The biosynthetic gene cluster for the 26-membered ring of the polyene macrolide pimaricin extends for about 110 kilobase pairs of contiguous DNA in the genome of Streptomyces natalensis. Two sets of polyketide synthase (PKS) genes are separated by a group of small polyketide-functionalizing genes. Two of the polyketide synthase genes, pimS0 and pimS1, have been fully sequenced and disrupted proving the involvement of each of these genes in pimaricin biosynthesis. The pimS0 gene encodes a relatively small acetate-activating PKS (ϳ193 kDa) that appears to work as a loading protein which "presents" the starter unit to the second PKS subunit. The pimS1 gene encodes a giant multienzyme (ϳ710 kDa) harboring 15 activities responsible for the first four cycles of chain elongation in pimaricin biosynthesis, resulting in formation of the polyene chromophore.

Particle sinking velocity is considered to be a controlling factor for carbon transport to the deep sea and thus carbon sequestration in the oceans. The velocities of the material exported to depth are considered to be high in high‐latitude productive systems and low in oligotrophic distributions. We use a recently developed method based on the measurement of the radioactive pair 210Po‐210Pb to calculate particle sinking velocities in the temperate and oligotrophic North Atlantic during different bloom stages. Our estimates of average sinking velocities (ASVs) show that slowly sinking particles (<100 m d−1) contribute significantly to carbon flux at all the locations except in the temperate regions during the bloom. ASVs appear to vary strongly with season, which we propose is caused by changes in the epipelagic community structure. Our results are the first field data to confirm the long‐standing theory that particle sinking velocities increase with depth, with increases of up to 90% between 50 and 150 m depth.

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