3D structural analysis of bacteriocytes in a deep-sea mussel Gigantidas platifrons with methanotrophic symbionts
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GRAPHICAL ABSTRACT
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PUBLIC SUMMARY
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3D imaging shows bacteriocyte structure with methanotrophic bacteria (MOB) in Gigantidas platifrons.
High- and low-density granule content MOB (MOBhd) at apex and MOB (MOBld) in the interior were identified.
MOBhd lyses for nutrients, MOBld divides to maintain symbiont population, all MOB in a connected channel system.
Gill bacteriocytes exhibit more organized MOB distribution and controlled symbiont management strategies.
Unprecedented insights into the structural basis of stable symbiosis in deep-sea mussels.
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ABSTRACT
Deep-sea mussels inhabit extreme environments through symbiosis with chemosynthetic bacteria, yet the three-dimensional (3D) ultrastructure of their bacteriocytes—the fundamental symbiotic units—remains elusive. This study employed advanced volume electron microscopy (vEM) to generate high-resolution, 3D models of bacteriocytes, revealing insights into the structural basis of stable symbiosis. We identified two distinct methanotrophic bacterial (MOB) morphotypes within the bacteriocytes: MOBhd (high-density granule content) and MOBld (low-density granule content). MOBhd, located in the apical region, undergoes lysis for nutrient release, while MOBld, situated in the interior, proliferates to maintain the symbiont population. Comparative analyses between gill and non-gill bacteriocytes revealed differential patterns of symbiont management, with gill bacteriocytes exhibiting more organized MOB distribution and orderly lysis. The 3D model unveiled a novel channel membrane system, potentially enhancing intracellular symbiont connectivity and facilitating distinct micro-niche occupation within the host cell. This organized structure maintains stable symbiosis, particularly in gill tissues. These findings advance our understanding of cellular mechanisms in symbiosis and adaptive strategies in extreme deep-sea environments. -
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Zhong Z., Sun W., Zhang Y., et al. (2025). 3D structural analysis of bacteriocytes in a deep-sea mussel Gigantidas platifrons with methanotrophic symbionts. The Innovation Geoscience 3:100110. https://doi.org/10.59717/j.xinn-geo.2024.100110
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Zhong Z., Sun W., Zhang Y., et al. (2025). 3D structural analysis of bacteriocytes in a deep-sea mussel Gigantidas platifrons with methanotrophic symbionts. The Innovation Geoscience 3:100110. https://doi.org/10.59717/j.xinn-geo.2024.100110
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Figure 1.
Two MOB morphotypes identified in deep-sea mussel G. platifrons bacteriocytes
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Figure 2.
Deconvolution of G. platifrons individuals of various lengths
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Figure 3.
Spatial distribution of two MOB morphotypes within bacteriocyte
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Figure 4.
MOB lysis without surrounding lysosomes
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Figure 5.
MOB exposed to external environment and MOB division within bacteriocytes
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Figure 6.
Theoretical model of MOB population dynamics and long-term gill bacteriocyte maintenance
