Laurence Casalot

Effects of Hydrostatic Pressure on Growth and Luminescence of a Moderately-Piezophilic Luminous Bacteria Photobacterium phosphoreum ANT-2200

Bacterial bioluminescence is commonly found in the deep sea and depends on environmental conditions. Photobacterium phosphoreum ANT-2200 has been isolated from the NW Mediterranean Sea at 2200-m depth (in situ temperature of 13°C) close to the ANTARES neutrino telescope. The effects of hydrostatic pressure on its growth and luminescence have been investigated under controlled laboratory conditions, using a specifically developed high-pressure bioluminescence system. The growth rate and the maximum population density of the strain were determined at different temperatures (from 4 to 37°C) and pressures (from 0.1 to 40 MPa), using the logistic model to define these two growth parameters. Indeed, using the growth rate only, no optimal temperature and pressure could be determined. However, when both growth rate and maximum population density were jointly taken into account, a cross coefficient was calculated. By this way, the optimum growth conditions for P. phosphoreum ANT-2200 were found to be 30°C and, 10 MPa defining this strain as mesophile and moderately piezophile. Moreover, the ratio of unsaturated vs. saturated cellular fatty acids was found higher at 22 MPa, in agreement with previously described piezophile strains. P. phosphoreum ANT-2200 also appeared to respond to high pressure by forming cell aggregates. Its maximum population density was 1.2 times higher, with a similar growth rate, than at 0.1 MPa. Strain ANT-2200 grown at 22 MPa produced 3 times more bioluminescence. The proposed approach, mimicking, as close as possible, the in situ conditions, could help studying deep-sea bacterial bioluminescence and validating hypotheses concerning its role into the carbon cycle in the deep ocean.

Desulfovibrio tunisiensis sp. nov., a novel weakly halotolerant, sulfate-reducing bacterium isolated from exhaust water of a Tunisian oil refinery

A novel weakly halotolerant, sulfate-reducing bacterium, designated strain RB22(T), was isolated from exhaust water of a Tunisian oil refinery. Cells of strain RB22(T) were Gram-negative, motile, vibrio-shaped or sigmoid and non-spore-forming, and occurred singly or in chains. Strain RB22(T) grew between 15 and 45 degrees C (optimum, 37 degrees C) and at pH 4.5 to 9 (optimum, pH 7). NaCl was not required for growth, but the strain tolerated high NaCl concentrations (up to 70 g l(-1)) with an optimum of 40 g l(-1). Sulfate, thiosulfate, sulfite and elemental sulfur served as electron acceptors, but not fumarate. Nitrate and nitrite were not reduced. Strain RB22(T) utilized lactate, formate, fumarate, succinate, glycerol, H(2)+CO(2) and methanol as substrates. The DNA G+C content was found to be 59.6 mol%. Phylogenetic analysis based on the 16S rRNA gene revealed that the isolate was a member of the genus Desulfovibrio, with no close relatives at the species level (16S rRNA gene sequence similarity of less than 95 %). Strain RB22(T) exhibited levels of 16S rRNA gene sequence similarity of 94.6 and 94.12 % to the type strains of the closely related species Desulfovibrio aespoeensis and Desulfovibrio dechloracetivorans, respectively. On the basis of genotypic and phylogenetic characteristics, and significant phenotypic differences, we suggest that strain RB22(T) represents a novel species, for which the name Desulfovibrio tunisiensis sp. nov. is proposed. The type strain is RB22(T) (=NCIMB 14400(T)=JCM 15076(T)=DSM 19275(T)).

Biochemical, transcriptional and translational evidences of the phenol-meta-degradation pathway by the hyperthermophilic Sulfolobus solfataricus 98/2

Phenol is a widespread pollutant and a model molecule to study the biodegradation of monoaromatic compounds. After a first oxidation step leading to catechol in mesophilic and thermophilic microorganisms, two main routes have been identified depending on the cleavage of the aromatic ring: ortho involving a catechol 1,2 dioxygenase (C12D) and meta involving a catechol 2,3 dioxygenase (C23D). Our work aimed at elucidating the phenol-degradation pathway in the hyperthermophilic archaea Sulfolobus solfataricus 98/2. For this purpose, the strain was cultivated in a fermentor under different substrate and oxygenation conditions. Indeed, reducing dissolved-oxygen concentration allowed slowing down phenol catabolism (specific growth and phenol-consumption rates dropped 55% and 39%, respectively) and thus, evidencing intermediate accumulations in the broth. HPLC/Diode Array Detector and LC-MS analyses on culture samples at low dissolved-oxygen concentration (DOC  =  0.06 mg.L−1) suggested, apart for catechol, the presence of 2-hydroxymuconic acid, 4-oxalocrotonate and 4-hydroxy-2-oxovalerate, three intermediates of the meta route. RT-PCR analysis on oxygenase-coding genes of S. solfataricus 98/2 showed that the gene coding for the C23D was expressed only on phenol. In 2D-DIGE/MALDI-TOF analysis, the C23D was found and identified only on phenol. This set of results allowed us concluding that S. solfataricus 98/2 degrade phenol through the meta route.

Methanogenic Octadecene Degradation by Syntrophic Enrichment Culture from Brackish Sediments

A microbial enrichment culture from brackish sediments was able to grow on octadec-1-ene (an unsaturated aliphatic hydrocarbon) as sole source of carbon and energy, under methanogenic conditions. Octadecene degradation is stopped either when bromoethanesulfonic acid, a selective inhibitor of methanogenesis is introduced, or when hydrogen is introduced. In the presence of bromoethanesulfonic acid, the degradation is restored by the addition of a hydrogenotrophic sulfate-reducing microorganism with sulfate. Results of molecular biodiversity, which revealed the presence of bacteria as well as of acetoclastic and hydrogenotrophic methanogens, are consistent with a syntrophic degradation involving Bacteria and Archaea. This is the first demonstration of syntrophic alkene degradation by microbial communities, showing that syntrophy is more widespread than we could have thought so far. These results highlight the need for a better understanding of microbial interactions and their role in the organic-matter degradation in polluted environments.

Thermanaeromonas burensis sp. nov., a thermophilic anaerobe isolated from a subterranean clay environment.

A strictly anaerobic, thermophilic and halotolerant strain, designated IA106T, was isolated from the seepage water collected in a metal biocorrosion test at a depth of 490 m, in a 130-160 m thick, subterranean Callovo-Oxfordian clay formation (158-152 million years old) in northern France. This geological formation has been selected as the potential host rock for the French high-level nuclear waste repository. Cells of strain IA106T stained Gram-positive and were non-motile, spore-forming, straight rods (0.5 × 2-6 μm). The five major fatty acids were C16 : 0 (15.9 %), C18 : 0 (15.4 %), iso-C17 : 1 I and/or anteiso-C17 : 1 B(14.8 %), iso-C17 : 0 (14.7 %) and iso-C15 : 0 (13.0 %). Growth was observed at temperatures ranging from 55 to 70 °C and at pH 5.5-9. The salinity range for growth was 0-20 g NaCl 1- 1. Yeast extract was required for growth. Strain IA106T was able to grow on lactate and various sugars in the presence of thiosulfate as electron acceptor. Sulfate, sulfite, elemental sulfur, fumarate, nitrate and nitrite were not reduced. The DNA G+C content was 60.2 mol%. 16S rRNA gene sequence analysis indicated that strain IA106T belonged to the family Thermoanaerobacteraceae, class Clostridia, phylum Firmicutes, and was most closely related to Thermanaeromonas toyohensis DSM 14490T (95.16 % 16S rRNA gene sequence similarity). On the basis of 16S rRNA gene sequence comparisons and physiological characteristics, strain IA106T represents a novel species of the genus Thermanaeromonas, for which the name Thermanaeromonas burensis sp. nov. is proposed. The type strain is IA106T ( = DSM 26576T = JCM 18718T).

Mobilisporobacter senegalensis gen. nov., sp. nov., an anaerobic bacterium isolated from tropical shea cake.

A Gram-stain positive, endospore-forming, strictly anaerobic bacterium, designated strain Gal1T, was isolated from shea cake, a waste material from the production of shea butter, originating from Saraya, Senegal. The cells were rod-shaped, slightly curved, and motile with peritrichous flagella. The strain was oxidase-negative and catalase-negative. Growth was observed at temperatures ranging from 15 to 45 °C (optimum 30 °C) and at pH 6.5-9.3 (optimum pH 7.8). The salinity range for growth was 0-3.5 % NaCl (optimum 1 %). Yeast extract was required for growth. Strain Gal1T fermented various carbohydrates such as mannose, mannitol, arabinose, cellobiose, fructose, glucose, maltose, sucrose, trehalose and lactose and the major end-products were ethanol and acetate. The only major cellular fatty acid was C16 : 0 (19.6 %). The DNA base G+C content of strain Gal1T was 33.8 mol%. Analysis of the 16S rRNA gene sequence of the isolate indicated that this strain was related to Mobilitalea sibirica DSM 26468T with 94.27 % similarity, Clostridium populeti ATTC 35295T with 93.94 % similarity, and Clostridium aminovalericum DSM 1283T and Anaerosporobacter mobilis DSM 15930T with 93.63 % similarity. On the basis of phenotypic characteristics, phylogenetic analysis and the results of biochemical and physiological tests, strain Gal1T was clearly distinguished from closely related genera, and strain Gal1T can be assigned to a novel species of a new genus for which the name Mobilisporobacter senegalensis gen. nov., sp. nov. is proposed. The type strain is Gal1T ( = DSM 26537T = JCM 18753T).