Individual bacteria of Thiodictyon are rod-shaped with rounded ends, sometimes needle-shaped. The study found that the bacteria reproduced by binary division and were immobile in all cases. Under natural conditions, Thiodictyon can form aggregates in which cells are arranged end-to-end in an irregular network. However, the shape is unstable, and the cells can form tighter clusters or break into individual cells. According to characteristic classification, Thiodictyon belongs to Gram-negative bacteria. Bacterial cells contain bacteriochlorophyll a and carotenoids, and these two pigments are located on the inner membrane of the cyst. There are air bubbles in the central part of the cells.
Figure 1. Phase-contrast photomicrograph of "T. syntrophicum" sp. nov. strain Cad16T. (Samuel M. Luedin, et al.; 2018)
Thiodictyon is an anaerobic bacteria. In the presence of hydrogen sulfide, the bacteria can perform photosynthesis, and can produce and store spherical elemental sulfur as an intermediate oxide in a bubble-free area in the cell. Molecular hydrogen can be used as an electron donor. Molecular oxygen is not released during photosynthesis. Due to the presence of photosynthetic pigments, the cell suspension appears purple to violet in color.
Thiodictyon contains two different types of species: one is that cells can form typical reticular aggregates-Thiodictyon elegans; the other is that cells cannot form reticular aggregates, usually in the form of free single cells-Thiodictyon bacillosum.
Thiodictyon elegans has a cell width of 1.5-2.0 μm and a cell length of 3.0-8 μm. Cells usually form aggregates in which they neatly form end-to-end in an irregular network, somewhat resembling the shape of the green algae Hydrodictyon. The aggregates are unstable in shape, and cells can form tight piles or break into individual cells. Single cells were gray, and cell suspensions were purple to violet.
Thiodictyon elegans is an obligate photoautotroph and is strictly anaerobic. The optimum growth pH range of the bacteria is: 6.5-7.6. Optimum growth temperature: 20℃. Photosynthetic electron donors are: sulfide or sulfur. Acetate and pyruvic acid can be photoassimilated in the presence of sulfide and bicarbonate. Under natural conditions, Thiodictyon elegans lives in exposed hydrogen sulfide-containing mud and stagnant water or hot springs.
Thiodictyon bacillosum has a cell length of 3-6 microns and a cell width of 1.5-2.0 microns. Cells can form irregular aggregates surrounded by mucus, not network aggregates. Individual cells are gray, and cell suspensions are purple-violet in color.
Thiodictyon bacillosum is an obligate photoautotroph, strictly anaerobic. Optimum growth pH range: 6.5 to 7.5. Optimum growth temperature: 20°-26°C. When photosynthesis occurs, the photosynthetic electron donor is sulfide or sulfur. In the presence of sulfide and bicarbonate, acetate and propionate can be photosynthesized, but sulfate cannot be assimilated. Under natural conditions, Thiodictyon bacillosum lives in exposed hydrogen sulfide-containing mud and stagnant water or hot springs.
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