The present invention relates to the in vitro use of a cationic hydroxyalkyl guar for maintaining or increasing the growth rate of microorganisms, wherein said cationic hydroxyalkyl guar has an average molecular weight of between 2,000 Daltons and 90,000 Daltons.La présente invention concerne l'utilisation in vitro d'un guar hydroxyalkylé cationique pour maintenir ou augmenter le taux de croissance de microorganismes, ledit guar hydroxyalkylé cationique ayant un poids moléculaire moyen compris entre 2 000 Daltons et 90 000 Daltons.