Laurent Verschuere
Ghent University
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Featured researches published by Laurent Verschuere.
Microbiology and Molecular Biology Reviews | 2000
Laurent Verschuere; Geert Rombaut; Patrick Sorgeloos; Willy Verstraete
SUMMARY There is an urgent need in aquaculture to develop microbial control strategies, since disease outbreaks are recognized as important constraints to aquaculture production and trade and since the development of antibiotic resistance has become a matter of growing concern. One of the alternatives to antimicrobials in disease control could be the use of probiotic bacteria as microbial control agents. This review describes the state of the art of probiotic research in the culture of fish, crustaceans, mollusks, and live food, with an evaluation of the results obtained so far. A new definition of probiotics, also applicable to aquatic environments, is proposed, and a detailed description is given of their possible modes of action, i.e., production of compounds that are inhibitory toward pathogens, competition with harmful microorganisms for nutrients and energy, competition with deleterious species for adhesion sites, enhancement of the immune response of the animal, improvement of water quality, and interaction with phytoplankton. A rationale is proposed for the multistep and multidisciplinary process required for the development of effective and safe probiotics for commercial application in aquaculture. Finally, directions for further research are discussed.
Applied and Environmental Microbiology | 2000
Laurent Verschuere; Hanglamong Heang; Godelieve Criel; Patrick Sorgeloos; Willy Verstraete
ABSTRACT In this study Vibrio proteolyticus CW8T2 has been identified as a virulent pathogen for Artemia spp. Its infection route has been visualized with transmission electron microscopy. The pathogen affected microvilli and gut epithelial cells, disrupted epithelial cell junctions, and reached the body cavity, where it devastated cells and tissues. In vivo antagonism tests showed that preemptive colonization of the culture water with nine selected bacterial strains protected Artemia juveniles against the pathogenic effects. Two categories of the selected strains could be distinguished: (i) strains providing total protection, as no mortality occurred 2 days after the experimental infection with V. proteolyticus CW8T2, with strain LVS8 as a representative, and (ii) strains providing partial protection, as significant but not total mortality was observed, with strain LVS2 as a representative. The growth of V. proteolyticus CW8T2 in the culture medium was slowed down in the presence of strains LVS2 and LVS8, but growth suppression was distinctly higher with LVS8 than with LVS2. It was striking that the strains that gave only partial protection against the pathogen in the in vivo antagonism test showed also a restricted capability to colonize the Artemia compared to the strains providing total protection. The in vivo antagonism tests and the filtrate experiments showed that probably no extracellular bacterial compounds were involved in the protective action but that the living cells were required to protect Artemia against V. proteolyticus CW8T2.
Journal of Applied Microbiology | 1997
Laurent Verschuere; Jean Dhont; Patrick Sorgeloos; Willy Verstraete
Artemia juveniles were cultured under intensive conditions in three series of six tanks at different times. Both plate counts and Biolog GN microtitre plates were used to monitor the microbial community. Repetitions of the Artemia cultures in time revealed significant differences in Biolog patterns and bacterial counts, showing that normal culture practices, including chlorination of the sea water, does not allow control of the associated microbial community. However, the similarity among the Biolog fingerprints of all 18 tanks as determined by the Pearson correlation coefficient was always high. Both observations together indicate that the microbial community which colonizes the culture tanks seems to be determined by both deterministic factors (e.g. salinity, temperature, oxygen concentration, composition of the feed) and stochastic factors (micro‐organisms still present in the sea water after chlorination, on the walls of the culture tanks or in the air around the culture tanks). When a high proportion of microbial r‐strategists was present in the water at the beginning of the Artemia culture, the smallest differences in Biolog patterns among the tanks of one series throughout the culture period were observed. A parallelism between Artemia rearing success, functional fingerprint of the bacterial community and the proportion of r‐strategists present, was observed. This suggests an important role of the bacterial community in the overall Artemia rearing success.
Aquaculture | 1999
Geert Rombaut; Ph. Dhert; J Vandenberghe; Laurent Verschuere; Patrick Sorgeloos; Willy Verstraete
Abstract The effect of bacterial strains on the growth rate of rotifers, Brachionus plicatilis , was determined under monoxenic conditions. The first objective was to obtain sterile rotifer cultures starting from rotifer resting eggs using merthiolate or glutaraldehyde as disinfectant. Sterile rotifer cultures were obtained, without affecting the hatching ability of the resting eggs, when 0.05 μl/l glutaraldehyde was used. This disinfection procedure was used to examine the effect of 20 bacterial strains, isolated from well-performing live-feed production systems, on the population growth rate of rotifers cultured under monoxenic conditions. Five out of the 20 bacterial strains tested were able to improve significantly the asexual reproduction of rotifers. The population growth rate ( μ pop ) of rotifer cultures treated with GR 12 and GR11 (respectively 0.664±0.043 and 0.622±0.062) was significantly higher than the μ pop of the control treatment (0.512±0.101). Overall, the egg ratio after 48 h was significantly higher in the cultures inoculated with the bacterial strains than in the axenic control treatment. The results show that it is possible to control the microbial community in rotifer cultures started from disinfected resting eggs by adding bacterial strains which have a positive effect on the population growth rate.
Systematic and Applied Microbiology | 1997
Ilse Kersters; Lieven Van Vooren; Laurent Verschuere; Luc Vauterin; Ann Wouters; Joris Mergaert; Jean Swings; Willy Verstraete
Summary The Biolog system was evaluated as a simple and rapid assay to characterize heterotrophic microbial communities. Factors influencing the substrate utilization profiles of microbial communities present in surface water and compost material were determined. Examination of five different production batches of Biolog GN microplates showed that the color development in the substrate response wells is significantly affected by the production batch. Although community Biolog profiles within the same production batch of GN microplates were reproducible, the color development in replicate control wells contained in Biolog MT microplates varied significantly. This implies that several substrate-free reference wells need to be inoculated with the same environmental sample to allow reliable data transformations of the 95 raw color responses in the GN microplates. Replicate suspensions of compost material could not be distinguished from each other using Biolog GN microplates originating from the same production batch, suggesting that the sample preparation procedure was highly reproducible. However, the data indicate that reliable use of the Biolog assay for the characterization of heterotrophic microbial communities is only possible by comparing samples of equivalent inoculum densities. Also, multiple readings over a time course of incubation are needed, to overcome the effect of nonlinear color development.
Water Air and Soil Pollution | 1998
Heidi Maricou; D Pereira; Laurent Verschuere; Sarah Philips; Willy Verstraete
Using an electronic nose, concentration ranges of volatile fatty acids(VFAs), methane and butane, NH3, HCl, SO2 andN2O have been measured to establish the relation between theconcentration in the liquid or the gas sample and the electronic nosereading. A quantitative sensorial odor perception (SOP) was introduced,based on the average reaction of the twelve available sensors of theelectronic nose. The results of the different compounds showed that thesensors reach a saturation level with increasing concentration. In the lowerconcentration ranges, linearity between concentration and signal outputoccurred. This linear interval was situated for the VFAs between thedetection limit in the range of 5 to 15 g dissolved compound per L distilledwater and the upper limit of 60 g L-1. For the gases, thedetection limit varied between 6 and 690 volumes of gas per million ofvolumes air (ppmv). The upper limit of the linear interval ranged from 100–3000 ppmv depending on the compound. For the olfactometry reference product n-butanol, with a reported olfactory lower threshold valueof 0.04 ppmv, the electronic nose was less sensitive and gave a detectionlimit around 975 ppmv. The different compounds could be visualized in radarplots, which had a specific profile for each compound. The higher theconcentration of the volatile compounds in the air, the larger the surfaceof the respective radarplot. A discriminant analysis showed clusters ofcompounds such as the VFAs, the non polar gaseous compounds methane andbutane and the other more polar gaseous compounds.
Systematic and Applied Microbiology | 1998
Laurent Verschuere; Veerle Fievez; Lieven Van Vooren; Geert Rombaut; Willy Verstraete
Summary The color development curves obtained from multiple readings of Biolog GN microtiter plates over a long incubation time were fitted to the Gompertz function. This yielded — for each sole-carbon source — the incubation time independent and biologically relevant Gompertz parameters A (maximal extent of color development), μ M (specific color development rate) and λ (lagtime). To evaluate the applicability of the model, the coefficients of determination, the residuals, the biological significance of the parameters, the stability of the parameter estimates and the predicting power of the model were determined. For the pure strains Vibrio alginolyticus and Pseudomonas fluorescens the model passed all the criteria. For the model community consisting of a mixture of 9 strains, all criteria were met for almost all the oxidized carbon sources. However, a high amount of measuring points in the color development curve is necessary (preferably >20) and the reading frequency needs to be the highest in the lagphase and the exponential phase to ensure a high stability and predictability of the estimates of μ M and λ, especially when the color develops very rapidly in the wells. For a few carbon sources the Gompertz model was not appropriate, as the color development curve showed clearly 2 tiers. However, it is substantiated that the second tier may be eliminated from the time series, which allowed the model again to pass all the criteria. Finally, comparison of Biolog fingerprints of environmental samples was made with principal component analysis of the estimated Gompertz parameters for each carbon source. It is shown that this approach is practicable and may yield consistent results for environmental microbial community analysis.
Applied and Environmental Microbiology | 1999
Saïd El Fantroussi; Laurent Verschuere; Willy Verstraete; Eva M. Top
Applied and Environmental Microbiology | 1999
Laurent Verschuere; Geert Rombaut; Geert Huys; Jean Dhont; Patrick Sorgeloos; Willy Verstraete
Water Environment Research | 1997
Krist V. Gernaey; Laurent Verschuere; Leen Luyten; Willy Verstraete