Abstract：
Macroalgal holobiont studies involve understanding interactions between the host, its microbiota, and the environment. We analyzed the effect of bacteria-kelp interactions on phenotypic responses of two genetically distinct populations of giant kelp, Macrocystis pyrifera (north and south), exposed to different nitrogen (N) concentrations. In co-culture experiments with different N concentration treatments, we evaluated kelp growth responses and changes in three specific molecular markers associated with the N cycle, both in epiphytic bacteria (relative abundance of nrfA-gene: cytochrome c nitrite reductase) and macroalgae (expression of NR-gene: nitrate reductase; GluSyn-gene: glutamate synthase). Both kelp populations responded differently to N limitation, with M. pyrifera-south sporophytes having a lower specific growth rate (SGR) under N-limiting conditions than the northern population; M. pyrifera-north sporophytes showed no significant differences in SGR when exposed to low-N and high-N concentrations. This corresponded to a higher GluSyn-gene expression in the M. pyrifera-north sporophytes and the co-occurrence of specific nrfA bacterial taxa. These bacteria may increase ammonium availability under low-N concentrations, allowing M. pyrifera-north to optimize nutrient assimilation by increasing the expression of GluSyn. We conclude that bacteria-kelp interactions are important in enhancing kelp growth rates under low N availability, although this effect may be regulated by the genetic background of kelp populations.
摘要：
巨藻全生物研究涉及理解宿主之间的相互作用，它的微生物群，和环境。我们分析了细菌-海带相互作用对两个遗传上不同的巨型海带种群的表型反应的影响，大孢子虫（北部和南部），暴露于不同的氮（N）浓度。在不同氮浓度处理的共培养实验中，我们评估了海带生长反应和与N循环相关的三个特定分子标记的变化，在附生细菌（nrfA基因的相对丰度：细胞色素c亚硝酸还原酶）和大型藻类（NR基因的表达：硝酸还原酶；GluSyn基因：谷氨酸合酶）中。两种海带种群对N限制的反应不同，在N限制条件下，Pyrifera-南方孢子体的比生长率（SGR）低于北方种群；当暴露于低氮和高氮浓度时，Pyrifera-北方孢子体的SGR没有显着差异。这对应于pyrifera-北孢子体中更高的GluSyn基因表达以及特定nrfA细菌分类群的共同出现。这些细菌在低氮浓度下可能会增加铵的利用率，允许M.pyrifera-north通过增加GluSyn的表达来优化营养同化。我们得出的结论是，在低氮利用率下，细菌-海带相互作用对提高海带生长速率很重要。尽管这种效应可能受海带种群遗传背景的调节。
