This invention concerns a method for preparing a bacterial supernatant comprising culturing a cell of Pseudomonas environmental strain PF-11； and recovering the supernatant. This invention also concerns a method for reducing the amount of a biofilm on a surface, reducing adhesion of at least one organism to a surface, or reducing microfouling or macrofouling on a surface comprising contacting the surface with a supernatant, supernatant fraction, modified supernatant or modified supernatant fraction of Pseudomonas strain PF-11； or a composition comprising a supernatant, supernatant fraction, modified supernatant or modified supernatant fraction of Pseudomonas strain PF-11, and one or more acceptable carriers. This invention also concerns a method for killing or reducing the growth of a fungus or bacterial cell, or killing or inhibiting the development of an insect or marine copepod, comprising contacting the fungus, bacteria, insect or marine copepod with a supernatant, supernatant fraction, modified supernatant or modified supernatant fraction of a Pseudomonas strain PF-11 culture； or a composition comprising a supernatant, supernatant fraction, modified supernatant or modified supernatant fraction of a Pseudomonas strain PF-11 culture, and one or more acceptable carriers. This invention also concerns a substantially pure culture of Pseudomonas strain PF-11. This invention also concerns a culture that is enriched in Pseudomonas strain PF-11. This invention also provides a method of identifying whether a bacteria is capable of producing one or more extracellular proteases capable of digesting a high molecular weight substrate.Cette invention concerne un procédé de préparation d'un surnageant bactérien comprenant la culture d'une cellule de la souche environnementale PF-11 de Pseudomonas； et la récupération du surnageant. L'invention concerne également un procédé de réduction de la quantité de biofilm sur une surface, de réduction de l'adhérence d'au moins un organism
