Drops join to make a stream: high-throughput nanoscale cultivation to grasp the lettuce root microbiome

Root endospheres house complex and diverse bacterial communities, of which many strains have not been cultivated yet by means of the currently available isolation techniques. The Prospector® (General Automation Lab Technologies, San Carlos, CA, USA), an automated and high-throughput bacterial cultivation system, was applied to analyse the root endomicrobiome of lettuce (Lactuca sativa L.). By using deep sequencing, we compared the results obtained with the Prospector and the traditional solid medium culturing and extinction methods. We found that the species richness did not differ and that the amount of previously uncultured bacteria did not increase, but that the bacterial diversity isolated by the three methods varied. In addition, the tryptic soy broth and King's B media provided a lower, but different, diversity of bacteria than that of Reasoner's 2A (R2A) medium when used within the Prospector system and the number of unique bacterial strains did not weigh up against those isolated with the R2A medium. Thus, to cultivate as broad a variety of bacteria as possible, divergent isolation techniques should be used in parallel. Thanks to its speed and limited manual requirements, the Prospector is a valuable system to enlarge root microbiome culture collections.