Culture strains of Emiliania huxleyi (Lohmann 1902) Hay et al. 1967 were placed into two groups designated E. huxleyi type A and type B on the basis of coccolith morphology and immunological properties of the coccolith polysaccharide. We studied the distribution of these types in the North Atlantic region using an indirect immunofluorescence assay with antisera directed against the coccolith polysaccharide of E. huxleyi type A and type B and epifluorescence microscopy. In field samples taken in the Northeast Atlantic Ocean, E. huxleyi type A was found exclusively. In contrast, type B was dominant in the North Sea. Scanning electron microscopy of the samples revealed the same unequal distribution of the two types as found with the immunofluorescent‐labelling assay.
SummaryThe manganese-oxidizing factor of Pseudomonas putida strain GB-1 is associated with the outer membrane. One of the systems of protein transport across the outer membrane is the general secretory pathway (Gsp). The gsp genes are called xcp in Pseudomonas species. In a previous study, it was shown that mutation of the prepilin peptidase XcpA and of a homologue of the pseudopilin XcpT inhibited transport of the factor. In the present study, we describe the genomic region flanking the xcpT homologue (designated xcmT1 ). We show that xcmT1 is part of a twogene operon that includes an xcpS homologue (designated xcmS ). No other xcp -like genes are present in the regions flanking the xcmT1 / xcmS cluster. We also characterized the site of transposon insertion of another transport mutant of P. putida GB-1. This insertion appeared to be located in a gene (designated xcmX ) possibly encoding another pseudopilin-related protein. This xcmX is clustered with two other xcpT -related genes (designated xcmT2 and xcmT3 ) on one side and homologues of three csg genes (designated csmE , csmF and csmG ) on the other side. The csg genes are involved in production of aggregative fibres in Escherichia coli and Salmonella typhimurium . A search for XcmX homologues revealed that the recently published genome of Ralstonia solanacearum and the unannotated genome of P. putida KT2440 contain comparable gene clusters with xcmX and xcp homologues that are different from the well-described 'regular' xcp / gsp clusters. They do contain xcpR and xcpQ homologues but, for example, homologues of xcpP , Y and Z are lacking. The results suggest a novel Xcp-related system for the transport of manganese-oxidizing enzymes to the cell surface.
Emiliania huxleyi (Lohmann) Kamptner, belonging to a group of marine unicellular algae, the Coccolithophoridae, possesses a cell wall containing calcified structures called coccoliths. These coccoliths contain a water‐soluble acid polysaccharide. The polysaccharide contains ester sulphate and uronic acid groups and binds Ca2+ preferentially from a medium also containing Na+ and Mg2+. It is thought to perform a regulatory function in the calcification process. In the present paper we describe a series of studies in vivo intended to give a preliminary characterization of a number of metabolic steps leading to coccolith formation. In view of the putative role of the acid polysaccharide in coccolith synthesis, we have concentrated on the incorporation of polysaccharide precursors by calcifying cells. As a second approach we investigated the differences between calcifying cells and cells of the same species that have lost the capability to produce coccoliths (non‐calcifying cells). Calcifying cells were offered radioactive calcium, bicarbonate, galactose and sulphate in the light. Most of the calcium label and a small part of the label of galactose and bicarbonate was incorporated into extracellular coccoliths. The label of galactose was detected in at least seven of the constituent monosaccharides of the coccolith‐associated polysaccharide. Radioactive sulphate was also incorporated into the extracellular coccolith polysaccharide. In contrast to the label of bicarbonate and galactose that of calcium reached a steady‐state concentration intracellularly within 2 h. A technique was developed for the isolation of intracellular CaCO3, presumably coccoliths in statu nascendi. About 10% of the label of bicarbonate and galactose was incorporated into an intracellular acid polysaccharide, resembling the coccolith‐associated macromolecule. Non‐calcifying cells fail to take up Ca2+ and galactose. We demonstrated that non‐calcifying cells produce an acid polysaccharide, resembling the coccolith‐associated macromolecule. The former polysaccharide is shed into the surrounding medium and can be labelled by offering the non‐calcifying cells radioactive bicarbonate.
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