Miscellany

	Reintroduction: setting the ball rolling...
	Valuing Nature ?
	Two short notes on statistics
	Biomonitoring ecotoxicity of heavy metal using a new bacterium
	Cyanbacteria culture collection: a unique resource for ecology and biotechnology research

Biomonitoring ecotoxicity of heavy metal using a new bacterium

Owing to the rapid growth of the global human population coupled with an increase in living standards, various of the agricultural and industrial pollutants generated each year have increased significantly since the industrial revolution. As a result, pollution has become a major concern as it adversely affects the well-being of natural flora and fauna, and impairs ecosystem balance. A proper monitoring system is the first-step to safeguard our environment because precise information on the source, place and severity of pollution is essential for us to design and implement conservation programmes, or to decide what remedial measure(s) has(have) to be carried out.

Conventional chemical analyses give information that has very little relevance to the ecological impact of pollutants. Chemical methods provide information on the quantity of pollutants in samples from a specific environment, while biomonitoring attempts to establish the relationship between the presence of a pollutant at a certain concentration and the negative effect(s) it exerts on living organisms. Ecological monitoring has been given increasing attention because of the potential establishment of a correlation between the chemical nature of the pollutant and its biological effects. Organisms including plants, animals, protozoa and microorganisms have been adopted in biomonitoring programmes. There is not much difference between using ‘macro-organisms’ and microorganisms, and the majority of bioassays are based on presence-absence (P-A) or on physiological, behavioural or genotypic expression of certain (or groups of) indicator organisms. For instance, Astragalus spp. are regarded as selenium (Se, a highly toxic metalloid) indicator plants because they are exceptionally resistant to, and have ability to accumulate high levels of selenium, while most other living organisms will die even under very low concentrations of selenium. Thus the presence of Astragalus spp. implies that the area is selenium-laden (Rosenfeld & Beath, 1964). Similarly, coliform, which is a group of rod-shape bacteria, is another well-known bioindicator for pollution where the abundance of coliform bacteria (common species like Escherichia coli) indicates the extent of faecal contamination. In addition, a number of commercially available toxicity testing kits, like the Microtox^® test, are making use of the altered physiological and biochemical responses of bacteria (like Vibrio fischeri) under stressful environmental conditions to reflect the severity of pollution level.

Recently, a bacterium (Vogesella indigofera, Fig. 1) was isolated from a drinking water filter cartridge containing activated-carbon, and found to respond to heavy metal quantitatively (Gu & Cheung, 2001). Under conditions without pollution by metals, this bacterium produces a blue pigmentation, whether in liquid culture (Fig. 2) or as colonies on an agar plate, so distinctive that any morphological change might easily be detected visually and assessed. In the presence of hexavalent chromium (Cr⁶⁺, a toxic and carcinogenic heavy metal), their pigment production will be obstructed, and the relationship between chromium concentrations (both in liquid culture and on agar plate) and blue-pigment production by the bacterium are negatively correlated (r² = -0.877). By comparing against standards the intensity of the blue-colour of the liquid culture or percentage of blue colonies growing on an agar plate, the concentration of chromium in samples suspected to be contaminated with chromium can be estimated. The philosophy for this test is actually similar to the Microtox^® test which measures the intensity of light emitted by the bioluminescent bacteria with a photometer; instead, intensity of blue-colour is being assessed here with less sophisticated instruments and without tedious procedures required. It is an easy, simple and cost-effective way to monitor chromium with this bacterium, and the feasibility of using this bacterium to quantify other heavy metals is worth investigating in the future.

Bibliography

Gu, J.D. & Cheung, K.H. (2001). Phenotypic expression of Vogesella indigofera upon exposure to hexavalent chromium, Cr⁶⁺. World J. Microbiol. Biotechnol. 17: 475-480.

Rosenfeld, I. & Beath, O.A. (1964). Selenium: Geobotany, Biochemistry, Toxicity, and Nutrition. Academic Press Inc., New York.

Fig. 1. A scanning electron micrograph of V. indigofera (Bar = 1 m m).	Fig. 2. Liquid culture of V. indigofera. The dark blue culture (for left) was the control without Cr6+, while the light yellow one (for right) was amended with 100 ppm Cr6+.