Mollicutes

Bacteria that lack cell walls

Features

  • Lack cell walls around their cell membrane

    • Makes them resistant to many antibiotics which target cell wall synthesis

  • Very small (0.1-0.3 micrometers)

    • Smallest known cell in biology

  • Parasites of plants and animals; some are saprotrophic

  • Phytoplasma, Spiroplasma, and Mycoplasma are common mollicute plant pathogens

Phytoplasmas

    • Very small bacterial cells (less than 0.1 µm) with small genomes

    • Obligate parasites on plant phloem cells, affecting many important agriculture plants

    • A common symptom is "phyllody", or the creation of compacted leafy shoots in place of flowers, causing sterility.

Above: Phyllody in Echinacea purpurea

Above: Aster-yellows in carrots (and marigolds) caused by Candidatus phytoplasma asteris

Below: Prunus X-disease caused by Candidatus phytoplasma pruni

Left: Pear decline caused by Candidatus phytoplasma pyri

Right: Lethal yellowing of coconuts caused by Candidatus phytoplasma palmae

https://sites.google.com/site/botany317/session-2/bacteria/mycoplasmas/Cocos%20Lethal%20Yellowing.jpg?attredirects=0

Spiroplasmas

  • Spiral-shaped

  • Usually plant pathogens

  • Infect the phloem sieve elements

https://sites.google.com/site/botany317/session-2/bacteria/mycoplasmas/Citrus%20Stubborn%20Disease.jpg?attredirects=0
http://www.apsnet.org/publications/imageresources/PublishingImages/2000/spiroplasma.jpg

Above: Spiroplasmas in a phloem cells

Left: Citrus stubborn disease caused by Spiroplasma citri (on left)

Mycoplasmas

    • Very small bacterial cells (0.1 µm)

    • Can survive without oxygen

Additional Resources