The isolated microalgae propagated mainly via asexual reproduction forming sporangia containing two to eight autospores (Figure 2d). After shedding the sporangium wall, the newly formed cells remained attached to each other for a long time; as a result, the culture tended to accumulate four-cell clusters. Under non-optimal cultivation conditions, e.g., in a highly diluted culture, small, pear-shaped fast-moving biflagellate cells similar to gametes as described by Triki et al. [15] were encountered. Occasionally, these cells underwent conjugation resembling isogamous sexual process (Figure 2e). Dead cells with transparent content were also present in the culture (not shown). One could conclude that the life cycle and cell morphology recorded in the BM1 isolate as well as the ability to accumulate the red pigment in the ―red‖ cells are consistent with the characteristic traits of Haematococcus pluvialis Flotow [15–17].
To characterize the newly isolated microalga, we investigated its cell ultrastructure. It should be noted that ultrastructural studies of H. pluvialis are generally more difficult in comparison to most of green microalgae, mainly due to the presence of tough cell walls complicating the chemical fixation, embedding and preparation of ultrathin sections [18]. Indeed, we found that the thick cell wall of BM1 was, like that of H. pluvialis aplanospores, extremely resistant to mechanical disruption andchemical agents and presented difficulties for electron microscopy. Nevertheless, both transmission (Figure 3a,c,d) and scanning (Figure 3b) electron micrographs of ―green‖ and ―red‖ BM1 cells were obtained.