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Chlamydiae represent a diverse group of obligate intracellular bacteria with elusive hosts in environmental settings. This study used one of the largest collections of wild amoebae (Dictyostelium discoideum and D. giganteum, 106 clones) collected over the past two decades to screen for novel environmental chlamydiae. We found that novel environmental chlamydiae are prevalent in two wild Dictyostelium species and assembled 42 novel chlamydiae metagenome-assembled genomes (MAGs). The MAGs represent three chlamydiae species previously only reported using 16S sequencing. Their genomes are divergent enough from other species to warrant placing them in two new genera (tentatively called Ca. Dictychlamydia sp. LF1, Ca. Dictychlamydia sp. LF2, and Ca. Feichlamydia sp. LF3). In addition, these chlamydiae species show strong host specificity with two Dictyostelium amoeba hosts, except one amoeba sample. Ca. Dictychlamydia sp. LF1 and Ca. Feichlamydia sp. LF3 was exclusively observed in D. discoideum, while Ca. Dictychlamydia sp. LF2 was found only in D. giganteum. Phylogenetic and comparative genomic analyses suggest that all three chlamydiae are close to arthropod-associated chlamydiae and likely have some intermediate characteristics between previously reported amoeba-associated and vertebrate-associated chlamydiae. This study significantly broadens our understanding of the chlamydial host range and underscores the role of amoebae as vital hosts for environmental chlamydiae.
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A unified model for the dynamics of ATP-independent ultrafast contraction
In nature, several ciliated protists possess the remarkable ability to execute ultrafast motions using protein assemblies called myonemes, which contract in response to Ca 2+ ions. Existing theories, such as actomyosin contractility and macroscopic biomechanical latches, do not adequately describe these systems, necessitating development of models to understand their mechanisms. In this study, we image and quantitatively analyze the contractile kinematics observed in two ciliated protists ( Vorticella sp. and Spirostomum sp.), and, based on the mechanochemistry of these organisms, we propose a minimal mathematical model that reproduces our observations as well as those published previously. Analyzing the model reveals three distinct dynamic regimes, differentiated by the rate of chemical driving and the importance of inertia. We characterize their unique scaling behaviors and kinematic signatures. Besides providing insights into Ca 2+ -powered myoneme contraction in protists, our work may also inform the rational design of ultrafast bioengineered systems such as active synthetic cells.
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- PAR ID:
- 10426752
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 120
- Issue:
- 25
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2217737120
