SandTraps are efficient, scalable, and mild systems for harvesting, washing and concentrating cells

•We present a mild and efficient method for harvesting microbial cells on silica columns•The method allows non-contaminating harvest under oxic or anoxic conditions preserving microbial and enzymatic activity•The method is adaptable to different culture volume and bacterial cell sizes•Harvesting of extremely small microorganisms

Microbial cells vary widely in size, specific density, shearing resistance, oxygen sensitivity and abundance so that differential harvesting and washing procedures are needed to efficiently recover cells from dilute suspensions. We here describe a mild, simple, variable and cost-efficient method to harvest cells on columns packed with silica beads. The method collects and concentrates 40-98% of the cells preserving enzymatic activity and cell viability. The method can be applied for strictly anaerobic microorganisms, is scalable to different culture volumes and can be multiplexed in standardized systems. We see major application potential in harvesting small cells leaking through 0.2 μm filters, for harvesting strictly anaerobic cells and for differential harvesting of cells according to cell size using a gradient system.