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.…”

“…Sequences related to M. petroleiphilum (a facultative methylotroph in the Betaproteobacteria) were also found in the soxB and RuBisCO clone libraries. An earlier culture-based study also showed that the numbers of culturable methylotrophs in the floating mat were around 10 6 CFU per gram dry weight of mat (Rohwerder et al, 2003). Archaeal communities in cave systems, in general, have not been studied in detail.…”

“…Later, Vlasceanu et al, (1997) isolated a Thiobacillus thioparus strain, which is particularly abundant in the microbial mat and the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), a key enzyme in CO 2 fixation for many chemoautotrophs, has been detected for this organism (Sarbu et al, 1994). Although sulfur oxidizers are thought to be the major primary producers in Movile Cave (Sarbu et al, 1996;Rohwerder et al, 2003), the presence of up to 1.5% (v/v) methane in the cave atmosphere suggested that methanotrophs may also be present. Hutchens et al, (2004) used DNA stable-isotope probing (DNA-SIP) to analyze the methanotroph populations and a diverse range of methanotrophs belonging to Alphaproteobacteria and Gammaproteobacteria were identified.…”

Productivity-diversity relationships from chemolithoautotrophically based sulfidic karst systems

“…The atmosphere in the air bells contains 7-10% O 2 , 2-3.5% CO 2 , 1-2% CH 4 , with trace H 2 S, and only a few millimeters of the cave water below the mats are oxygenated (Sarbu et al, 1996;Popa, 1997;Badescu, 1998). Although the microbial communities from Movile Cave have been of interest for more than a decade (e.g., Sarbu et al, 1996;Vlasceanu et al, 1997;Rohwerder et al, 2003) and various metabolic guilds have been investigated (Hutchens et al, 2004), there has not been a concerted effort to describe the overall microbial diversity of the mats using a 16S rRNA framework. To our knowledge, we report here the first 16S rRNA gene sequence diversity data for bacteria for the floating microbial mats from Movile Cave.…”