Figure 6 Normalized absorption spectra of whole cell cultures during phototrophic and chemotrophic growth. The cell scattering was digitally subtracted in the spectra. (E) Nitrogen is assimilated during phototrophic and chemotrophic growth Biological nitrogen assimilation (i.e. diazotrophic growth) is an ancient process that Selleckchem ARN-509 is widely distributed in prokaryotes, and is found in some members of all groups of phototrophic bacteria . Previous studies showed that nitrogen assimilation in heliobacterial cultures is “”switched-off”" when NH4 + is supplied as the nitrogen source and activated with N2(g) supplied [6, 24], and that H. selleck inhibitor modesticaldum is one of
the only two known anaerobic anoxygenic phototrophs that can fix nitrogen at temperatures above 50°C [6, 7]. Significant amounts of chemical energy (16 ATP) and reducing PXD101 molecular weight power (8 Fdred) are required during diazotrophic growth (N2 + 8 H+ + 8 Fdred + 16 ATP → 2 NH3 + H2 + 8 Fdox + 16 ADP + 16 Pi) . In the energy metabolism of H. modesticaldum, ATP and reducing power
are required for carbon metabolism, nitrogen assimilation and hydrogen production. Because of the energy and reducing power demanded for nitrogen fixation, diazotrophic growth of H. modesticaldum in darkness may be very challenging. Figure 7 shows diazotrophic and non-diazotrophic growth during phototrophic and chemotrophic growth, and growth of H. modesticaldum is slower during diazotrophic growth. Table 3 indicates that a similar amount of acetate is excreted during diazotrophic and non-diazotrophic growth. Together, our Racecadotril studies suggest that H. modesticaldum generates sufficient chemical energy and reducing power for both carbon metabolism and nitrogen assimilation during chemotrophic growth. Figure 7 Cell growth with or without nitrogen fixation in pyruvate-grown cultures during phototrophic and chemotrophic growth. The cells were grown in the minimal medium with pyruvate as sole carbon
source and NH4 + or N2/H2 = 98/2 as the nitrogen source. Discussion D-sugars are photoassimilated by H. modesticaldum While the EMP pathway is annotated in the genome, no sugar-supported growth has been reported for H. modesticaldum. It is not uncommon for microorganisms that have the EMP pathway annotated but do not use glucose and other sugars as carbon sources, and to date only one heliobacterium, Heliobacterium gestii, has been reported to grow on C6-sugars, i.e. glucose and fructose . Alternatively, fermentation of glucose through the EMP pathway has been reported in non-phototrophic bacteria in the phylum Firmicutes [26, 27]. In this paper, we present the first report on the growth of H. modesticaldum supported by D-ribose, D-glucose and D-fructose with “”vitamin-level”" (0.02%) yeast extract included.