The adaptation of chlamydiae to facultative host multicellularity

Area of Science:

• Microbiology
• Symbiosis
• Bacteriology

Background:

• Chlamydiota are obligate intracellular bacteria with a conserved biphasic developmental cycle (intra- and extracellular stages).
• Dictyostelium giganteum, a social amoeba, exhibits complex multicellular life cycle stages, including aggregation and spore formation.
• While amoebae associate with bacteria, chlamydial symbionts in these hosts are newly discovered.

Purpose of the Study:

• To characterize a novel chlamydial symbiont found in the social amoeba Dictyostelium giganteum.
• To investigate the developmental cycle and transmission mechanisms of this unique chlamydial symbiont.

Main Methods:

• Isolation and identification of the chlamydial symbiont.
• Fluorescence microscopy and quantitative PCR to track symbiont transmission.
• Transmission electron microscopy to examine symbiont morphology.
• Genomic analysis to identify genes related to developmental cycle and survival.

Main Results:

• A novel chlamydial species, Reclusachlamydia socialis, was identified and is retained throughout the host's life cycle.
• The symbiont lacks a detectable extracellular form, indicating a deviation from the typical chlamydial developmental cycle.
• Transmission relies exclusively on cell-to-cell contact during amoeba aggregation.
• Absence of essential genes for extracellular survival and developmental cycle regulation was confirmed.

Conclusions:

• Reclusachlamydia socialis represents a significant variation in the conserved chlamydial developmental cycle, highlighting bacterial adaptability.
• This discovery expands the understanding of endosymbiosis, particularly in the context of facultative host multicellularity.