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Microbiology of Movile Cave

Exploring the food web of a unique, bacterially driven environment

Movile Cave is a totally unique environment, situated in the south of Romania. Not only is Movile Cave a fascinating example of a bacterially-driven environment, it is also completely isolated from the outside world – it exists as a sealed “bubble” of life locked below the surface of the Earth. Inspite of being totally sealed and being devoid of light, the Cave is a thriving ecosystem filled with all manner of life, from tiny crustacea to isopods, molluscs and arachnids. On the rest of the planet, ecosystems are supported by primary producers, such as plants or algae, that convert carbon dioxide from the air into living matter that can be eaten by higher organisms – this process is driven by light and is known as photosynthesis.

In the dark reaches of Movile Cave, the primary producers are bacteria that convert carbon dioxide into living matter in the form of vast floating “mats” on the surface of the Cave waters. Primary production in the dark is driven by chemical energy obtain by the bacteria from the oxidation of sulfur compounds and ammonia in the Cave waters – a process called chemosynthesis. In addition to this, we believe that a proportion of bacteria in these floating mats form their biomass by consumption of methane found in the geological gases that flow through the Cave – a process known as methanotrophy.

Fig. 1. Location of the Movile Cave, Romania

Our goals at UEA are to better understand the roles of chemosynthetic and methanotrophic bacteria in the floating mats of Movile Cave and their interactions with other species at the base of the food web. We work in collaboration with Dr Alexandra Hillebrand at the Emil Racovita Institute of Speleology, Bucharest. This project is funded by the NERC.

Our research at UEA focuses on three main areas of biogeochemistry within the Cave:

•  Methane consumption – methanotrophy and methylotrophy.
•  Sulfur oxidation – chemolithoautotrophy and chemolithoheterotrophy.
•  Nitrogen cycling – denitrification, nitrification, methylotrophy, chemolithoautotrophy.

Our model of the biogeochemical processes that occur in the cave is summarised in the figure below:

The dashed lines represent assimilation (consumption) of carbon into bacterial or archaeal biomass; the solid lines represent microbial transformations of chemicals. Letters in italics are the genes we are using as functional gene marker – DNA sequences specific to certain functional groups of organism. Finding evidence of a particular marker in an environment indicates that organisms of a particular functional guild are present. pmoA and mmoX encode parts of the methane monooxygenase enzymes used by methanotrophs; mxaF encodes part of the methanol dehydrogenase common to methanotrophs and methylotrophs; amoA encodes part of the ammonia monooxygenase found in ammonia-oxidising Bacteria and Archaea; mauA encodes part of the monomethylamine dehydrogenase found in some methylotrophs that can grow on methylated amines; nirS and nirK encode nitrite reductases used by denitrifying Bacteria (i.e. those that use nitrate instead of oxygen for respiration); nifH encodes part of the nitrogenase found in organisms able to use nitrogen gas as a nitrogen source; dsrAB encodes part of the dissimilatory sulfate reductase found in sulfate-reducing Bacteria (i.e. those that use sulfate instead of oxygen for respiration) and soxB encodes an enzyme from the Kelly-Friedrich pathway of sulfur oxidation, used by chemolithoautotrophs.