Part 1: The Phototrophic Bacteria

This page describes the purple phototrophic bacteria and the green sulfur phototrophic bacteria.
Located below are the keys to the families and the genera with links to each genus page.

Green plants and Cyanobacteria are not included in Part 1. Green plants and the Cyanobacteria (blue-green algae) have these traits:

The Order Rhodospirillales (Bergey Part 1) includes all the phototrophic bacteria. Some of these bacteria can grow in presence of air and some can't. These bacteria

The Order Rhodospirillales (Bergey Part 1) contains three families of Phototrophic Bacteria:

Key to the Families of the Order Rhodospirillales

I. Cells contain bacteriochlorophyll a or b located on specialized membranes continuous with cytoplasmic membrane.

    A. Cells not able to use elemental sulfur as electron donor ====> Family I Rhodospirillaceae

    B. Cells able to use sulfur and sulfide as the sole photosynthetic electron donor and sulfur can be oxidized to sulfate. =================================> Family II Chromatiaceae

II. Cells contain bacteriochlorophyll c or d and these are located in chlorobium vesicles which are attached to the cytoplasmic membrane. ===================> Family III Chlorobiaceae

Key Facts about the Phototrophic Bacteria

1. Photo growth occurs only in anaerobic condition for all three families: I, II, and III.

2. Family I can grow in dark on yeast, but grows better in light and has purple color only in light because the purple chlorophyll is needed only in light.

3. Families II and III grow only in light and require sulfur as electron donor.

4. Both II and III require sulfur, but II is purple and III is mostly green; one is brown.

5. Families I and II need purple chlorophyll because they grow in stagnant bottom muds where only purple is needed to trap the light that got thru the dense top algae.

6. The purple bacteria are mostly red to purple (orange and red, brown); but one species is green.

The Family Rhodospirillaceae (Purple; survives air)

Cells spherical to rod to vibrio to spiral shaped. Multiplication by fission or budding. Phytosysnthetic membrane system continuous with cytoplasmic membrane. No gas vacuoles in known genera. Usually microaerophilic, but some strains able to grow in air in light or dark. Red pigment decreased when grown in increaseing oxygen. TO BE continued.

Key to the Genera of the family Rhodospirillaceae

I. Cells spiral shaped ============================> Rhodospirillum   page 410a

II. Cells ovoid to rod shape; not forming filaments ======> Rhodopseudomonas  page 410b

III. Cells ovoid to enlongated ovoid, forming filaments == ==> Rhodomicrobium    page 410c

The Family Chromatiaceae (Purple)

Cells spherical, ovoid, rod, vibrio, or spiral shaped; motile or non-motile; with or without gas vacuoles. Motile forms have polar flagella and in the largest forms the tuft of polar flagella is visible by light microscope. Cells contain bacteriochlorophylls a or b, caroenoids of groups 1, 3, or 4, or tetrahydrospirilloxanthin. Internal phytosynthetic membrane continuous with cytoplasmic membrane.

Most species are strictly anaerobic--only Thiocapsa roseopersicina is able to grow in dark under microaerophilic conditions. Capable of photolithrotrophic CO2 assimilation in the presence of elemental sulfur and sulfide. Elemental sulfur (the ultimate oxidation product) accumulates as globules inside the cells (externally in Ectothiorhodospira). All strains are able to photoassimilate simple organic compounds such as acetate and pyruvate TO BE CONTINUED

Key to the Genera of the family Chromatiaceae

I. Sulfur globules stored inside he cells when grown with sulfide as electron donor.
  A. Cells do not contain gas vacuoles.
    1. Cells motile by polar flagella
        a. Cells Ovoid to rod shaped ====> Chromatium page 410d
        b. Cells Spherical; usually diplococcus shaped before cell division ====> Thiocystis 410e
        c. Cells sperical to ovoid, in sarcina packets =======> Thiosarcina 410f
        d. Cells spiral shaped =============> Thiospirillum 410g
    2. Cells non-motile
        a. Cells spherical, diplococcus shape before division,
            thick slime often surrounds individual clells =====> Thiocapsa 410h
  B. Cells contain gas vacuoles
    1. Cells motile by polar flagella
        a. Cells spherical, typically diplococcus before division ===> Lamprocystis 410i
    2. Cells non-motile
        a. Cells rod shaped ==========> Thiodictyon 410j
        b. Cells sperical and in flat sheets =======> Thiopedia 410k
        c. Cells spherical =============> Amoebobacter 410l
II. Sulfur globules appearing outside cells when S-- electron donor ===> Ectothiorhodospira m

The Family Chlorobiaceae (Green or Brown)

Cells spherical, ovoid or rod shape. Binary or binary and ternary fission. Cells non-motile except Genus Chloropseudomonas has polar flagella. In presence of sulfide, globules of sulfur deposited outside cells never inside. Single cells and cultures are green or brown. Photopigments located in chlorobium vesicles which underlie and attach to cytoplasmic membrane.

Bacteriochlorophylls c or d are main pigments. All forms strict anaerobes and obligately phototrophic. Capable of photolithotrophic assimilation of CO2 in presence of sulfide or sulfur which is oxidized to sulfate. TO BE CONTINUED

Key to the Genera of the family Chlorobiaceae

I. Cells free living and not intimately associated with other microbes.
  A. Cells do not contain gas vacuoles
    1. Cells not motile
        a. Cells ovoid to rod shape or vibrioid ======> Chlorobium
        b. Cells irregular spherical to starlike, covered with extrusions ====> Prosthecochloris
    2. Cells motile by means of polar flagella; rods ========> Chloropseudomonas
  B. Cells contain gas vacuoles; non-motile
    1. Cells rods to ovoid; may aggregate in specific patterns =====> Pelodictyon
    2. Cells coccus to ovoid; may aggregte in specific patterns =====> Clathrochloris
II. Cells in symbiotic aggregates with other microbes. These stable aggregates consist of a large colorless central bacterium surrounded by small green cells. Not to be further discussed at this time.


You may send private e-messages to Dr. Eddleman and he will reply, usually within 24 hours.
First installed February 1999      Revision #0 1999 Feb 22       indbio@disknet.com
Written by Harold Eddleman, Ph. D., President, Indiana Biolab, 14045 Huff St., Palmyra IN 47164
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