The Movile Cave represents a distinct habitat that shelters a multidisciplinary community of microbial
eukaryotes adapted to very specific low-oxygen, high-sulfide
, and methane-saturated environments. Their significance in ecosystem stability is as a result of their communities and association with chemosynthetic bacteria and archaea.
Prokaryotes The Movile Cave's unique groundwater system supports a complex community of chemoautotrophic primary producers. The different "rooms" of the cave have distinctive chemo-physiological conditions, allowing for the cultivation of unique bacterial genera in each environment.
Biofilm-associated bacterial community The surface waters and most of the cave walls are covered in varying sizes of bacterial biofilms ranging from small, white floating patches in the Lake Room and Air-bell I to yellowish biofilms up to thick found in Air-bell II. Kumaseran et al. discovered the representative species
Ca. Methylomas sp. LWB in microbial mats, presenting evidence for aerobic methylotrophy in the cave. Similar studies by Aerts et al. found complex groups of unique genera in
biofilm samples collected at 3 sub-locations: •
Methylophilaceae – methanol and methylamine reducer •
Rhodomicrobium – iron oxidizing purple non-sulfur bacteria, using HS- as an alternate electron acceptor • (2) Air-bell II wall biofilm: •
Woodsholea – halophilic bacteria, unclear metabolism • (3) Air-bell I submerged biofilm: •
Nitrospiraceae – genus of ammonia and nitrite oxidizers
Cave water-associated bacterial community Cave lake water samples reveal an equally complex microbial ecosystem of methanotrophs and sulfur-oxidizers, providing substrates to support life for microbes and invertebrates. Methanotrophic strains belonging to genera
Methylomonas, Methylococcus, Methylocystis/Methylosinus were found to be dominant methanotrophs in water samples and encode key methane monooxygenase genes,
pmoA and
mmoX. Members of the sulfur-oxidizer genera
Thiovulum were much more abundant and more metabolically active in Air-bell II than the Lake Room, but are dominant in both hypoxic and normoxic cave lake waters. The newly proposed species
Ca. Thiovulum stygium is found to possess nitrate reduction operons (
nar and
nap) as well as polysulfide reductase and sulfite exporter genes (
nrfD and
tauE respectively), suggesting its multifunctionality as an aerobic and anaerobic sulfide oxidation. High abundances of microorganisms belonging to the aerobic iron-oxidizing bacterial family
Gallionellaceae were found in sediment samples, specifically members of the genera
Sideroxydans and
Gallionella. Products of sulfur respiration coupled with hydrogen sulfide were found in lake-distant samples, however a full oxidation pathway could not be metagenomically assembled. •
Micrarchaeota – phylum of acidophilic archaea (Kadnikov et al., 2020) •
Methylocella – genus of class
Alphaproteobacteria comprising facultative acidophilic methanotrophs (Dedysh et al., 2005) • Order
Dongiales, formerly known as family
Rhodospirillaceae, a group of non-sulfur purple bacteria Alveolate sequences found in the cave were mostly associated with ciliates, with few that belonged to phylum
Apicomplexa. Stramenophiles found in the Movile Cave were also very diverse, and clustered into three abundant groups—
Bicosoecids, Labyrinthulids, and
Chrysophytes. Most abundant and diverse clades found within these groups were Bicosoecids, including 156 sequences while also sharing similarities with another environmental sequence from a shallow subtropical lake. Consistent with the cave's low-oxygen conditions, the environmental sequences most closely related to the Movile OTUs were sourced from oxygen-deprived habitats or species that thrive in microaerophilic or anaerobic conditions. Of these, 96 species were detected exclusively inside the cave. 90 species were found in the dry sections, including 51 from cave air, 42 from cave sediments, and 41 from various substrates such as dead invertebrates, corroded cave walls, and isopod feces. Airbell II contained 28 fungal species in which 23 species were present in sediments and 9 in the floating microbial mat. While most fungal species were widely distributed across the cave's underground habitats, two species including an undescribed species of
Aspergillus sect. Candidisa and
Talaromyces ruber were found exclusively in the sediments of Airbell II, while one species was found exclusively in the microbial mat in Airbell II. Due to a lack of fungal surveys following the cave's initial discovery in 1986, it remains uncertain whether these fungi are native or were introduced through contamination by researchers. == Symbiotic relationships ==