title: Hydrogen-producing Escherichia coli strains overexpressing lactose permease: FT-IR analysis of the lactose-induced stress.
abstract: The lactose permease gene (lacY) was overexpressed in the septuple knockout mutant of Escherichia coli, previously engineered for hydrogen production from glucose. It was expected that raising the lactose transporter activity would elevate the intracellular lactose concentration, inactivate the lactose repressor, induce the lactose operon, and as a result stimulate overall lactose consumption and conversion. However, overexpression of the lactose transporter caused a considerable growth delay in the recombinant strain on lactose, resembling to some extent the "lactose killing" phenomenon. Therefore, the recombinant strain was subjected to selection on lactose-containing media. Selection on plates with 3% lactose yielded a strain with a decreased content of the recombinant plasmid but with an improved ability to grow and produce hydrogen on lactose. Macromolecular analysis of its biomass by means of Fourier transform-infrared spectroscopy demonstrated that increase of the cellular polysaccharide content might contribute to the adaptation of E. coli to lactose stress.
authors.affiliation: Institute of Microbiology and Biotechnology, University of Latvia, Riga, Latvia; Department of Water Engineering and Technology, Riga Technical University, Riga, Latvia.
authors.forename: Mara
authors.initials: M
authors.lastname: Grube
authors.forename: Ilze
authors.initials: I
authors.lastname: Dimanta
authors.forename: Marita
authors.initials: M
authors.lastname: Gavare
authors.forename: Inese
authors.initials: I
authors.lastname: Strazdina
authors.forename: Janis
authors.initials: J
authors.lastname: Liepins
authors.forename: Talis
authors.initials: T
authors.lastname: Juhna
authors.forename: Uldis
authors.initials: U
authors.lastname: Kalnenieks
mesh_terms: D004926:Escherichia coli / Q000201:enzymology; D015964:Gene Expression Regulation, Bacterial; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D017550:Spectroscopy, Fourier Transform Infrared; D013312:Stress, Physiological / Q000235:genetics*
chemical_list: D026901:Membrane Transport Proteins; D011135:Polysaccharides, Bacterial; D006859:Hydrogen; C021499:lactose permease; D007785:Lactose
keywords: Escherichia coli; FT-IR spectroscopy; biohydrogen fermentation; glycogen; lactose; lactose permease