Laboratory horror stories: Poison in the agars

The fission yeast Schizosaccharomyces pombe is a single-celled eukaryote that can be cultured as a haploid or as a diploid. Scientists employ mating, meiosis, and the plating of ascospores and cells to generate strains with novel genotypes and to discover biological processes. Our two laboratories encountered independently sudden-onset, major impediments to such research. Spore suspensions and vegetative cells no longer plated effectively on minimal media. By systematically analyzing multiple different media components from multiple different suppliers, we identified the source of the problem. Specific lots of agar, from different suppliers, were toxic. Interestingly, the inhibitory effect was attenuated on rich media. Consequently, quality control checks that use only rich media can provide false assurances on the quality of the agar. Lastly, we describe likely sources of the toxicity and we provide specific guidance for quality control measures that should be applied by all vendors as preconditions for their sale of agar. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/597796v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@41d7c1org.highwire.dtl.DTLVardef@bbec24org.highwire.dtl.DTLVardef@18c6f76org.highwire.dtl.DTLVardef@e9b707_HPS_FORMAT_FIGEXP M_FIG C_FIG Take-awayO_LISporadically, batches of agar from different suppliers strongly inhibit the plating efficiency of S. pombe spores and vegetative cells on minimal media. C_LIO_LIQuality control checks that are not quantitative or that use only rich media can provide false assurances on the quality of the agar. C_LIO_LIVendors should conduct rigorous, thorough, organism-specific tests for potential toxicity of each lot of agar as a pre-condition for its sale. C_LI