Plant Biology: Bacteria, Archaea, and Viruses

Introduction

Fossils of bacteria have been found up to 3.5 billion years old

The first eukaryotic cells are 2.7 billion years old

There are approximately 2 billion species of bacteria on Earth and more than 90% are either harmless or useful to humans

Domains and Kingdoms Bacteria and Archaea

All have prokaryotic cells

  • No nuclear envelopes
  • Circular DNA strands
  • No membrane-bound organelles

Cells may be colonial or filamentous, but each cell is independent

Riosomes and plasmids (small circular DNA molecules, useful for genetic engineering) are present

Nutrition is primarily acquired by absorption of food through the cell wall, though some can photosynthesize

Reproduction occurs asexually through fission, not mitosis

Classification of Bacteria

Most bacteria are tiny

Occur primarily in three forms:

  1. Cocci - spherical or elliptical shaped bacteria
  2. Bacilli - rod-shaped or cylindrical shaped bacteria
  3. Spirilla - helix or spiral shaped bacteria

Gram stains can also be used to categorize bacteria - gram-negative or gram-positive based on dye in cell walls

Phylum Bacteriophyta

Can be heterotrophic

  • Saprobes obtain food from nonliving organic matter
  • Parasites depend on living organisms for food

Can also be autotrophic

Can also be chemotrophs

  • Chemotrophs obtain energy from various compounds or elements such as iron, sulfur, and hydrogen bacteria

Disease Bacteria

Spread is possible through air, food, direct contact with skin or mucus membranes, wounds, and bites of insects and other organisms

Koch’s Postulates

Koch’s Postulates are rules for proving a particular microorganism is the cause of a particular disease

  1. Microorganism must be present in all cases of disease
  2. Microorganism must be isolated in pure culture
  3. Microorganisms from pure culture must be able to infect hosts
  4. Microorganisms must be isolated from experimentally-infected host and grown in pure culture for comparison with the original culture

Bacteria can be useful, for example in making cheese and buttermilk, various industrial uses, and biocontrol

Class Cyanobacteria

Cyanobacteria have chlorophyll a and oxygen is produced from photosynthesis

It is believed that chloroplasts originated as Cyanobacteria

Domain and Kingdom Archaea

Metabolism is fundamentally different from bacteria

Three distinct groups

  1. Methane bacteria - killed in the presence of oxygen
  2. Salt bacteria - thrive in extreme salinity
  3. Sulfolobus bacteria - survive temperatures up to 170 degrees Fahrenheit

Viruses

Lack cytoplasm or any cell structure

Don’t grow or divide, don’t respond to external stimuli

Unclear if they are actually alive, but they probably aren’t

In a living cell, viruses express their genes and use cellular machinery to produce more virus particles

Viruses consist of a nucleic acid core surrounded by a protein coat

A virus core consists of DNA or RNA but not both

Viroids - circular strands of RNA that occur in nuclei of infected plant cells

Prions - particles of protein that cause diseases of animals and humans that are believed to cause disease by inducing abnormal protein folding in the brain resulting in brain damage