The importance of harvesting time on the screening of Chlamydomonas spp. extracts for antibacterial activity

Photosynthetic green microalgae are investigated for their ability to produce metabolites with antibacterial activity. During microalgal screening for antibacterial activity, researchers usually choose a relatively random harvesting day in either exponential or early stationary phase. However, little is known about whether microalgae produce metabolites exhibiting antibacterial activity throughout their growth phase, or at what point they produce the maximum amount. For mass screening for activity, harvesting time is a key factor and accurate information if it can be conducted during the exponential phase or it has to wait until the onset of the stationary phase is of essential knowledge. In this study, extracts from five Chlamydomonas spp., collected from different water bodies (Ontario, Canada) and previously shown to have inhibitory activity against Staphylococcus aureus were investigated for antibacterial activity through their exponential growth phase until the onset of the stationary phase. The results demonstrated that as extracts exhibited antibacterial activity over the entire growth, they could be sampled for an initial screening early in the exponential phase, but if a high level of activity is required, it is suggested that harvesting the biomass should occur towards the end of the exponential phase.