Emmanuel Rondags

CTAB turbidimetric method for assaying hyaluronic acid in complex environments and under cross-linked form

The cetyltrimethylammonium bromide turbidimetric method (CTM) has been developed to quantify the hyaluronic acid (HA) in complex media to overcome the lack of selectivity and specificity of the standard carbazole method. The objective of this work is to assess the potential application of CTM to determine HA concentration. Factors such as duration of incubation, linearity range, HA size and form (natural linear HA or cross linked HA), pH and ionic environment impact were investigated. The incubation time was set to 10 min and the calibration curve was linear up to 0.6 g L(-1). The quantitative method was relevant whatever the HA size and form, and also for a wide range of conditions. The robustness of the CTM added to its high specificity and simplicity demonstrated that the CTM is a valuable method that would be an interesting substitute to the carbazole assay for HA quantification.

Kinetic study of the chemical reactivity of α-acetolactate as a function of pH in water, and in fresh and fermented culture media used for Lactococcus lactis spp. Lactis bv. diacetylactis cultivation

SummarySpontaneous oxidative decarboxylation of α-acetolactic acid (ALA) to diacetyl has been assessed under anaerobiosis as a function of pH in water, and in fresh and filtered Lactococcus lactis spp. lactis bv. diacetylactis SD 933 fermented culture media. Whatever the reaction medium, ALA was shown to be potentially reactive, depending on the pH of medium. Diacetyl production mechanism by this strain is discussed on the basis of these kinetic data.

Recombinant pediocin in Lactococcus lactis : increased production by propeptide fusion and improved potency by co-production with PedC

We describe the impact of two propeptides and PedC on the production yield and the potency of recombinant pediocins produced in Lactococcus lactis. On the one hand, the sequences encoding the propeptides SD or LEISSTCDA were inserted between the sequence encoding the signal peptide of Usp45 and the structural gene of the mature pediocin PA‐1. On the other hand, the putative thiol‐disulfide oxidoreductase PedC was coexpressed with pediocin. The concentration of recombinant pediocins produced in supernatants was determined by enzyme‐linked immunosorbent assay. The potency of recombinant pediocins was investigated by measuring the minimal inhibitory concentration by agar well diffusion assay. The results show that propeptides SD or LEISSTCDA lead to an improved secretion of recombinant pediocins with apparently no effect on the antibacterial potency and that PedC increases the potency of recombinant pediocin. To our knowledge, this study reveals for the first time that pediocin tolerates fusions at the N‐terminal end. Furthermore, it reveals that only expressing the pediocin structural gene in a heterologous host is not sufficient to get an optimal potency and requires the accessory protein PedC. In addition, it can be speculated that PedC catalyses the correct formation of disulfide bonds in pediocin.

Quantification of extracellular α-acetolactate oxidative decarboxylation in diacetyl production by an α-acetolactate overproducing strain of Lactococcus lactis sp. lactis bv. diacetylactis

The quantification of α-acetolactate (AAL) extracellular oxidative decarboxylation during an AAL overproducing strain culture shows that this reaction is at the origin of about 90% of the diacetyl production and that only a small proportion of extracellular AAL is readily transformed to diacetyl. These results, compared with previous ones obtained with a non AAL accumulating strain, allow research options to be put forward for the improvement of microbiological diacetyl production.

Diauxic growth of Clostridium acetobutylicum ATCC 824 when grown on mixtures of glucose and cellobiose

Clostridium acetobutylicum, a promising organism for biomass transformation, has the capacity to utilize a wide variety of carbon sources. During pre-treatments of (ligno) cellulose through thermic and/or enzymatic processes, complex mixtures of oligo saccharides with beta 1,4-glycosidic bonds can be produced. In this paper, the capability of C. acetobutylicum to ferment glucose and cellobiose, alone and in mixtures was studied. Kinetic studies indicated that a diauxic growth occurs when both glucose and cellobiose are present in the medium. In mixtures, d-glucose is the preferred substrate even if cells were pre grown with cellobiose as the substrate. After the complete consumption of glucose, the growth kinetics exhibits an adaptation time, of few hours, before to be able to use cellobiose. Because of this diauxic phenomenon, the nature of the carbon source deriving from a cellulose hydrolysis pre-treatment could strongly influence the kinetic performances of a fermentation process with C. acetobutylicum.