黄河小浪底库区旱季上游和下游原核生物群落与固碳功能微生物群的环境驱动因素

Environmental drivers of prokaryotic microbial communities and carbon-fixing microbial groups in the upper and lower reaches of the Xiaolangdi Reservoir of the Yellow River during the dry season

摘要:

【目的】 探究旱季黄河小浪底库区及下游原核生物及其固碳功能群的环境驱动因素。【方法】 采集旱季(2020年11月)黄河小浪底库区及下游水体和表层沉积物样品进行理化因子测定；通过细菌、古菌16S rRNA基因高通量测序和PICRUSt2预测探究原核生物群落组成及其固碳功能，同时通过固碳基因cbbL和cbbM高通量测序分析固碳微生物群落组成。【结果】 变形菌门(Proteobacteria，24.74%)、放线菌门(Actinobacteria，17.55%)和厚壁菌门(Firmicutes，11.43%)为优势细菌；泉古菌门(Crenarchaeota，63.26%)、热原体门(Thermoplasmatota，18.29%)和盐杆菌门(Halobacterota，11.31%)为主要优势古菌。此外，变形菌门(Proteobacteria，13.14%)、蓝藻门(Cyanobacteria，1.70%)和放线菌门(Actinobacteria，0.76%)是cbbL型固碳微生物的优势门；变形菌门(Proteobacteria，3.52%)、放线菌门(Actinobacteria，0.03%)和芽单胞菌门(Gemmatimonadota，0.02%)是cbbM型固碳微生物的优势门。其中，细菌群落结构的主要驱动因素是温度(temperature, T)、浊度(turbidity, Turb)、化学需氧量(chemical oxygen demand, COD)和总氨氮(total ammonia nitrogen, TAN)，但环境因子对古菌及固碳微生物的影响较弱。在细菌固碳途径中，还原柠檬酸循环(rTCA)、二羧酸/4-羟基丁酸循环(DC/4HB)、3-羟基丙酸双循环(3HP)和卡尔文循环(CBB)的丰度较高，且小浪底上游3-羟基丙酸/4-羟基丁酸循环(3HP/4HB)丰度显著高于下游。在古菌群落固碳途径中，rTCA、DC/4HB和不完全还原柠檬酸循环(incomplete rTCA)的丰度较高，且小浪底下游还原乙酰辅酶A途径(WL)丰度显著高于库区。浊度是影响细菌3HP和incomplete rTCA途径丰度的关键因素；温度、溶解氧(dissolved oxygen, DO)、浊度、COD和总磷(total phosphorus, TP)则是影响古菌固碳途径丰度的主要因素。【结论】 本研究揭示了旱季小浪底库区上、下游原核生物及其固碳功能群的环境驱动因素，结果有助于加深理解旱季黄河微生物驱动的碳固定过程及其环境驱动机制。

Abstract:

[Objective] To explore the environmental drivers of prokaryotic microbial communities and carbon-fixing microbial groups in the upper and lower reaches of the Xiaolangdi Reservoir of the Yellow River during the dry season. [Methods] Water and surface sediment samples were collected from the upper and lower reaches of Xiaolangdi Reservoir during the dry season (November, 2020), and the physiochemical factors were measured. The composition of prokaryotic microbial communities and their carbon fixation functions were investigated by high-throughput sequencing of bacterial and archaeal 16S rRNA genes and PICRUSt2 prediction. The composition of carbon-fixing microbial groups was analyzed by high-throughput sequencing of cbbL and cbbM. [Results] Proteobacteria (24.74%), Actinobacteria (17.55%), and Firmicutes (11.43%) were the dominant bacterial phyla. Crenarchaeota (63.26%), Thermoplasmatota (18.29%), and Halobacterota (11.31%) were the dominant archaea. Proteobacteria (13.14%), Cyanobacteria (1.70%), and Actinobacteria (0.76%) were the dominant phyla of cbbL-carrying carbon-fixing microorganisms. Proteobacteria (3.52%), Actinobacteria (0.03%), and Gemmatimonadota (0.02%) were the dominant phyla of cbbM-carrying carbon-fixing microorganisms. The main environmental drivers of the bacterial community structure were temperature (T), turbidity, chemical oxygen demand (COD), and total ammonia nitrogen, which, however, had mild influences on archaea and carbon-fixing microbial groups. In bacteria, the relative abundance of the reductive tricarboxylic acid cycle (rTCA), the dicarboxylate-hydroxybutyrate cycle (DC/4HB), the 3-hydroxypropionate bi-cycle (3HP), and the Calvin-Benson-Bassham (CBB) were higher than that of other detected carbon fixation pathways. Notably, the relative abundance of the hydroxypropionate-hydroxybutylate cycle (3HP/4HB) in the upper reaches was significantly higher than that in the lower reaches. In archaea, the relative abundance of carbon fixation pathways such as rTCA, DC/4HB, and incomplete rTCA was higher, and the abundance of the Wood-Ljungdahl pathway (WL) in the lower reaches was markedly higher than that in the upper reaches of the Xiaolangdi Reservoir. Turbidity was a key factor affecting the abundance of the bacterial 3HP and incomplete rTCA, while temperature, dissolved oxygen, turbidity, COD, and total phosphorus were the main factors affecting the abundance of carbon fixation pathways in archaea. [Conclusion] This study revealed the environmental drivers of prokaryotic microbial communities and carbon-fixing microbial groups in the upper and lower reaches of the Xiaolangdi Reservoir during the dry season. The results contribute to a deeper understanding of the microbial carbon fixation process and the environmental driving mechanisms in the Yellow River during the dry season.