• Introduction
• EVOLUTION
• Introduction
• The Theory
• Evidence
• DIVERSITY
• Bacteria
• Fungi
• Protists
• Viruses
• Size
• NUTRITION
• Introduction
• Autotrophy
• Heterotrophy
• REPRODUCTION
• Introduction
• Bacteria
• Fungi
• COMPETITION
• Evidence
• Mechanisms
• 
  
• LINKS
• VLE
• Bio Sciences
• Uni of Sydney

Diversity: Bacteria

Cells may be simplely structured (Eubacteria and Archaea, often called Prokaryote) or complex (Eukaryote)

Read the notes in the text, and below, and then use the following Drag and Drop exercise to test your in depth knowledge of the differences between Prokaryotes and Eukaryotes.

Drag & Drop Exercise

In our studies, we generally refer to all Prokaryotes as BACTERIA. However, Eubacteria genetically differ from Archaebacteria by more than from the Eukaryotes.

Structure

Prokaryotes consist of cells that lack membrane bound organelles. The organelles float within the cytoplasm. The nucleus also differs. In Prokaryotes, the nuclear region is a circular strand of DNA, that also floats in the cytoplasm. The wall, when present, may have a complex constitution (see figure on gram positive and gram negative). However, of most importance is that in Eubacteria, the wall may contain muriens (polysaccharide containing amide links), a compound not found in walls of Eukaryotic cells. The cell may also contain small loops of nucleic acid. Some of these may function independently of the cell, and they are called plasmids.

Most Bacteria exist as single cells, though some (Actinomyces) form filaments. The cells are always very simple and may be round (cocci), elongate (bacilli) or spiral (spirilli). The single cells of one type may aggregate in specific and predictable ways when grown on agar (e.g. Streptococcus and Staphlococcus).

Bacteria in Nature

In nature, bacteria tend to be found in complex communities, aggregating with other microbes. The communities probably form following the effects of quorum sensing, a signaling process that triggers aggregating behaviours on agar. These communities tend to be located in polysaccharide matrices called biofilm. Biofilm enables individuals to be in close contact and communication with cooperating microbes. The matrix enables movement of nutrients, signals and gas exchange while maintaining a moist habitat. Communities have been examined in the mouth associated with teeth, on surfaces in water, and even in water pipes. In fact microbial communities in biofilm are extremely common.

Size

Bacteria are very small. The smallest cells are around 0.35µm maximum diameter. These appear to be obligate parasites on and in other cells. For instance, the bdellovibrio are parasitic in other Eubacteria. The largest common bacteria are around 2µm long. These cells are usually capable of independent respiration, and can complete their life cycle without the support of other cells. to nutrition.

Importance

Bacteria are important for:

• fixing energy into organic forms,
• digestion of organic matter (see also fungi), to heterotrophy.
• fixing dinitrogen to a biologically useful form, and cycling of N in the biosphere
• industrial production (e.g. antibiotics, genetic engineering), to competition.
• food preservation and spoilage,
• diseases in all organisms as well as biological control of pests, weeds and pathogens,
• recycling of major minerals in the biosphere.