Lucian C. Staicu
Faculty of Biology, University of Warsaw, Poland
Host: Gabriela Almeida, UCIBIO - FCT NOVA
Selenium respiration in bacteria: an unsolved puzzle
Selenium (Se) respiration in bacteria was revealed for the first time at the end of 1980s (Macy et al., 1989; Gunsalus et al., 2007). Although thermodynamically-favorable and documented in phylogenetically-diverse bacteria, this metabolic process appears to be accompanied by a number of challenges and numerous unanswered questions (Staicu and Barton, 2017). Selenium oxyanions, SeO4 2- and SeO3 2-, are reduced to elemental Se, Se(0), through anaerobic respiration, the end product being solid and displaying a consideral size (up to 400 nm) at the bacterial scale. Moreover, various allotropic forms and shapes of biogenic Se(0) (e.g. amorphous globular, crystalline needle-shaped etc) are potentially detrimental for cellular integrity and homeostasis. Compared to other electron acceptors used in anaerobic respiration (e.g. N, S, Fe, Mn, As), Se is the only element whose end product is solid. Furthermore, unlike other known bacterial intracellular accumulations such as volutin (inorganic polyphosphate), S(0), glycogen or magnetite, Se(0) has not been shown to play a nutritional or ecological role for its host nor it displays any other function.
In the context of anaerobic respiration of Se oxyanions, biogenic Se(0) appears to be a by-product, a waste that needs proper handling and this raises the question of the evolutionay implications of this process. Why would bacteria select for a metabolic process that is useful, in the first place, and then highly detrimental? Interestingly, in certain artificial ecosystems (e.g. upflow bioreactors), Se(0) might help bacterial cells to increase their buoyancy and thus avoid biomass wash-out, ensuring survival.
However, this process has only been revealed for “recent” man-made ecosystems and mixed microbial communities (granular sludge) (Cordoba and Staicu, 2018). This presentation will explore in depth the thermodynamics, enzyme systems, genetic determinants and the evolutionary implications of selenium respiration in bacteria, attempting to answer a number of questions including i) where does the nucleation process of Se(0) occur in bacteria, ii) are there any viable possibilities for Se(0) extracellular transport, and iii) what are the evolutionary implications for bacteria that adopted this strategy to generate cellular energy.
Cordoba P, Staicu LC. Flue Gas Desulfurization effluents: an unexploited selenium resource. Fuel, 2018, 223:268-276.
Gunsalus R, Cecchini G, Schröder I. Bacterial Respiration. In: “Methods for General and Molecular Microbiology”, Reddy C, Beveridge T, Breznak J, Marzluf G, Schmidt T, Snyder L (eds.), ASM Press, 2007; p. 539-557.
Macy JM, Michel TA, Kirsch DG. Selenate reduction by Pseudomonas species: a new mode of anaerobic respiration. FEMS Microbiol Lett. 1989; 61:195-198.
Staicu LC, Barton LL. Microbial metabolism of selenium – for survival or profit. In: “Bioremediation of selenium contaminated wastewaters”, van Hullebusch ED (ed.),
Springer, 2017; p. 1-31.
Lucian Staicu did his bachelor in Biology at University of Bucharest (Romania) and an MSc degree in electrochemistry at University Paris Est Marne-la-Vallée, France. In 2014 Lucian obtained his PhD in Biotechnology (joint degree, University Paris Est, France and UNESCO-IHE, Netherlands; with Eric van Hullebusch and Piet Lens). Next, Lucian did two postdoctoral stages in France at University Franche-Comté (Besançon) (Gregorio Crini’s group) and a second one at University Blaise Pascal (Clermont Ferrand) (Isabelle Batisson’s and Vanessa Prevot’s groups). Since 2018, Dr. Staicu works as principal investigator at University of Warsaw, Poland, conducting research on anaerobic respiration of arsenic and selenium in phylogenetically-diverse bacteria, lead biomineralization, as well as on critical raw material recovery.