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<p>Bacteria are integral components of cnidarian holobionts, but the nature of their interactions with algal symbionts remains unresolved. While microbial vitamin provisioning has been proposed as a key service, the extent to which this occurs in symbioses like that of <i>Symbiodinium linucheae</i> and its microbiome remains unclear. To address this gap, we examined the growth dynamics of algal–bacterial cocultures in nutrient-depleted conditions. <i>Symbiodinium linucheae</i>, the algal symbiont of Aiptasia anemones (<i>Exaiptasia diaphana</i>), putatively possesses the cobalamin (B<sub>12</sub>)-dependent methionine synthase gene, making it dependent on B<sub>12,</sub> an essential vitamin produced by prokaryotes. We previously isolated a bacterial B<sub>12</sub>-producer, <i>Roseibium</i>, a fundamental member of the Symbiodiniaceae microbiome, and sequenced its genome to confirm its metabolic potential for B<sub>12</sub> synthesis. Here, we grew axenic cultures of <i>S. linucheae</i> (strain SSA01) and <i>Roseibium</i> in B<sub>12</sub>-limited media for 12&#xa0;weeks to document growth dynamics, followed by differential gene expression analysis comparing pure culture controls (axenic SSA01 or axenic <i>Roseibium</i>) with coculture treatments. SSA01 exhibited limited transcriptomic differences in coculture, like enrichment of GTPase activity, ligase and genes related to replication, yet it grew at higher densities than SSA01 in monocultures, regardless of B<sub>12</sub> availability. <i>Roseibium</i> also achieved higher densities in coculture, and transcriptomic differences suggest it benefits from associations with SSA01 in low nutrient environments. Taken together, these results suggest SSA01 may not be true B<sub>12</sub> auxotrophs but may receive alternative, possibly indirect, metabolic benefits from <i>Roseibium</i>.</p>

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Symbiodiniaceae-Roseibium exhibit synergistic growth effects without B12 supplementation

  • 期刊论文

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  • 发表日期：

    2025年12月15日

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  • Emily G. Aguirre,
  • Marissa J. Fine,
  • Tingting Xiang,
  • Carly D. Kenkel

摘要

Bacteria are integral components of cnidarian holobionts, but the nature of their interactions with algal symbionts remains unresolved. While microbial vitamin provisioning has been proposed as a key service, the extent to which this occurs in symbioses like that of Symbiodinium linucheae and its microbiome remains unclear. To address this gap, we examined the growth dynamics of algal–bacterial cocultures in nutrient-depleted conditions. Symbiodinium linucheae, the algal symbiont of Aiptasia anemones (Exaiptasia diaphana), putatively possesses the cobalamin (B12)-dependent methionine synthase gene, making it dependent on B12, an essential vitamin produced by prokaryotes. We previously isolated a bacterial B12-producer, Roseibium, a fundamental member of the Symbiodiniaceae microbiome, and sequenced its genome to confirm its metabolic potential for B12 synthesis. Here, we grew axenic cultures of S. linucheae (strain SSA01) and Roseibium in B12-limited media for 12 weeks to document growth dynamics, followed by differential gene expression analysis comparing pure culture controls (axenic SSA01 or axenic Roseibium) with coculture treatments. SSA01 exhibited limited transcriptomic differences in coculture, like enrichment of GTPase activity, ligase and genes related to replication, yet it grew at higher densities than SSA01 in monocultures, regardless of B12 availability. Roseibium also achieved higher densities in coculture, and transcriptomic differences suggest it benefits from associations with SSA01 in low nutrient environments. Taken together, these results suggest SSA01 may not be true B12 auxotrophs but may receive alternative, possibly indirect, metabolic benefits from Roseibium.