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<p><i>Gracilaria chilensis</i> and <i>Gracilaria vermiculophylla</i> are two related and commercially relevant red algal species due to their agar production. Native populations of <i>G. vermiculophylla</i>, as well as natural populations of <i>G. chilensis</i> are nearly always attached by holdfasts to hard substrate and the individuals are all capable of producing reproductive structures. In contrast, farmed <i>G. chilensis</i> individuals are mostly devoid of reproductive structures and propagated vegetatively in soft substrata. Similarly, a strong capacity of non-native <i>G. vermiculophylla</i> to reproduce vegetatively by fragmentation has facilitated its range expansion into habitats that are devoid of hard substrate. This comparative study investigated the importance of microbial biofilm for the formation of reproductive structures in natural and farmed <i>G. chilensis</i> and native and non-native <i>G. vermiculophylla</i>. We tested whether experimental removal of bacterial biofilm affected the formation of tetrasporangia. Histological sections revealed similarities in the tetrasporangia formation processes between both species, with later appearance of reproductive structures in <i>G. vermiculophylla</i>. In <i>G. chilensis</i>, natural populations showed optimal tetrasporangia development, whereas farmed populations produced significantly fewer reproductive structures in all the treatments. Removal of biofilm increased the formation of tetrasporangia in farmed populations, while it caused reduced growth in all <i>G. chilensis</i> populations. In contrast, biofilm removal resulted in a decreased production of tetrasporangia in native populations of <i>G. vermiculophylla</i> and an increased growth in native and non-native populations. Overall, our results suggest that bacterial interactions influence seaweed fertility, but this effect is context dependent, leading to differing impacts according to the non-natural environmental history. They also revealed an important role in regulating trade-offs between growth and fertility, especially in farmed and non-native populations. Finally, microbial community reinoculation did not restore functional effectiveness on growth and reproduction, a likely consequence of uncoordinated colonization process, suggesting that eventual application based on microbial manipulation should take extra-steps to control the composition and successional process of biofilm restoration.</p>

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Microbial biofilm influences tetrasporophyte fertility in clonal and sexual populations of two Gracilaria species

  • 期刊论文

  • 发表日期：

    2025年9月19日

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  • Sara Usandizaga,
  • Juan Pablo Olivos,
  • Jessica Beltrán,
  • Florian Weinberger,
  • Marie-Laure Guillemin,
  • Sylvain Faugeron

摘要

Gracilaria chilensis and Gracilaria vermiculophylla are two related and commercially relevant red algal species due to their agar production. Native populations of G. vermiculophylla, as well as natural populations of G. chilensis are nearly always attached by holdfasts to hard substrate and the individuals are all capable of producing reproductive structures. In contrast, farmed G. chilensis individuals are mostly devoid of reproductive structures and propagated vegetatively in soft substrata. Similarly, a strong capacity of non-native G. vermiculophylla to reproduce vegetatively by fragmentation has facilitated its range expansion into habitats that are devoid of hard substrate. This comparative study investigated the importance of microbial biofilm for the formation of reproductive structures in natural and farmed G. chilensis and native and non-native G. vermiculophylla. We tested whether experimental removal of bacterial biofilm affected the formation of tetrasporangia. Histological sections revealed similarities in the tetrasporangia formation processes between both species, with later appearance of reproductive structures in G. vermiculophylla. In G. chilensis, natural populations showed optimal tetrasporangia development, whereas farmed populations produced significantly fewer reproductive structures in all the treatments. Removal of biofilm increased the formation of tetrasporangia in farmed populations, while it caused reduced growth in all G. chilensis populations. In contrast, biofilm removal resulted in a decreased production of tetrasporangia in native populations of G. vermiculophylla and an increased growth in native and non-native populations. Overall, our results suggest that bacterial interactions influence seaweed fertility, but this effect is context dependent, leading to differing impacts according to the non-natural environmental history. They also revealed an important role in regulating trade-offs between growth and fertility, especially in farmed and non-native populations. Finally, microbial community reinoculation did not restore functional effectiveness on growth and reproduction, a likely consequence of uncoordinated colonization process, suggesting that eventual application based on microbial manipulation should take extra-steps to control the composition and successional process of biofilm restoration.