We use spatially sculptured light for user-interactive micromanipulation of mixed yeast cell populations to analyze growth behavioural patterns. There is negligible absorption in the near-infrared region of the light spectrum making it suitable for direct manipulation of individual cells in a growing population. Rather than using a single-beam optical trap, multiple cells are manipulated using a system based on the Generalized Phase Contrast (GPC) method, which allows arbitrary trapping configurations i.e. control over the number of traps, and the size/shape of each trap. This enables the cells to be selectively trapped in all three-dimensions (3D) and manipulated in real-time while under direct observation. Here, we impose controlled experiments using these multiple 3D optical traps to show the alteration of growth patterns in mixed cultures of Saccharomyces cerevisiae and Hanseniaspora uvarum experiencing spatially constrained conditions.