Osmotically Induced Response in the Haloalkaliphilic "Halomonas pantelleriense"
Ida ROMANO, Barbara NICOLAUS*, Licia LAMA, Maria Cristina MANCA, and Agata GAMBACORTA
Instituto per la Chimica di Molecole di Interesse Biologico, C.N.R., Via Toiano 6,80072 Arco Felice, Napoli, Italy
From hard sand of the lake of Venere in the Pantelleria island (Sicily, Italy) was isolated and characterized a new bacterium, which on the basis' of physiological and genetic characteristics was classified as a new species of Halomonas genus, as "Halomonas pantelleriense"(1).
This bacterium is halotolerant and haloalkaliphilic, in fact, it required at least 1.5% of NaC1 for the growth with an optimum pH of 9.0 and an optimum salt requirement of 10%. In studying the properties of the haloalkaliphilic organisms is not possible to divorce the two stresses: salt and pH. Under different conditions the influence of salinity or alkalinity takes a different role(2). In order to explore biochemical features of osmoprotection, in H. pantelleriense, the accumulation of organic solutes in response to different conditions were examined by 13C NMR for the presence of organic solutes and their relative amounts were calculated by the integration of the carbonyl resonances in the expanded 13C NMR spectrum.
When H. pantelleriense was grown in the complex medium at different NaC1 concentrations (0.5-3.0 M) the compatible solutes were mainly glycine-betaine were the major compounds. At higher salt molarity glutamic acid was present only as a trace amount. At 1.0 M NaC1 concentration, glycine-betaine and ectoine were present in a quite similar amount. When H. pantelleriense was grown at 2 M NaC1 0H- ectoine was the most abundant coumpound, whereas at 3 M NaC1 concentration the glycine-betaine was the osmolyte found at higher concentration. When H. pantelleriense was grown at 0.5 M NaC1 in glucose-mineral medium the most abundant osmolytes were ectoine and glutamic acid, whereas glycine-betaine was a minor component, OH-ectoine was absent. Species related to H. pantelleriense, accumulated usually ectoine and hydroxyectoine in glucose-mineral medium, while in the complex medium they biosynthetized mainly betaine (3).
The results obtained for osmolyte biosynthesis in H. pantelleriense were in part consistent with the findings of Severin et al. (1992) (4), who demonstrated a low variability of solute patterns among chemoheterotrophic Proteobacteria with ectoine as the predominant solute.
The modulation of the lipid pattern under different growth conditions will be
