Article

Abstract

-Immobilization of lactococci. Bacteria present in dairy products exist predominantly in an immobilized form, as coagulated milk is not a liquid and thus does not allow bacteria to move free. Lactococci may be immobilized by attachment to surfaces, chain formation and by trapping in the extracellular matrix. Use of semi-liquid medium to simulate immobilized growth revealed characteristic properties of non-planctonic lactococcal cultures, which are: limited distribution in the medium, slow growth, a mixture of the stationary and exponentially growing cells, and genetic instability of the culture. These characteristics depend on molecular composition of the cell wall. We have shown that peptidoglycan (PG) breaks, which can be introduced not only by PG hydrolases, but also by defects of PG synthesis machinery (mutation in the ponA gene) play a significant role in immobilization (adhesion, sedimentation, chain formation). We also showed that cell wall anchored proteins play a positive role in L. lactis adhesion. Our studies contribute to the identification of molecular determinants responsible for the phenomenon of adhesion, formation of biofilms, and more generally for functioning of the lactic acid bacteria in natural and industrial environments. They have equally as objective to define the molecular factors necessary for the establishment of positive biofilms, which would minimize the risks of contamination in dairy industry. Lactococcus lactis / adhesion / biofilm / cell wall / peptidoglycan hydrolaseRésumé -Dans l'industrie laitière, les bactéries se retrouvent la plupart du temps sous une forme immobilisée, dans la mesure où le lait coagulé ne constitue pas un milieu liquide et ne permet donc pas aux bactéries en croissance des déplacements libres. Notre principal objectif réside dans la modélisation de la croissance immobilisée. Les lactocoques peuvent être immobilisés par un attachement sur les surfaces, la formation de chaînes ou l'emprisonnement au sein d'une matrice extra cellulaire. L'utilisation d'un milieu semi-liquide comme modèle d'immobilisation nous a permis de montrer que les propriétés caractéristiques de la croissance non-planctonique des lactocoques consistent en une distribution limitée dans le milieu, une croissance lente et le mélange de cellules en phases stationnaires et exponentielles, et que l'immobilisation est à l'origine de l'instabilité génétique de la culture. Ces caractéristiques dépendent de la composition moléculaire de la paroi cellulaire. Les cassures de peptidoglycane (PG), qui peuvent être introduites non seulement par des PG hydrolases, mais aussi suite à des défauts de la machinerie de synthèse du PG (mutation du gène ponA), sont importantes dans la croissance sous forme immobilisée des * Auteur correspondant : Saulius.Kulakauskas@diamant.jouy.inra.fr 104 M. Ibrahim et al.

Preparation of a biosorbent complex (clay particles/Streptococcus thermophilus) to treat polluted water with methylene blue

“…Application to experimental results, kinetic models, Lagergren (1st order), Ho and Mc Kay (2nd order) and Weber and Morris (intra-particular diffusion), in their linear forms, Eq. (5), (6) and 7respectively [2], shows good representativeness of the kinetic model of Ho and Mc Kay for the experimental values found, as shown in Fig. 6, with a good correlation coefficient R 2 and a small relative error ε (%) (Eq.…”

“…For this, several steps are necessary where physical, chemical and biological processes are involved [5]. Bacterial growth under natural conditions is mainly in the form of immobilized communities (films, colonies or aggregates) and their activity is often studied from isolated planktonic cells [6].…”

Genetic Features of Resident Biofilms Determine Attachment of Listeria monocytogenes

“…Chain formation has been described in other bacterial models as a means of developing cohesive 3D biofilms without extensive matrix formation (51). A previous study conducted under static conditions had also indicated that the ⌬acmA mutant was a poor producer of biofilms compared to the WT (32,42). As observed in other bacterial models (50,65), extracellular DNA is thus one of the principal components of the L. lactis biofilm matrix.…”

Over-production of exopolysaccharide by Lacticaseibacillus rhamnosus CNCM I-3690 strain cutbacks its beneficial effect on the host

“…Under these conditions, viscosity of SL medium restricts free movements of bacteria and sedimentation represents the principal means of displacement for bacteria which do not displays autonomous motility properties. When starting form a colony of a non-EPS-producing strain in SL www.nature.com/scientificreports/ medium, simultaneous growth and sedimentation result in a streaked colony 21,33 . Contrariwise, EPS-producing bacteria in these conditions are trapped in extracellular agar matrix by produced EPS and do not sediment, consequently forming round colonies.…”