Secrets of the sulfur cycle: bacteria from the Black Sea

All forms of life, from bacteria to humans, require sulfur as essential nutrient. Furthermore, many bacteria and archaea interact with sulfur compounds to obtain the energy they need for growth.


Some of these sulfur microbes – for instance sulfate-reducing microorganisms – produce sulfide (H2S), which has the smell of rotten eggs and can create ‘dead zones’ in the ocean because of its toxicity. However, other sulfur microbes consume H2S, using it as electron donor for energy. Sulfur microbes thus have a big impact on the marine environment, and even on the global climate. Who are these sulfur microbes?

Aim and progress

To answer this question, we focus on the Black Sea, the world’s largest anoxic basin. It is home to many different sulfur microbes which cannot tolerate oxygen and are yet to be studied. By now, we have brought new and exciting sulfur microbes from Black Sea samples into pure culture, allowing us to study their metabolism in detail. For instance, we isolated two strains of a novel bacterial family which cleave sulfate ester groups from polysaccharides to digest their food (Van Vliet et al., 2019). Their genomes contain more genes for sulfate-cleaving enzymes (sulfatases) than any other known organism. What’s also exciting is that we detected genes that could produce novel bioactive molecules such as antibiotics.

Current research and techniques

At the moment, we are studying the gene expression of these sulfur microbes with transcriptomics. Also, we enriched or isolated several interesting new sulfur-reducing microorganisms whose properties, metabolism and genome we are still exploring. Lastly, we are also studying the Black Sea sulfur microbes with a culture-independent metagenomics approach. During a thesis you could join one of these projects, in which you can learn and apply the following techniques: anaerobic cultivation, molecular identification of novel microorganisms, Fluorescence In Situ Hybridization (FISH), (meta-)genomics, transcriptomics and proteomics.