The role of 4-hydroxyphenylpyruvate dioxygenase in enhancement of solid-phase electron transfer by Shewanella oneidensis MR-1

Abstract

Summary 1While mechanistic details of dissimilatory metal reduction are far from being understood, it 2 is postulated that the electron transfer to solid metal oxides is mediated by outer membrane-3 associated c-type cytochromes and redox active electron shuttling compounds. This study 4 focuses on the production of homogensitate in Shewanella oneidensis MR-1, an intermediate 5 of tyrosine degradation pathway, which is a precursor of a redox cycling metabolite, 6 pyomelanin. In this study, we determined that two enzymes involved in this pathway, 4-7 hydroxyphenylpyruvate dioxygenase (4HPPD) and homogentisate 1,2-dioxygenase are 8 responsible for homogentisate production and oxidation, respectively. Inhibition of 4-HPPD 9 activity with the specific inhibitor sulcotrione ([2-(2-chloro-4-methane sulfonylbenzoyl)-10

Properties and Function of Pyomelanin

“…Consequently, tyrosine or phenylalanine may not be required to be present in the environment for pyomelanin production to proceed, especially in biofilms where cell density is high. The rate of exocellular electron transfer by dissimilatory metal reducing bacteria is enhanced by only small quantities of pyomelanin (femtograms per cell) due to the redox cycling nature of this polymer (Turick, et al 2002;Turick, et al 2009). Surface sorption of pyomelanin to the bacterial cell allows for its repeated use as an electron conduit (Turick, et al 2003;Turick, et al 2009).…”

“…The redox cycling properties of pyomelanin enable this process to occur. When the redox cycling properties of pyomelanin are coupled to energy conservation by dissimilatory metal reducing bacteria, the rate of metal oxide reduction increases along with growth rates (Turick, et al 2002;Turick, et al 2003;Turick, et al 2009). Similarly, dissimilatory metal reducing bacteria also are capable of using the pyomelanin they produce as a terminal electron acceptor (Turick, et al 2002).…”

“…This appears to only be the case of facultative anaerobes that experience daily fluctuations in oxygen levels. Pyomelanin production occurs during oxygen stress in the environment and may be a strategy to allow for increased electron transfer to inorganic terminal electron acceptors like Fe(III) oxides (Turick, et al 2003;Turick, et al 2009). Environmental concentrations of the precursors tyrosine or phenylalanine are likely sufficient in most locations to provide for enough pyomelanin production to significantly increase metal reduction rates (Turick, et al 2009).…”

“…Pyomelanin production occurs during oxygen stress in the environment and may be a strategy to allow for increased electron transfer to inorganic terminal electron acceptors like Fe(III) oxides (Turick, et al 2003;Turick, et al 2009). Environmental concentrations of the precursors tyrosine or phenylalanine are likely sufficient in most locations to provide for enough pyomelanin production to significantly increase metal reduction rates (Turick, et al 2009). However, pyomelanin production from cryptic growth also occurs in the absence of supplemental precursors in the laboratory (Turick, et al 2009).…”

“…Environmental concentrations of the precursors tyrosine or phenylalanine are likely sufficient in most locations to provide for enough pyomelanin production to significantly increase metal reduction rates (Turick, et al 2009). However, pyomelanin production from cryptic growth also occurs in the absence of supplemental precursors in the laboratory (Turick, et al 2009). Consequently, tyrosine or phenylalanine may not be required to be present in the environment for pyomelanin production to proceed, especially in biofilms where cell density is high.…”