MORPHOGENESIS OF LABORATORY BIOFILMS

Microbial structures make up the majority of the first 3 b.y. of the fossil record. Reproducing structures similar to those made by ancient microbes in the lab provides valuable insight into the behavior of early microbial communities.  This study uses a model system of Pseudanabaena sp., from Martinez, CA to analyze the morphological development of cyanobacterial biofilms under different conditions.  These filaments organize into complex networks of peaks and ridges. The geometry of initial networks is influenced by the surface on which the biofilms grow, whereas later growth and morphological development are impacted by dissolved inorganic carbon (DIC) and pH. Biofilm morphology does not vary except at low DIC and extremely high pH.  In media with low DIC and circum neutral pH, biofilms produce pillars with "fuzzy" tops. These biofilms are starved for carbon, which causes vertical movement of cells towards higher CO₂ concentrations, followed by the extension of cells beyond the pillars to form "fuzzy" tops that maximize CO₂ delivery per cell.  In contrast, biofilms grown at pH 11 behave differently. They produce initial networks that are small and discontinuous, and the biomass increases very slowly.  Biofilms grown at pH 10 and lower with sufficient DIC all produce more robust networks that grow through time.  Thus, there is a distinct morphological change between pH 10 and 11, which correlates to the conversion of HCO^- to CO₃^2- in the media.  The lack of growth suggests that biofilms grown at pH 11 are CO₂ starved and unable to use CO₃^2- for photosynthesis.  Their behavior may be different than biofilms grown at low DIC and circum neutral pH because any CO₂ dissolving into the media at the surface of the cultures converts to CO₃^2-.  Thus, there is no CO₂ gradient within the media to induce pillar formation.  Results to date are from a single cyanobacterial species. We will proceed with characterization of biofilm morphogenesis using a second cyanobacterial model system from Lake Pavilion, BC, which has been established in the previous year.  This system produces intricate networks in the field, and comparisons among laboratory biofilms, natural structures, and ancient microbialites  may lead to identification of structures that uniquely reflect certain microbial behaviors, such as network formation.