Bacteria are single-celled organisms. They are prokaryotes and therefore do not have any cell organelles including a cell nucleus. They are believed to be one of the earliest type of life form that existed on Earth.

There are approximately 5 nonillion (5x1030 or 5 000 000 000 000 000 000 000 000 000 000!) bacteria on earth, with approximately 40 million bacteria in a single gram of soil.

Bacteria have a wide range of shapes including spheres, rods and spirals. Bacteria also have a wide range of habitats including those where no other life can exist, such as habitats with very high temperatures, very low temperatures and highly acidic conditions.

Bacteria reproduce asexually, with each bacterial cell growing to a fixed size before splitting into two identical daughter cells. Some bacteria form spores, but unlike fungi spores, these are protective rather than reproductive spores. Bacterial spores, such as anthrax spores, form in order to enable the bacteria to spread further and to survive conditions that would prevent growth. These spores are resistant to high temperatures, cleaning agents, ammonia and alcohol, and they are capable of surviving for hundreds of years.

Nature of science

Science is constantly changing as we learn more about the world around us. The development of new techniques, such as molecular biology techniques, can enable us to study things we haven’t been able to study before and to change the established view that we have.

Bacteria can get their energy from different sources – some from sunlight, some form organic compounds and some from inorganic compounds such as iron, sulphur and ammonia. Unlike higher order organisms, many bacteria are capable of growing without oxygen, and some bacteria even find oxygen toxic.

Bacteria can be divided into 24 phyla that are as different from each other as humans are to carrots! Bacteria were originally divided into these groups based on their appearance and cell metabolism but, with molecular biology techniques being able to compare the bacterial families at DNA level, many of these groupings might change as we realise that, though some bacteria may look similar, they aren’t, in fact, related at all. Molecular biology techniques that allow us to amplify DNA material from very small amounts have also enabled us to identify and characterise bacterial species that we aren’t able to culture in a laboratory.

Published 9 November 2008