Enrico Esposito

Effects of temperature on ether lipid composition of Caldariella acidophila

The composition of the ether lipids of a strain of Caldariella acidophila, with respect to the different numbers of cyclizations of the biphytanyl components, is shown to differ between the various complex lipid classes, but the degree of cyclization increases systematically with the growth temperature in the range 75–89°. The problem of distinguishing adaptive from phyletic features in archaebacterial lipids is considered.

“Bacillus thermoantarcticus” sp. nov., from Mount Melbourne, Antarctica: a novel thermophilic species

Abstract A novel thermophilic Gram-positive bacillus, “Bacillus thermoantarcticus”, isolated from geothermal soil near the crater of Mount Melbourne, is described. The organism grows at an optimal temperature of 63°C at pH 6.0, is oxidase-positive, catalase-negative and produces an exopolysaccharide, an exocellular xylanase, an intracellular alcohol dehydrogenase and exo- and endocellular α-glucosidase(s). The sequence of 16S rDNA is very similar to that of “Bacillus thermoglucosidasius”; however, the guanine-plus-cytosine (G+C) content is 8 mol% higher. The type strain is “Bacillus thermoantarcticus” (DSM 9572).

Alicyclobacilli from an unexplored geothermal soil in Antarctica: Mount Rittmann

Abstract The isolation of three species from soil samples from an unexplored site in Antarctica, belonging to the Alicyclobacillus genus, is reported. The isolates, named MR1, MR2 and MR4, were from 30 samples of geothermal soil from Mount Rittmann. All the isolates had lipids based mainly on fatty acids possessing a terminal cyclohexane; hopanoid and quinones of MK-7 were also present. All isolates were characterized by phenotypic features and the isolate MR1 was subjected to genetic analyses. The isolates were thermoacidophilic, showing an optimum temperature of 63°C and an optimum pH of 3.5–4.0. They were able to grow in the temperature range 45–70°C. The percentage C+G of DNA of MR1 was 64.9% and showed a 16S rDNA similarity of 99.3% with Alicyclobacillus acidocaldarius ATCC 43034 and a DNA-DNA homology of 69.7% with A. acidocaldarius DSM 446. The strain MR1 is unable to produce amylolytic activity under different growth conditions. It is proposed to accommodate MR1 in the genus Alicyclobacillus as subspecies rittmannii of A. acidocaldarius.

Haloarcula spp able to biosynthesize exo- and endopolymers

Three halobacteria strains (T5, T6, T7), growing optimally at a sodium chloride concentration of 3.5 M, were isolated from samples collected in the Tunisian marine saltern located close to Monastir. Although they were different in colony and cell morphology, the isolates were similar in most respects and all produced a homopolyester identified spectroscopically as polyhydroxybutyrate when grown on carbohydrates. Under the same conditions, the isolates formed acidic exopolysaccharides. Acid methanolysis of their complex lipids released archaeol (2,3-di-O-phytanyl-sn-glycerol). All the isolates had polar lipid patterns characteristic of representatives of the genus Haloarcula. Partial sequence analysis of 16S rRNA genes from strain T5 confirmed its assignment to the genus Haloarcula. Although strain T5 differed phenotypically from the species Haloarcula japonica in several respects, DNA–DNA hybridization indicated that the T5 isolate is a new strain of H. japonica.

Lipid modulation by environmental stresses in two models of extremophiles isolated from Antarctica

Abstract Thermoacidophilic and halotolerant microorganisms from the Antarctic continent were studied for their lipid modulation under stress growth conditions. Temperature-induced changes in complex lipids and fatty acids of four strains belonging to the genus Alicyclobacillus involved the relative proportions of different polar lipids and the synthesis of ω-cyclohexyl-acyl chains, which were favoured by high temperatures. Studies were carried out on the lipid composition of four strains of extremely halotolerant bacteria belonging to the genus Micrococcus grown at different salt concentrations from 0 up to 4.5 M NaCl. The main lipids found were two unidentified glycolipids and two phospholipids: 1,2 diacylglycero-3-phosphoryl-glycerol (PG) and cardiolipin (DPG). Among the strains analysed, the lipids of the Micrococcus strain Erebus were shown to be strongly influenced by salt concentrations, in that DPG and one glycolipid were absent at a low salt molarity while, under these conditions, PG was the main lipid found. The predominant fatty acids in all halotolerant strains were of the anteiso type; growth under increasing salinity gave rise to an increase in long chain fatty acids and of straight chain fatty acids, while a decrease in iso fatty acids occurred.

Exopolysaccharide production by a new Halomonas strain CRSS isolated from saline lake Cape Russell in Antarctica growing on complex and defined media

A haloalkalophilic Halomonas strain CRSS, isolated from salt sediments in Antarctica, produced exocellular polysaccharides (EPS) up to 2.9gg-1 dry cells. Acetate was the most efficient carbon source for EPS production. The composition of media strongly affected the nature of the polymers; a mannan and a xylo-mannan, were obtained when cells were grown on complex media. Acetate was the most efficient carbon source for EPS production and in presence of this substrate, a new polysaccharide, a fructo-glucan, was produced. The EPS fraction was composed by glucose, fructose, glucosamine and galactosamine in relative proportions of 1:0.7:0.3:trace.

Effects of growth temperature on the polar lipid pattern and fatty acid composition of seven thermophilic isolates from the Antarctic Continent

Summary Seven thermophilic strains isolated from different geographical areas of the Antarctic Continent were examined for their polar lipid pattern and fatty acid composition. Temperature induced changes in membrane lipids were also analysed. They involved the relative proportions of different polar lipids and the synthesis of higher melting point fatty acids, which was favoured by high temperatures. Taxonomic implications on the basis of fatty acid analysis were reported.

Isolation of five strains of thermophilic eubacteria in Antarctica

SummaryFive isolates of thermophilic bacteria, capable of growing at 65°C, were obtained from samples of soil collected from the Cryptogam Ridge (Mount Melbourne) and in the area north of Edmonson Point, Northern Victoria Land, Antarctica. Electron microscopy, morphological and physiological properties, lipid analyses and GC content of the isolates are described in this paper. On the basis of the results presented the organisms belong to the eubacterial domain.

Extremophiles in Antarctica

Abstract Isolation and classification of extremophiles and cyanobacteria are described. Seven thermophiles, belonging to Bacillus genus, five acidothermophiles, classified as Alicyclobacillus, and five halotolerant cocci, belonging to Micrococcus genus, were isolated from Antarctic samples of geothermal and saline soils. The isolates were examined for their polar lipid and fatty acid composition. Changes in membrane lipids, induced by stressed growth conditions, were analysed. The isolation of two new cyanobacteria and their polysaccharide characterization were described. The exopolysaccharide production and characterization, as well as thermophilic xylan‐degrading enzymes, were studied.