The Molecules of Bacteria and Their Roles in Life

Bacteria are single-celled microorganisms built from chemical components known as molecules. While seemingly simple, the immense diversity of bacteria is mirrored by the complexity of the molecules they contain. These molecules are the machinery that drives all of a bacterium’s life processes, from energy production to reproduction. Understanding them provides insight into how bacteria survive and interact with their surroundings.

Essential Molecules Inside Bacteria

A bacterium’s life is supported by four major classes of macromolecules. The first are nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). A bacterium’s DNA is a single, circular chromosome in a region called the nucleoid that holds all genetic instructions. RNA molecules translate these instructions, with messenger RNA (mRNA) carrying the code, transfer RNA (tRNA) bringing amino acids, and ribosomal RNA (rRNA) being a component of ribosomes.

Proteins are another class of macromolecules that perform a vast range of functions. Many act as enzymes, speeding up the chemical reactions for metabolism. Other proteins provide structural support for features like flagella for movement or pili for attachment. Transport proteins are embedded in the cell membrane, controlling the passage of substances.

Lipids are a third class of molecules, best known for forming the cell’s boundary. The bacterial cell membrane is a phospholipid bilayer, creating a stable barrier between the cell and its environment. Lastly, carbohydrates, as polysaccharides, serve as energy reserves and structural materials. Some bacteria store energy in glycogen granules or use polysaccharides for protective outer layers.

A unique molecule found in most bacteria is peptidoglycan. This polymer of sugars and amino acids forms the rigid cell wall that surrounds the bacterial membrane. Peptidoglycan gives the cell its shape and protects it from bursting due to internal water pressure. Its structure is a common target for antibiotics, which disrupt its synthesis and compromise the cell’s integrity.

Molecules Bacteria Use to Engage Their World

Bacteria have a molecular toolkit for interacting with their environment. One way is through quorum sensing, a form of chemical communication. Bacteria release signaling molecules, and as the population grows, the concentration of these molecules increases. This allows bacteria to sense their population density and coordinate behaviors like forming biofilms or producing virulence factors.

To manipulate their surroundings, bacteria deploy effector molecules and toxins. These are often proteins secreted into a host cell or the environment. Exotoxins are released by living bacteria and have specific effects, while endotoxins are structural components of the outer membrane, like lipopolysaccharide (LPS), released when the bacteria die.

Many bacteria obtain nutrients by secreting extracellular enzymes. These proteins break down large molecules in the environment, such as cellulose or proteins, into smaller units that can be absorbed. This strategy is common for decomposer bacteria that recycle nutrients.

Iron is a necessary nutrient for bacteria but is often in short supply. To overcome this, many bacteria produce siderophores, small molecules with a high affinity for iron. These molecules are released to bind with available iron and transport it back to the bacterial cell.

Some bacteria also produce their own antibiotics. These molecules are used as chemical weapons to inhibit the growth of or kill competing microorganisms. This production gives these bacteria a competitive advantage in crowded microbial communities.

The formation of biofilms, communities of bacteria attached to a surface, is mediated by exopolysaccharides (EPS). These molecules form a slimy matrix that encases the bacteria. This matrix protects them from threats and helps them adhere to surfaces.

The Impact of Bacterial Molecules

The molecules produced by bacteria have far-reaching effects on health, industry, and the environment. In disease, molecules like toxins and extracellular enzymes are directly responsible for the symptoms of many bacterial infections. Biofilm formation can make infections difficult to treat, as the matrix protects bacteria from antibiotics and the host immune system.

Many bacterial molecules are beneficial to human health. Bacteria in the human gut, for example, produce useful molecules. They synthesize vitamins that humans cannot produce and break down complex carbohydrates into short-chain fatty acids, which are an energy source for colon cells. Some probiotic bacteria also produce antimicrobial peptides to defend against pathogens.

Biotechnology has harnessed bacterial molecules for numerous applications, including:

• Enzymes from bacteria in extreme environments, like Taq polymerase, which is used in the polymerase chain reaction (PCR).
• Antibiotics used in medicine, many of which were originally discovered in soil bacteria.
• The creation of bioplastics as a more sustainable alternative to conventional plastics.
• The development of biopesticides for agricultural use.

Bacterial molecules are also important to the functioning of ecosystems. The process of nitrogen fixation, which converts atmospheric nitrogen into a form usable by plants, is carried out by bacteria using specific enzymes. Decomposer bacteria use their extracellular enzymes to break down dead organic matter, recycling nutrients. Some bacteria can also produce molecules that break down pollutants, a process known as bioremediation.