Characterization of exopolysaccharides produced by three moderately halophilic bacteria belonging to the family Alteromonadaceae

Halomonas stenophila sp. nov., a halophilic bacterium that produces sulphate exopolysaccharides with biological activity

We have undertaken a polyphasic taxonomic study of two halophilic, Gram-negative bacterial strains, N12T and B-100, that produce sulphated exopolysaccharides with biological activity. They were isolated from two different saline soil samples. Both strains grow at NaCl concentrations within the range 3–15 % (w/v) [optimum 5–10 % (w/v)], at 15–37 °C (optimum 20–32 °C) and at pH 6–8 (optimum pH 7–8). Their 16S rRNA gene sequences indicate that they belong to the genus Halomonas in the class Gammaproteobacteria. Their closest relative is Halomonas nitroreducens, to which our strains show maximum 16S rRNA gene sequence similarity values of 98.7 % (N12T) and 98.3 % (B-100). Their DNA G+C contents are 61.9 and 63.8 mol%, respectively. The results of DNA–DNA hybridizations showed 43.9 % relatedness between strain N12T and H. nitroreducens CECT 7281T, 30.5 % between N12T and Halomonas ventosae CECT 5797T, 39.2 % between N12T and Halomonas fontilapidosi CECT 7341T, 46.3 % between N12T and Halomonas maura CECT 5298T, 52.9 % between N12T and Halomonas saccharevitans LMG 23976T, 51.3 % between N12T and Halomonas koreensis JCM 12237T and 100 % between strains N12T and B-100. The major fatty acids of strain N12T are C12 : 0 3-OH (5.42 %), C15 : 0 iso 2-OH/C16 : 1ω7c (17.37 %), C16 : 0 (21.62 %) and C18 : 1ω7c (49.19 %). The proposed name for the novel species is Halomonas stenophila sp. nov. Strain N12T ( = CECT 7744T  = LMG 25812T) is the type strain.

An exopolysaccharide produced by the novel halophilic bacterium Halomonas stenophila strain B100 selectively induces apoptosis in human T leukaemia cells

Microbial exopolysaccharides (EPSs) are highly heterogeneous polymers produced by fungi and bacteria and have recently been attracting considerable attention from biotechnologists because of their potential applications in many fields, including biomedicine. We have screened the antitumoural activity of a panel of sulphated EPSs produced by a newly discovered species of halophilic bacteria. We found that the novel halophilic bacterium Halomonas stenophila strain B100 produced a heteropolysaccharide that, when oversulphated, exerted antitumoural activity on T cell lines deriving from acute lymphoblastic leukaemia (ALL). Only tumour cells were susceptible to apoptosis induced by the sulphated EPS (B100S), whilst primary T cells were resistant. Moreover, freshly isolated primary cells from the blood of patients with ALL were also susceptible to B100S-induced apoptosis. The newly discovered B100S is therefore the first bacterial EPS that has been demonstrated to exert a potent and selective pro-apoptotic effect on T leukaemia cells, and thus, we propose that the search for new antineoplastic drugs should include the screening of other bacterial EPSs, particularly those isolated from halophiles.

Characterization of the exopolysaccharide produced by Salipiger mucosus A3, a halophilic species belonging to the Alphaproteobacteria, isolated on the Spanish Mediterranean seaboard

We have studied the exopolysaccharide produced by the type strain of Salipiger mucosus, a species of halophilic, EPS-producing (exopolysaccharide-producing) bacterium belonging to the Alphaproteobacteria. The strain, isolated on the Mediterranean seaboard, produced a polysaccharide, mainly during its exponential growth phase but also to a lesser extent during the stationary phase. Culture parameters influenced bacterial growth and EPS production. Yield was always directly related to the quantity of biomass in the culture. The polymer is a heteropolysaccharide with a molecular mass of 250 kDa and its components are glucose (19.7%, w/w), mannose (34%, w/w), galactose (32.9%, w/w) and fucose (13.4%, w/w). Fucose and fucose-rich oligosaccharides have applications in the fields of medicine and cosmetics. The chemical or enzymatic hydrolysis of fucose-rich polysaccharides offers a new efficient way to process fucose. The exopolysaccharide in question produces a solution of very low viscosity that shows pseudoplastic behavior and emulsifying activity on several hydrophobic substrates. It also has a high capacity for binding cations and incorporating considerable quantities of sulfates, this latter feature being very unusual in bacterial polysaccharides.

Calcium carbonate precipitation by cyanobacterial polysaccharides

Cyanobacteria have been recognized as key players in the precipitation of calcium carbonate in marine and freshwater systems. These bacteria increase pH, (as a result of photosynthetic activity) and also produce extracellular polysaccharides, which act as binding sites for Ca2+ and CO32−. Both processes influence the morphology and the mineralogy of the carbonate minerals. In order to clarify the role of polysaccharides of picocyanobacteria upon calcium carbonate precipitation, both their buffering capacity and ability to induce precipitation need to be investigated. In this experimental study, we characterized the polysaccharides of three unicellular autotrophic picocyanobacterial Synechococcus-type strains by potentiometric titration and infrared spectroscopy. Potentiometric titrations were conducted to determine the total buffering capacity. The nature and concentration of active sites of the polysaccharides was clarified with the aid of potentiometric titration and spectral analysis of an aqueous cellular suspension. Precipitation experiments with polysaccharides of different strains allowed an estimation of their potential to precipitate calcium carbonate. The results presented here indicate that polysaccharides from cyanobacteria have a strong potential to exchange protons with their surrounding environment. Precipitation experiments demonstrated that extracellular polysaccharides of all the strains studied able to precipitate calcium carbonate.

Characterization of extracellular polymeric substances from acidophilic microbial biofilms

We examined the chemical composition of extracellular polymeric substances (EPS) extracted from two natural microbial pellicle biofilms growing on acid mine drainage (AMD) solutions. The EPS obtained from a mid-developmental-stage biofilm (DS1) and a mature biofilm (DS2) were qualitatively and quantitatively compared. More than twice as much EPS was derived from DS2 as from DS1 (approximately 340 and 150 mg of EPS per g [dry weight] for DS2 and DS1, respectively). Composition analyses indicated the presence of carbohydrates, metals, proteins, and minor quantities of DNA and lipids, although the relative concentrations of these components were different for the two EPS samples. EPS from DS2 contained higher concentrations of metals and carbohydrates than EPS from DS1. Fe was the most abundant metal in both samples, accounting for about 73% of the total metal content, followed by Al, Mg, and Zn. The relative concentration profile for these metals resembled that for the AMD solution in which the biofilms grew, except for Si, Mn, and Co. Glycosyl composition analysis indicated that both EPS samples were composed primarily of galactose, glucose, heptose, rhamnose, and mannose, while the relative amounts of individual sugars were substantially different in DS1 and DS2. Additionally, carbohydrate linkage analysis revealed multiply linked heptose, galactose, glucose, mannose, and rhamnose, with some of the glucose in a 4-linked form. These results indicate that the biochemical composition of the EPS from these acidic biofilms is dependent on maturity and is controlled by the microbial communities, as well as the local geochemical environment.