Geneviève Gaudet

Recent developments in microbial oils production: a possible alternative to vegetable oils for biodiesel without competition with human food?

Since centuries vegetable oils are consumed as human food but it also finds applications in biodiesel production which is attracting more attention. But due to being in competition with food it could not be sustainable and leads the need to search for alternative. Nowdays microbes-derived oils (single cell oils) seem to be alternatives for biodiesel production due to their similar composition to that of vegetable oils. However, the cold flow properties of the biodiesel produced from microbial oils are unacceptable and have to be modified by an efficient transesterification. Glycerol which is by product of transesterification can be valorised into some more useful products so that it can also be utilised along with biodiesel to simplify the downstream processing. The review paper discusses about various potent microorganisms for biodiesel production, enzymes involved in the lipid accumulation, lipid quantification methods, catalysts used in transesterification (including enzymatic catalyst) and valorisation of glycerol.

Re-investigation of glucose metabolism in Fibrobacter succinogenes, using NMR spectroscopy and enzymatic assays. Evidence for pentose phosphates phosphoketolase and pyruvate formate lyase activities.

The glucose metabolism of Fibrobacter succinogenes S85 was studied in detail; key intermediates and alternative pathways were evidenced by NMR and/or enzymatic assays. A high phosphoketolase activity was detected in four strains of Fibrobacter under strictly anaerobic conditions, with ribose-5-phosphate as substrate, no activity was evidenced with fructose-6-phosphate. This is the first report of a pentose phosphates phosphoketolase in bacteria unable to use pentoses. In contrast, the Entner-Doudoroff pathway and the oxidative branch of the pentose phosphate pathway could not be evidenced. Incubation of living cells of F. succinogenes with Na2(13)CO3 confirmed the incorporation of 13CO2 in the carboxylic group of succinate. The presence of fumarase was evidenced by in vivo 4C-NMR using 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO): the enzyme showed a high reversibility under physiological conditions. The production of formate from glucose catabolism was evidenced by enzymatic assay and by NMR and a pyruvate formate lyase activity was detected using strictly anaerobic conditions.

In vivo 23Na nuclear magnetic resonance study of maintenance of a sodium gradient in the ruminal bacterium Fibrobacter succinogenes S85

ABSTRACT Sodium gradients (ΔpNa) were measured in resting cells ofFibrobacter succinogenes by in vivo 23Na nuclear magnetic resonance using Tm(DOTP)5−[thulium(III) 1,4,7,10-tetraazacyclododecane-N′,N′′,N′′′-tetramethylenephosphonate] as the shift reagent. This bacterium was able to maintain a ΔpNa of −55 to −40 mV for extracellular sodium concentrations ranging from 30 to 200 mM. Depletion of Na+ ions during the washing steps led to irreversible damage (modification of glucose metabolism and inability to maintain a sodium gradient).