Department of Ocean Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, SAR, China.
SZU-HKUST Joint PhD Program in Marine Environmental Science, Shenzhen University, Shenzhen, China.
BMC Genomics. 2021 Jan 7;22(1):37. doi: 10.1186/s12864-020-07333-z.
Nutrient stoichiometry of phytoplankton frequently changes with aquatic ambient nutrient concentrations, which is mainly influenced by anthropogenic water treatment and the ecosystem dynamics. Consequently, the stoichiometry of phytoplankton can markedly alter the metabolism and growth of zooplankton. However, the effects of nutrient-imbalanced prey on the interplay between zooplankton and their gut microbiota remain unknown. Using metatranscriptome, a 16 s rRNA amplicon-based neutral community model (NCM) and experimental validation, we investigated the interactions between Daphnia magna and its gut microbiota in a nutrient-imbalanced algal diet.
Our results showed that in nutrient-depleted water, the nutrient-enriched zooplankton gut stimulated the accumulation of microbial polyphosphate in fecal pellets under phosphorus limitation and the microbial assimilation of ammonia under nitrogen limitation. Compared with the nutrient replete group, both N and P limitation markedly promoted the gene expression of the gut microbiome for organic matter degradation but repressed that for anaerobic metabolisms. In the nutrient limited diet, the gut microbial community exhibited a higher fit to NCM (R = 0.624 and 0.781, for N- and P-limitation, respectively) when compared with the Control group (R = 0.542), suggesting increased ambient-gut exchange process favored by compensatory feeding. Further, an additional axenic grazing experiment revealed that the growth of D. magna can still benefit from gut microbiota under a nutrient-imbalanced diet.
Together, these results demonstrated that under a nutrient-imbalanced diet, the microbes not only benefit themselves by absorbing excess nutrients inside the zooplankton gut but also help zooplankton to survive during nutrient limitation.
浮游植物的营养化学计量经常随水生环境营养浓度而变化，这主要受人为水处理和生态系统动态的影响。因此，浮游植物的化学计量可以显著改变浮游动物的代谢和生长。然而，营养失衡的猎物对浮游动物及其肠道微生物群之间相互作用的影响尚不清楚。本研究使用宏转录组学、基于 16s rRNA 扩增子的中性群落模型（NCM）和实验验证，研究了营养失衡藻类饮食中大型溞及其肠道微生物群之间的相互作用。
研究结果表明，在贫营养水中，富营养化的浮游动物肠道在磷限制下刺激了微生物聚磷酸盐在粪便颗粒中的积累，在氮限制下刺激了微生物对氨的同化。与营养充足组相比，氮和磷限制都显著促进了肠道微生物群对有机质降解的基因表达，但抑制了对厌氧代谢的基因表达。在营养限制的饮食中，与对照组（R=0.542）相比，肠道微生物群落与 NCM 的拟合度更高（氮限制时 R=0.624，磷限制时 R=0.781），表明补偿性摄食促进了环境-肠道交换过程。此外，一项额外的无菌放牧实验表明，在营养失衡的饮食中，肠道微生物仍然可以促进大型溞的生长。
总之，这些结果表明，在营养失衡的饮食中，微生物不仅可以通过吸收浮游动物肠道内的多余营养物质而使自身受益，而且还可以帮助浮游动物在营养限制期间存活。
