Bailliez et al. (1986) found that the immobilized B. braunii cultures in calcium alginate beads had higher chlorophyll and photosynthetic activities compared to their free cells. S. obliquus cells immobilized in alginate (Brouers et al. 1983), and C. vulgaris and Anacystis nidulans in agar (Kayano et al. 1981; Weetall and Krampitz 1980), also showed a significant increase in their chlorophyll content. Enhanced chlorophyll and photosynthetic activity was explained by the protection of immobilized cells from photoinhibition due to the self-shadowing effect, and a possible increase in the concentrations of particular ions in the microenvironment of cells which can improve photosynthesis (Bailliez et al. 1986; Tamponnet et al. 1985).

Individually co-immobilized cells of C. vulgaris and C. sorokiniana with A. brasilense growth-promoting bacterium also yielded higher chlorophyll a and b, violaxanthin, and lutein accumulation compared to the immobilized algal cells without any bacterium (de-Bashan et al. 2002a).

Lebeau et al. (2000) reported that the immobilization of the marine diatom Haslea ostrearia in agar had a positive effect on the continuous production of the marennin pigment, which is primarily used for the oyster-breeding industry.

Some potential limitations of the secondary product formation by immobilized cells are the commonly reported slower growth rates of the microorganisms compared to their free-cell suspension systems and slower diffusion rates of the target-products (i. e., hydrogen) from the cells into their environment. Resolving these issues with the combination of optimized immobilization matrices and innovative bioreactor designs (e. g., some attempts include membrane-based cell recycle bioreactor (Chang et al. 1994); dual-layer coaxial hollow fiber-type biore­actor (Yang et al. 2006); and a multimembrane bioreactor in a pressure cycling mode (Efthymiou and Shuler 1987), aiming to increase the nutrient transfer to the cells) can potentially bring other dimensions to the research areas of those afore­mentioned bioprocesses.