Characteristics and Classification of Eukaryotic Microorganisms

General Characteristics of Eukaryotic Microorganisms

Overview of Eukaryotic Microorganisms

Eukaryotic microorganisms are a diverse group that includes several major types relevant to microbiology. These organisms are distinguished from prokaryotes by the presence of a true nucleus and membrane-bound organelles.

• Protozoa

• Fungi

• Algae

• Slime molds

• Water molds

These groups include both human pathogens and organisms essential for human life, such as those involved in nutrient cycling and food production.

Reproduction of Eukaryotes

Reproduction in eukaryotes is more complex than in prokaryotes, involving both asexual and sexual processes.

• DNA Organization: Most eukaryotic DNA is packaged as chromosomes within a nucleus.

• Asexual Reproduction: Eukaryotes have a variety of methods, including mitosis, budding, and binary fission.

• Sexual Reproduction: Many eukaryotes reproduce sexually by forming gametes and zygotes.

• Dual Modes: Algae, fungi, and some protozoa can reproduce both sexually and asexually.

• Multicellular Eukaryotes: Typically reproduce sexually.

Nuclear Division in Eukaryotes

The nucleus of eukaryotic cells may contain one or two complete copies of the genome, which determines their ploidy.

• Haploid (n): Single copy of the genome. Found in most fungi, many algae, and some protozoa.

• Diploid (2n): Two copies of the genome. Found in plants, animals, fungi, algae, and some protozoa.

Key Terms: Haploid refers to one set of chromosomes; diploid refers to two sets.

Classification of Eukaryotic Organisms

Taxonomy of eukaryotes has evolved from structural to molecular approaches.

• Early Classification: Based on structural similarities (morphology).

• Modern Classification: Relies on similarities in nucleotide sequences (molecular phylogeny).

Example: The classification of protists has changed significantly as genetic data has become available.

Protozoa

Defining Characteristics

Protozoa are a diverse group of unicellular eukaryotes that lack a cell wall and are typically motile.

• Eukaryotic

• Unicellular

• Lack a cell wall

• Motility: Move by cilia, flagella, and/or pseudopods

Distribution of Protozoa

Protozoa require moist environments and are found in a variety of habitats.

• Most live in ponds, streams, lakes, and oceans, where they are critical members of plankton.

• Others inhabit moist soil, beach sand, and decaying organic matter.

• Very few protozoa are pathogenic to humans.

Morphology of Protozoa

Protozoa exhibit great morphological diversity, including variations in nuclear structure and life cycle stages.

• Some have two nuclei:

  • Macronucleus: Contains many copies of the genome and controls cellular activities.

  • Micronucleus: Involved in genetic recombination and reproduction.

• Variety in number and types of mitochondria.

• Life cycle stages:

  • Trophozoite: Motile feeding stage.

  • Cyst: Resting, often resistant stage.

Nutrition of Protozoa

Most protozoa are chemoheterotrophic, obtaining nutrients by ingesting other organisms or organic matter.

• Phagocytize bacteria, decaying organic matter, other protozoa, or host tissues.

• Few absorb nutrients directly from surrounding water.

• Some, such as dinoflagellates and euglenoids, are photoautotrophic and can perform photosynthesis.

Key Terms: Chemoheterotrophs obtain energy and carbon from organic compounds; photoautotrophs use light as an energy source and CO2 as a carbon source.

*Additional info: Further details on protozoan classification, reproduction, and examples of human pathogens are typically included in a full chapter but were not present in the provided slides.*