In 1988, Günter Wäschterhäuser proposed a new theory to explain the origin of life: the theory of surface metabolism (Wäschterhäuser 1988). This theory, also known as “the iron-sulphur world”, states that the chemical reactions directed by the reducing power of iron-sulphur (Fe-S)/H2S were responsible for the catalytic events that led to the first biopolymer structures. One possible remnant of this Fe-S world is the set of Fe-S clusters present in both eukaryotic and prokaryotic proteins (Beinert 2000). Fe-S clusters participate in a wide range of molecular and biochemical reactions that bacteria rely on to control important aspects of their metabolism under various conditions, including stress. Thus, we might consider Fe-S clusters one of the “premier” tools of the bacterial survival kit, and the elucidation of how this cluster operates in bacteria other than traditional prokaryote models (e.g., Escherichia coli) is of great relevance to bacterial infection research. In the Memórias do Instituto Oswaldo Cruz 109: 408-413 issue, Riboldi et al. report findings on the operation of Fe-S cluster and sulphur assimilation genes in Enterococcus faecalis, a Gram-positive bacterium of the phylum Firmicutes that is a commensal organism for humans but may also represent a threat under certain conditions (e.g., immunodeficiency). The authors demonstrate that E. faecalis initiates Fe-S cluster assembly under growth stress conditions and activates the transcriptional machinery of the sulphur assimilation genes at low concentrations of free oxygen radicals.
If the iron-sulphur world proposition is correct, high temperatures and volcanic vents created a difficult environment for any primitive form of life (Beinert 2000). Notwithstanding this potential for hard tool shaping (from a chemical and evolutionary perspective), a ubiquitous soft tool might have been shaped by some other evolutionary process to aid bacteria in surviving stressful conditions. One possible example of such a “soft-tool-shaping phenomenon” was reported by Guimarães et al. (2014), who demonstrated that the ability (or virulence) of Helicobacter pylori to colonise the hard environment defined by the gastric mucosa is modulated by exposure to water.
The current genomic configuration of these “hard and soft” chemical tools in modulating bacterial responses to environmental changes tells us little about their evolutionary history and how primitive biological structures might have selected them for use under stressful conditions. However, simple organisms such as bacteria harbour surprisingly complex mechanisms that guarantee genome replication and the subsequent transmission of their genes to new generations. What we would consider as undesirable events, e.g., infection and likely disease for a human being, might be viewed as an elaborate bacterial response to several forms of stress. The ultimate goal? Survival!
Adeilton Alves Brandão | Publisher Editor
Beinert H 2000. Iron-sulfur proteins: ancient structures, still full of surprises. J Biol Inorg Chem 5: 2-15.
Guimarães NM, Azevedo NF, Vieira MJ, Figueiredo C 2014. Water-induced modulation of Helicobacter pylori virulence properties. Mem Inst Oswaldo Cruz 109: 414-419.
Riboldi GP, Bierhals CG, de Mattos EP, Frazzon APG, d‘Azevedo PA, Frazzon J 2014. Oxidative stress enhances the expression of sulfur assimilation genes: preliminary insights on the Enterococcus faecalis iron-sulfur cluster machinery regulation. Mem Inst Oswaldo Cruz 109: 408-413.
Wäschterhäuser G 1988. Before enzymes and templates: theory of surface metabolism. Microbiol Rev 52: 452-484.