Biomass losses of Sodalinema alkaliphilum in alkaline, high pH, open raceway ponds

Abstract

Growing cyanobacteria in high pH (10+), high carbonate alkalinity medium (0.5 M) increases the driving force for CO₂ capture and helps exclude competitors and predators. But in these conditions, cyanobacteria might expend more energy to maintain osmotic gradients across their membrane. Thus, these extremophiles may respire more fixed carbon, increasing biomass losses compared to growth in milder conditions. In this work, a microbial consortium primarily composed of Sodalinema alkaliphilum (formerly Phormidium alkaliphilum) from alkaline soda lakes was grown in an outdoor open raceway pond. Night-time biomass losses were ca. 5 % by mass. Stable isotope probing (SIP) found respiration accounted for 0–2 % of daily biomass losses with no detectable difference in respiration rates between day and night. Comparisons of SIP and mass density measurements indicated respiration was not always the primary driver of biomass loss and that DOC release may contribute, even during stable operation. Proteomics and 16S rRNA DNA sequencing showed the abundance of bacterial heterotrophs was low with Cyclonatronum spp. representing the largest fraction (<1 %). The relative abundance of proteins within the S. alkaliphilum proteome was stable but the rate of protein synthesis varied. Overall rates of protein synthesis were highest in the afternoon (when photosynthesis was most active), but quality control proteins were preferentially made in the morning, likely in preparation for the work ahead. Understanding when and how biomass is lost in cultivation systems is crucial in informing efforts to improve biomass models and enhance biomass yield.