Algae play a fundamental role in the biosphere as primary producers in the aquatic environment. Through their photosynthetic abilities, algae produce oxygen and take up carbon dioxide, and provide food and energy to other biota in their immediate surroundings. Humans have also been using various species of green, brown and red algae as food, due to the proteins, carbohydrates, minerals and vitamins, found in the cell wall or in the cytoplasm. These include Monostroma, Ulva, Codium and Chlorella. There are also other industrial uses of algae such as biofuel.

However, algal growth, if left unchecked, can also be harmful to humans and the environment. The most common problems are related to excessive total biomass which leads to depletion of dissolved oxygen, and the production of toxins, that in sufficient doses, can cause food poisoning, liver damage and even paralysis.

One particular aspect of some algae is their ability to emit objectionable tastes or odors, known as off-flavours. Above a certain threshold level, off-flavour compounds such as 2-methylisoborneol (2-MIB) and geosmin can be detected easily by humans. Researchers at the NUS Environmental Research Institute (NERI) have identified several local blue-green algal species (also known as cyanobacteria) in their study to understand the mechanisms of off-flavour production. Headed by Prof Karina Gin, the group has embarked on studies to better understand the dynamics of such blooms which produce these off-flavour compounds.

An array of methods ranging from genetic, chemical to metabolites analysis was developed using quantitative polymerase chain reaction (qPCR) and gas and liquid chromatography-mass spectrophotometry (GC-MS/LC-MS) for rapid detection of off-flavour levels and identification of the producers.

A 2-year study was conducted over 3 catchments in Singapore and revealed significant correlations with environmental factors especially temperature and nutrients. As Singapore has been experiencing warmer days as a result of global warming, cyanobacteria blooms have also been more rampant during the hot and dry seasons. In addition, to further understand the mechanisms of off-flavour production in cyanobacteria, three local species which were isolated from the reservoirs and positively identified as 2-MIB producers, were studied under laboratory controlled conditions to elucidate the effects of environmental factors such as temperature, light and nutrients on its production.

The studies have revealed a significant increase in growth of these species at high temperature (up to 38°C), light and phosphorus. Furthermore, higher phosphorus induces higher cellular production of 2-MIB. Overall, the studies have revealed the potential effect of global warming on the off-flavour production by cyanobacteria. This could pose challenges for drinking water treatment and affect the aesthetics of reservoirs used for recreational purposes.