Waste
and WaterWaste
and Water
Some bacteria do not only have the capacity to test water, a few types may make it safer for us to drink as well. One way in which this may be done is by way of removing poisonous chemicals.
Almost any chemical can be broken down by bacteria into less harmful products. Bacteria are amazingly adaptable and if a chemical is put into an environment, a species of bacteria may quickly appear that is able to live there – most often by breaking down the toxin and so making it a safer place to live.
A good example of this is in a group of bacteria that break down chemicals called PCBs. These chemicals were used in dozens of industries before being banned for being highly toxic and seemingly indestructible by bacteria, fungi or other natural means. It is thought that 18,000 seal deaths in the late 1980s can be attributed to this cause.
Bacteria reproduce at an extremely fast rate and some may double population size every 20 minutes under ideal conditions (this is in the lab – it may be anything from hours to months in the wild).
What this means is that mutants occur relatively often compared to animals (eg humans) that do not reproduce as quickly. The human population of earth is currently 6 billion – apparently clear water may have this many bacteria in an area the size of a 1 cm cube.
Mutations are inheritable changes – this means they are passed on to offspring. Most mutations are bad or neutral and the bacteria with these mutations do not perform as well as the ‘normal ones’ and are eliminated according to Darwin’s ‘survival of the fittest’. Some mutations, however, are useful and help the bacteria in some way – these ones survive better than the ‘normal’ ones and so reproduce at their expense.
This means that if tiny amounts of a chemical are put into a population of bacteria, eventually a mutant will appear that can break down that chemical. This bacterium will have an advantage over its neighbours and so will increase rapidly in numbers.
It should be emphasised that mutation is a rare event and useful mutation is even rarer. In the case of PCBs, the chemicals are so difficult to degrade that the successful mutation only appeared in one place in the world – the contaminated Hudson River in the USA.
What the bacterium does for its own comfort may be turned to our advantage. Industrial chemicals of all natures have at one time or another found their way into the water supply and by employing bacteria to degrade these, we may make these areas safe again. The same techniques may be employed to make useable land from areas contaminated by dangerous pesticides or chemical spills.
Another type of bacteria can degrade relatives of the CFCs (HFCs and HCFCs) that are thought to be responsible for much of the damage to the ozone layer. These varied examples give hope that whatever messes we may have made of our planet in the past, bacteria can help us clean up.
Another way in which bacteria safeguard our water is by way of bacteriocins – these are poisons released by some bacteria, which kill other types. They are similar to antibiotics but are much more specific. This means that they only kill certain types of bacteria and that they have little or no effect on animals or people.
Some researchers have found it possible to isolate bacteria that produce bacteriocins (from wells in Chile) against the bacteria most likely to cause human disease. This means that these ‘friendly’ bacteria will destroy, or greatly reduce the numbers of, the others.
Even more important is the fact that the genes responsible for bacteriocins are known - genetically engineered bacteria could be made that would release these toxins against many (or possibly all) dangerous bacteria rather than just one or two as in the wild.