the Earth's oldest known oxygen-evolving photosynthetic microorganisms, and they have had major impacts on shaping our current atmosphere and biosphere. Their long evolutionary history has enabled cyanobacteria to develop survival strategies and persist as important primary producers during numerous geochemical and climatic changes that have taken place on Earth during the past 3.5 billion years. Today, some cyanobacterial species form massive surface growths or 'blooms' that produce toxins, cause oxygen depletion and alter food webs, posing a major threat to drinking and irrigation water supplies, fishing and recreational use of surface waters worldwide. These harmful cyanobacteria can take advantage of anthropogenically induced nutrient over-enrichment (eutrophication), and hydrologic modifications (water withdrawal, reservoir construction). Here, we review recent studies revealing that regional and global climatic change may benefit various species of harmful cyanobacteria by increasing their growth rates, dominance, persistence, geographic distributions and activity. Future climatic change scenarios predict rising temperatures, enhanced vertical stratification of aquatic ecosystems, and alterations in seasonal and interannual weather patterns (including droughts, storms, floods); these changes all favour harmful cyanobacterial blooms in eutrophic waters. Therefore, current mitigation and water management strategies, which are largely based on nutrient input and hydrologic controls, must also accommodate the environmental effects of global warming.