Abstract
As genes for type II fatty acid synthesis are essential to the growth of Escherichia coli, its sole (anaerobic) pathway has significant potential as a target for novel antibacterial drug, and has been extensively studied. Despite this, we still know surprisingly little about fatty acid synthesis in bacteria because this anaerobic pathway in fact is not widely distributed. In this study, we show a novel model of unsaturated fatty acid (UFA) synthesis in Shewanella, emerging human pathogens in addition to well-known metal reducers. We identify both anaerobic and aerobic UFA biosynthesis pathways in the representative species, S. oneidensis. Uniquely, the bacterium also contains two regulators FabR and FadR, whose counterparts in other bacteria control the anaerobic pathway. However, we show that in S. oneidensis these two regulators are involved in regulation of both pathways, in either direct or indirect manner. Overall, our results indicate that the UFA biosynthesis and its regulation are far more complex than previously expected, and S. oneidensis serves as a good research model for further work.
Highlights
Bacterial membrane, an essential structure involved in almost every aspect of bacterial growth and metabolism, generally lacks sterols and contains mainly phospholipids such as phosphatidylethanolamine (PtdEtn) and phosphatidylglycerol (PtdGro) (Zhang and Rock, 2008)
ONEIDENSIS POSSESSES BOTH ANAEROBIC AND AEROBIC unsaturated fatty acid (UFA) BIOSYNTHESIS PATHWAYS According to the genome annotation, S. oneidensis has the fabASo (SO1856) gene (Heidelberg et al, 2002), whose protein product shares up to 67% of sequence identity with FabAEc from E. coli
To control the production of a variety of fatty acids with different melting temperatures to achieve the proper physical state of the membrane phospholipids, the saturated fatty acids (SFAs), UFA, and branched-chain fatty acids (BCFAs) biosynthesis pathways must be strictly regulated according to the availability of fatty acids (Zhang and Rock, 2008)
Summary
An essential structure involved in almost every aspect of bacterial growth and metabolism, generally lacks sterols and contains mainly phospholipids such as phosphatidylethanolamine (PtdEtn) and phosphatidylglycerol (PtdGro) (Zhang and Rock, 2008). To support normal structure and functions, membranes are required to maintain the appropriate fluidity, which is determined largely by the composition of fatty acids attached to membrane phospholipids, including straight-chain unsaturated fatty acids (UFAs), saturated fatty acids (SFAs), and branched-chain fatty acids (BCFAs) (Campbell and Cronan, 2001; Mendoza, 2014). As these fatty acids are required for bacterial survival, their biosynthesis pathway has been an important target for the development of novel antimicrobials in recent years, even though microbes are capable of incorporating environmental fatty acids into phospholipids (Campbell and Cronan, 2001; Parsons and Rock, 2011). While bacteria in which the subject has been investigated so far are generally equipped with either pathway for UFA biosynthesis, Pseudomonas aeruginosa has both, with two independent desaturases DesA and DesB (Zhu et al, 2006)
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