Preliminary Evidence for a Sulphur Cycle in Movile Cave, Romania

Abstract

SummaryIn order to investigate the food chain and energy balance of the chemolithoautotrophically-based ecosystem of the sulphur spring in Movile Cave as a model system for extraterrestrial life, a first sampling campaign was done. Microbial diversity and activity were analysed by MPN-enumeration methods and microcalorimetry, respectively. In addition, a speciation of the inorganic sulphur compounds by HPLC and IC techniques was performed. Metabolic activities were predominantly connected with thick microbial mats floating on the water surface of the cave. These mats showed an aerobic heat evolution of about 1200 µW/g and contained about 500 µmol/g elemental sulphur. In contrast, other samples collected from cave water, sediment and rock exhibited only activities of maximal 40 to 60 µW/g and contained only up to 2.5 µmol/g elemental sulphur. As the main primary producers aerobic and facultatively anaerobic sulphur oxidisers were identified at high numbers, occasionally exceeding 10 7 CFU/g. Methylotrophic bacteria were present in all samples at up to 10 6 CFU/g, indicating the important role of C1 metabolism for the cave ecosystem. Although reduced sulphur species were biologically oxidised to sulphuric acid, the pH values of the samples ranged from 6.5 to 8.2 due to the high buffering capacity of the cave walls, which consisted mainly of limestone. Surprisingly, not only neutrophilic but also extremely acidophilic bacteria were detected. Sulphate reducers were present in both aerobic and anaerobic zones. The data presented suggest a close interdependence of sulphur oxidation and reduction as well as carbon dioxide and other C1 compound metabolism in the most biologically active zone of the cave ecosystem, i.e. the floating microbial mats.

Life without light: microbial diversity and evidence of sulfur- and ammonium-based chemolithotrophy in Movile Cave

“…Microscopic observations indicated that the floating mat contained Thiothrix-and Beggiatoa-like filamentous bacteria (Sarbu et al, 1994) and subsequently a T. thioparus strain was isolated from Movile Cave water (Vlasceanu et al, 1997). Earlier studies have shown that aerobic and anaerobic sulfur oxidizers are abundant (up to 10 7 CFU (colony-forming unit) per gram sample) (Rohwerder et al, 2003). Our molecularbased analyses confirmed the presence of filamentous sulfur-oxidizing bacteria related to Thiothrix, Beggiatoa and Thioploca within the Gammaproteobacteria (Figure 1).…”

“…This group, compared with the filamentous sulfur oxidizers Thiothrix-Thioploca-Beggiatoa, was particularly active during SIP microcosm incubations. The presence of anaerobic sulfur oxidizers in Movile Cave has also been suggested earlier (Rohwerder et al, 2003) and a 16S rRNA sequence related to Sulfuricurvum was detected in our crude DNA clone library, although it was not labeled during SIP incubations, probably because of the fact that the incubation was carried out aerobically, and Sulfuricurvum oxidizes sulfur anaerobically (Kodama and Watanabe, 2004). It is to be noted that no sequences related to known sulfur-oxidizing archaea were observed in the archaeal 16S RNA clone library, which may reflect the fact that the One notable difference in the Movile Cave microbial community compared with other chemoautotrophically based cave systems, such as Lower Kane Cave (USA), is that Epsilonproteobacteria were less abundant in Movile Cave (Engel et al, 2003(Engel et al, , 2004.…”

Competition-cooperation in the chemoautotrophic ecosystem of Movile Cave – first metagenomic approach on sediments

“…Methanotrophs were also postulated as primary producers in the water and microbial mats [19–21, 24, 60] as 1– 2 % methane concentration was highlighted, especially in the Air-Bells [57]. In this study we were able to assemble methanotrophic MAGs from both lower and upper galleries.…”

Evidence for Iron- and Sulfur-Oxidizing Bacteria and Archaea in a Currently Active Lignite Mining Area of Lusatia (Eastern Germany)

“…The real cell number was most probably underestimated, because microorganisms growing as a biofilm cannot be separated into single cells [1]. Similar cell numbers per g were described for uranium mine waste heaps and Movile Cave, respectively [1,11]. Investigations were carried out to quantify metabolic activity of microorganisms by microcalorimetry.…”