Effect of low‑frequency ultrasound on disaggregation, growth and viability of an extremotolerant cyanobacterium

Abstract

The eficacy of low-frequency ultrasound pulses in cell disaggregation of Chroococcidiopsis sp. aggregates has been studied as a possible strategy to improve the productivity and operation of the cultures. The modulation of the ultrasound pulses allowed to almost disaggregate most of the cyanobacterial aggregates completely while retaining cellular viability in terms of photosynthetic efciency. In this study we used a strain isolated from the endolithic habitat of the Atacama Desert, the driest desert in the world due to the extremely scarce rainfall, low level of relative humidity and extremely high incident solar radiation. To survive these conditions and reduce the cell exposure to the incident UV radiation, Chroococcidiopsis sp. grows in the form of aggregates, diminishing the associated photo-oxidative damage. However, this adaptation strategy can reduce the availability of both light and nutrients to the growing cells. This study showed that the low-frequency ultrasound pulses were efcient in disaggregating Chroococcidiopsis sp. aggregates, improving light and nutrient availability to the cells. Our results revealed also that the modulated use of ultrasound pulses resulted in a decreased cell sedimentation velocity which becomes advantageous at large scale. The length of the ultrasound pulses can be optimized to achieve complete disaggregation of the aggregates without afecting cell viability. The preservation of cell viability is considered an dvantage for eventual large-scale production as disaggregating of the aggregates can result in more omogeneous cultures with less energy needed to perform mechanical agitation. Additionally, our results indicated an improved growth of cyanobacterium in disaggregated cultures.