SUMMARY: The properties of various mutants showed that, in the presence of an inorganic nitrogen source, agar utilization by requires the action of at least three groups of enzymes: a diffusible or cell-free extracellular agarase, some further degradative step(s), and the enzymes of galactose metabolism. Two unselected mutations (), both leading to loss of diffusible agarase and an undefined second agar utilization function, were detected among a small number of derivatives from a culture collection, and mapped to the 9 o'clock ‘silent’ region of the genetic map. One of these mutations () had apparently resulted, directly or indirectly, from the insertion of the plasmid SCP1 in this region during formation of the NF fertility type. The other () was 100% linked to and the integrated SCP1, but only 98% linked to the site of insertion of SCP1 in an ‘NF-like’ but Dag strain. SCP1-chromosome interactions in other regions of the genetic map had no effect on the agar-solubilizing phenotype, nor had three other unstable genetic phenomena in .


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