AUTHOR=Moore Eli K., Hopmans Ellen C., Rijpstra W. Irene C., Sanchez Andrea Irene , Villanueva Laura , Wienk Hans , Schoutsen Frans , Stams Alfons , Sinninghe Damste Jaap 

TITLE=Lysine and novel hydroxylysine lipids in soil bacteria: amino acid membrane lipid response to temperature and pH in Pseudopedobacter saltans

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00637

DOI=10.3389/fmicb.2015.00637

ISSN=1664-302X

ABSTRACT=<p>Microbial decomposition of organic matter is an essential process in the global carbon cycle. The soil bacteria <italic>Pseudopedobacter saltans</italic> and <italic>Flavobacterium johnsoniae</italic> are both able to degrade complex organic molecules, but it is not fully known how their membrane structures are adapted to their environmental niche. The membrane lipids of these species were extracted and analyzed using high performance liquid chromatography-electrospray ionization/ion trap/mass spectrometry (HPLC-ESI/IT/MS) and high resolution accurate mass/mass spectrometry (HRAM/MS). Abundant unknown intact polar lipids (IPLs) from <italic>P. saltans</italic> were isolated and further characterized using amino acid analysis and two dimensional nuclear magnetic resonance (NMR) spectroscopy. Ornithine IPLs (OLs) with variable (hydroxy) fatty acid composition were observed in both bacterial species. Lysine-containing IPLs (LLs) were also detected in both species and were characterized here for the first time using HPLC-MS. Novel LLs containing hydroxy fatty acids and novel hydroxylysine lipids with variable (hydroxy) fatty acid composition were identified in <italic>P. saltans</italic>. The confirmation of OL and LL formation in <italic>F. johnsoniae</italic> and <italic>P. saltans</italic> and the presence of <italic>Ols</italic>F putative homologs in <italic>P. saltans</italic> suggest the <italic>Ols</italic>F gene coding protein is possibly involved in OL and LL biosynthesis in both species, however, potential pathways of OL and LL hydroxylation in <italic>P. saltans</italic> are still undetermined. Triplicate cultures of <italic>P. saltans</italic> were grown at three temperature/pH combinations: 30°C/pH 7, 15°C/pH 7, and 15°C/pH 9. The fractional abundance of total amino acid containing IPLs containing hydroxylated fatty acids was significantly higher at higher temperature, and the fractional abundance of lysine-containing IPLs was significantly higher at lower temperature and higher pH. These results suggest that these amino acid-containing IPLs, including the novel hydroxylysine lipids, could be involved in temperature and pH stress response of soil bacteria.</p>