Bacterial diversity in Icelandic cold spring sources and in relation to the groundwater amphipod Crangonyx islandicus

Crangonyx islandicus is a groundwater amphipod endemic to Iceland, considered to have survived the Ice Ages in subglacial refugia. Currently the species is found in spring sources in lava fields along the tectonic plate boundary of the country. The discovery of a groundwater species in this inaccessible habitat indicates a hidden ecosystem possibly based on chemoautotrophic microorganisms as primary producers. To explore this spring ecosystem, we assessed its microbial diversity and analysed whether and how the diversity varied between the amphipods and the spring water, and if was dependent on environmental factors and geological settings. Isolated DNA from spring water and from amphipods was analysed using metabarcoding methods, targeting the 16S rRNA gene. Two genera of bacteria, Halomonas and Shewanella were dominating in the amphipod samples in terms of relative abundance, but not in the groundwater samples where Flavobacterium, Pseudomonas and Alkanindiges among others were dominating. The richness of the bacteria taxa in the microbial community of the groundwater spring sources was shaped by pH level and the beta diversity was shaped by geographic locations.

冰岛钩虾（Crangonyx islandicus）是冰岛特有地下水端足类（groundwater amphipod），被认为曾在冰期于冰下避难所中存活下来。目前该物种仅分布于冰岛构造板块边界沿线熔岩区域的泉水中。在这种难以抵达的生境中发现地下水特有物种，意味着存在一个可能以化能自养微生物作为初级生产者的隐秘生态系统。为探究该泉源生态系统，我们对其微生物多样性展开评估，并分析了钩虾与泉水样本间的微生物多样性是否存在差异、差异的具体模式，以及多样性是否受环境因素与地质背景调控。我们针对16S rRNA基因（16S rRNA gene），采用元条形码测序（metabarcoding）方法，对泉水和钩虾样本中提取的DNA进行了分析。分析结果显示，钩虾样本中的优势细菌类群为盐单胞菌属（Halomonas）与希瓦氏菌属（Shewanella），其相对丰度占据主导地位；但地下水样本的优势类群并非二者，而是以黄杆菌属（Flavobacterium）、假单胞菌属（Pseudomonas）及烷烃溶杆菌属（Alkanindiges）等为代表的类群。地下水泉源微生物群落的细菌类群丰富度受pH水平调控，而群落的β多样性（beta diversity）则由地理位置决定。