Choanoflagellates are single-celled eukaryotes that feed on bacteria. In the presence of their food bacteria, some choanoflagellates develop multicellular structures in which the individual choanoflagellate cells are attached to one another. Based on this observation, it may be assumed that:

Choanoflagellates, a group of microbial eukaryotes that are the nearest living family members of creatures, guarantee to help light up the components by which microscopic organisms impact creature improvement.
As did cells in the main creatures, choanoflagellates utilize a particular neckline of action-filled microvilli encompassing a stream producing apical flagellum to catch microbes as prey. Without a doubt, choanoflagellate-like cells likely framed the reason for the development of creature epithelial cells that today give a specific hindrance to interceding cooperations with microscopic organisms.
In many choanoflagellates, including Salpingoeca rosetta, a formative program can be started with the end goal that solitary cells form into multicellular rosettes. Significantly, rosette advancement doesn't happen through cell collection. Rather, as in the improvement of a creature from a zygote, rosettes create from a solitary establishing cell that experiences sequential rounds of arranged cell division, with the sister cells remaining steadily follower.
Hence, the answer is "It assume that the bacterial cell,or a chemicals were released by the bacteria,and bind with a receptors on the plasma membrane".