MOTILITY AND MORPHOGENESIS IN A CYANOBACTERIAL BIOFILM

Microbialites dominate the first three billion years of Earth's fossil record and have the potential to provide valuable insights into the behavior of ancient microbial communities. However, details about microbial processes and functions would greatly increase our knowledge of the evolution of Earth's early biosphere, but are difficult to extract from the rock record. Fortunately, modern cyanobacteria build complex biofilms with diverse morphological features, providing us with a laboratory in which we can improve our understanding of fundamental biological behaviors that contribute to the development of complex morphology.

To elucidate processes contributing to morphogenesis in cyanobacterial biofilms, we developed a model system consisting of a single cyanobacterium, Pseudanabaena sp. Cyanobacterial slurries rapidly organize into complex structures over several hours via cell motility. Biofilm growth also can contribute to the development of complex structures, although not on the same short timescale. Cell motility and biofilm organization are light dependent, but light is not the fundamental determinant of morphology. Rather, morphology is highly dependent on substrate, e.g. structures are different on smooth, impermeable plastic; glass beads; natural sand; and clays. Unique narrow peak structures develop under conditions of restricted gas exchange, suggesting that CO2 limitation promotes the development of steeper structures.

Observations of this laboratory system have established that motility plays a vital role in generating complex biofilm morphologies that are distinct from abiotic structures and are similar to specific modern and ancient microbialites. We are continuing to study the morphological dynamics of this biofilm system, specifically: 1) how the individual motion of bacteria produce macroscopic structures, and 2) how environmental factors influence morphology.