Karst spring microbial mat microeukaryotic diversity differs across an oxygen-sulphide ecocline and reveals potential for novel taxa discovery

Abstract

Strong geochemical gradients of dissolved oxygen and sulphide establish habitats where specialized bacterial and archaeal taxonomic groups occupy specific redox-sensitive niches, primarily based on metabolic and ecological requirements. In contrast, knowledge of microeukaryote diversity and their ecology in redox-stratified habitats is poor, as species-specific occupation of such geochemical gradients has not been well established. Here we assessed total microbial diversity from rRNA genes retrieved from two morphologically distinct microbial mats formed along an oxygen-sulphide gradient in the outflow channel from the Žveplenica sulphidic karst spring, Slovenia. Microbial mats contained diverse bacteria and archaea associated with chemolithoautotrophic and primary productivity, and overall microeukaryotic diversity was higher under oxygenated conditions. The oxygenated mats were comprised of undescribed and undifferentiated fungi, Annelida, Nematoda, Apicomplexa, and Gastrotricha, some being represented by novel lineages. Under anoxic conditions, diversity was dominated by Ciliophora, Nematoda, and Fungi-Ascomycota, also affiliated with novel lineages. Colonization of the distinct mat types related to ecological tolerance of specific geochemical conditions, and the associations between bacterial and archaeal diversity with distinct microeukaryotes may be related to grazing options and food web structure within the karst system. Key words: karst, spring, sulphide, geochemical gradient, diversity, microeukaryotes. Pestra mikrobna diverziteta vzdolž ekokline kisik-sulfid kraskega izvira odkriva potencial za okritje novih taksonov Izraziti geokemijski gradienti raztopljenega kisika in sulfida so osnova za habitate, kjer v odvisnosti od redoks potenciala, predvsem pa glede na metabolne in ekoloske zahteve, specializirane bakterijske in arhejske taksonomske skupine zasedajo obcutljive ekoloske nise. Nasprotno pa je poznavanje diverzitete mikroevkariontov in njihove ekologije v habitatih, stratificiranih glede na redoks potencial, pomanjkljivo, saj vrstno specificne kolonizacije taksnih gradientnih okolij se nismo dobro proucili. Celotno mikrobno diverziteto smo ovrednotili na podlagi zaporedij rRNA genov, ki so bila pridobljena iz dveh morfolosko razlicnih mikrobnih biofilmov, ki nastajata vzdolž gradienta kisik-sulfid v žveplenem kraskem izviru Žveplenica, Slovenija. Mikrobni biofilmi so vsebovali pestro združbo bakterij in arhej, ki jim pripisujemo kemolitoavtotrofen metabolizem s primarno produkcijo, celotna mikroevkariontska diverziteta pa je bila v oksigeniranih okoljskih razmerah visja. Oksigeniran biofilm so vecinoma sestavljale se neopisane in nepoznane glive ter predstavniki skupin Annelida, Nematoda, Apicomplexa in Gastrotricha; nekatere izmed njih pripadajo celo novim linijam. V anoksicnih razmerah so prevladovali predstavniki skupin Ciliophora, Nematoda in Glive-Ascomycota, ki tudi pripadajo novim genetskim linijam. Kolonizacija razlicnih tipov biofilmov glede na ekolosko toleranco specificnih geokemijskih razmer ter povezava med bakterijsko in arhejsko diverziteto z znacilnimi mikroevkariontskimi predstavniki sta lahko povezana z razlicnimi možnostmi prehranjevanja in s strukturo prehranjevalne verige v kraskem sistemu. Kljucne besede: kras, izvir, sulfid, geokemijski gradient, diverziteta, mikroevkarionti.