Biomarker Development Group
A biomarker is defined as “a biological response to an environmental perturbation”. Environments change naturally on several timescales, ranging from diurnal to geological cycles. On top of this layer of change are the (relatively) short-term anthropogenic changes to environments.
Organisms are constantly forced to adapt to these changes, either by moving away, thus changing their biogeographical range, or adapting to the changed environment. In the event that movement is not an option (e.g. sessile organisms, or the inability of the food source to move) adaptation is required to ensure survival. The adaptive response is energetically expensive and we find a redistribution of the organism’s energy reserves toward the stress response and away from growth and resproductive investment.
The latter effect, though sublethal, may be detrimental to the survival of populations and consequently the functioning of ecosystems.
Adaptation to stress
Adaptation can occur on several levels of biological organization. A response seen at the level of the organism, e.g. behaviour or metabolic rate, ispreceded by an intricate complex of structural, physiological, chemical and biochemical responses that are triggered by cellular signalling processes. Consequently, we attempt to elucidate the stress response at the metabolomic, transcriptomic and proteomic level.
The aim of this approach is to identify reliable biomarkers that respond to stress in general, and to specific stressors (e.g. metals, ROS), in order to identify stressors before effects on whole animal physiology, health, fitness or survival manifests.
Naturally, the adaptive response is closely linked to the evolutionary history of the species and the range of environmental conditions where this drama unfolded. Here the comparative approach, as eloquently pursued by the great Knut Schmidt-Nielsen and his contemporaries, is of great value. Comparisons of species from the same environment with differential ranges of adaptability provide insight into the mechanistic functioning of the adaptive response.
The biomarker approach in our research
The biomarker approach as applied in our labs is aimed at identifying stress in organisms before fitness and survival are affected and before population level changes occur.
The biomarker approach can provide insight into the stress that animals experience in response to anthropogenic environmental change. Some general biomarkers, e.g. metabolic rate or heart rate, indicate that animals are stressed, without allowing elucidation of the cause. Some biomarkers respond to classes of pollutants like metals (e.g. metallothionein mRNA or protein), organic pollutants (e.g. CYP450, ARNT) or pesticides (acetylcholine esterase inhibition). The upregulation of some biomarkers are specific enough to indicate specific pollutants like lead (ALAD, delta-aminolevulinic acid dehydratase). We have been interested in metal pollution generally, but we have an affinity for copper specifically. The dilemma is that copper is an essential metal (animals are stressed by insufficient copper in their environment), that becomes toxic at elevated levels. Even though animals have very specific pathways to detoxify copper, the capacity of these pathways can be exceeded at high environmental copper levels, leading to copper exerting its toxic effect on biological systems. We have published on copper effects on crabs (two spp), fish (3 spp) and have recently taken to the air to assess metal insult on bats, in collaboration with Corrie Schoeman and his group.
We also apply the biomarker approach to assist the abalone mariculture industry in assessing and monitoring production animals for their level of stress. In this economically important industry it is of biological and financial importance to keep stress levels in animals as low as possible, as the stress response will channel energy away from growth and, consequently, profit. The challenge is to firstly understand “normal” abalone physiology, before deviations from the “norm” can be used as potential biomarkers. In this sense our work corresponds to translational medical research, where the aim is to develop new biomarkers that can be used to diagnose specific conditions.
Biomarkers of copper exposure in freshwater crabs and fish
Biomarkers of metal exposure in situ – the lab to field link
Water loss in abalone during simulated live export
Environmental drivers of ulcer formation in SA abalone
Thermal plasticity in winter acclimated SA abalone
Oxygen as limiting factor in abalone mariculture systems
Differential responses to oxygen stress in juvenile and adult abalone (ongoing project)
Environmentally induced changes in gene expression in SA abalone (ongoing project)
This overarching theme consists of several sub-projects, including:
– heat shock proteins
– genes regulating mitochondrial function
Biomarkers of copper exposure in brown mussels along the UKZN coast (ongoing project)
Biomarkers of metal toxicity in bats that utilize polluted urban rivers (ongoing project)
Thermal stress indicators in farmed SA abalone (ongoing project)
Vosloo, A, Van Aardt, WJ & Mienie, LJ (2002) Sublethal effects of copper on the freshwater crab Potamonautes warreni. Comparative Biochemistry and Physiology Part A, 133, 695–702. (doi:10.1016/S1095-6433(02)00214-3)
De La Rey, PA, Taylor, JC, Laas, A, Van Rensburg, L & Vosloo, A. (2004) Determining the possible application value of diatoms as indicators of general water quality: a comparison with SASS 5. Water SA. Vol 30 (3): 325-332.
Van Heerden, D, Vosloo, A & Nikinmaa, M. (2004) Effects of short-term copper exposure on gill structure, metallothionein and hypoxia inducible factor-1a (HIF-1a) in rainbow trout (Oncorhynchus mykiss). Aquatic Toxicology 69:271-280. (doi:10.1016/j.aquatox.2004.06.002)
Van Heerden, D, Tiedt, L & Vosloo, A. (2004) Gill damage in Oreochromis mossambicus and Tilapia sparrmanii after short term copper exposure. International Congress Series 1275: p 195 – 200. Collected papers from the 3rd ICCPB in Africa. Editors S Morris and A Vosloo. (doi:10.1016/j.ics.2004.08.071)
Thawley, SK, Morris, S & Vosloo, A. (2004) Zn and Cd accumulation in Potamonautes warreni from sites in the North-West Province of South Africa. International Congress Series 1275: 180 – 188. Collected papers from the 3rd ICCPB in Africa. Editors S Morris and A Vosloo. (doi:10.1016/j.ics.2004.09.036)
Morris, S & Vosloo, A. 2006. Animals and environments: Resisting schisms in comparative physiology and biochemistry. Physiological and Biochemical Zoology 79(2): 211 – 223. (DOI: 10.1086/499997)
Van Heerden, D, Jansen Van Rensburg, PJ, Nikinmaa, M & Vosloo, A. 2006. Gill damage, metallothionein gene expression and metal accumulation in Tilapia sparrmanii from selected field sites in Rustenburg and Potchefstroom, South Africa. African Journal of Aquatic Science 31(1): 89-98.
Vosloo, A & Vosloo, D. Routes of water loss in South African abalone (Haliotis midae) during aerial exposure. Aquaculture 261(2): 670-677. (doi:10.1016/j.aquaculture.2006.06.015)
Taylor, JC, Prygiel J., Vosloo, A, de la Rey PA and van Rensburg L. 2007. Can diatom-based pollution indices be used for bio-monitoring in South Africa? A case study of the Crocodile West and Marico water management area. Hydrobiologia, 592: 455-464. (doi:10.1007/s10750-007-0788-1)
PA de la Rey, H Roux, L van Rensburg and A Vosloo. 2008. On the use of diatom-based biological monitoring. Part 1: A comparison of the response of diversity and aut-ecological diatom indices to water quality variables in the Marico-Molopo River catchment. Water SA 34(1): 53-60.
PA de la Rey, L van Rensburg and A Vosloo. 2008. On the use of diatom-based biological monitoring Part 2: A comparison of the response of SASS 5 and diatom indices to water quality and habitat variation Water SA 34(1): 61-70.
Vosloo, D, du Preez, A, Pretorius, PJ & Vosloo, A. 2008. Both increased and diminished oxygen levels cause DNA damage in the haemocytes of cultured South African abalone (Haliotis midae). 4th CPB Meeting in Africa: Mara 2008. “Molecules to migration: The pressures of life” (Ed S. Morris & A. Vosloo). Medimond Publishing Co, Bologna, Italy. Pages 259 – 274.
Laas, A. & Vosloo, A. 2010. Exploring basic biochemical constituents in the body tissues of South African abalone Haliotis midae reared in shore-based mariculture systems. African Journal of Marine Science 2010. 32(1): 55-63.
Vosloo, D & Vosloo, A. 2010. Response of cold-acclimated, farmed South African abalone (Haliotis midae) to short-term and long-term changes in temperature. Journal of Thermal Biology 35(7): 317-323, DOI: 10.1016/j.jtherbio.2010.06.006.
Vosloo, A. 2010. Molecules to Migration: Pressures of Life. Physiological and Biochemical Zoology 83(5): 702-704.
Vosloo, D, Sara, J & Vosloo, A. 2011. Acute responses of brown mussel (Perna perna) exposed to sub-lethal copper levels: Integration of physiological and cellular biomarkers. Aquatic Toxicology 106/7: 1-8. doi:10.1016/j.aquatox.2011.10.001