Pelagibacter ubique

Pelagibacter ubique is probably the most common type of bacteria. It was originally called SAR11 and was known only by their ribosomal RNA, which was first identified in 1990 in samples from the Sargasso Sea. The bacteria responsible for this were isolated and named in 2002.

P. ubique occurs all over the world and lives as part of the plankton, thus free floating in the oceans. They are among the smallest reproductive cells with a diameter of only 0.12 to 0.20 microns.

With only 1354 genes, these bacteria have a relatively small genome. It contains less paralogs than any other studied free-living cell, no viral genes and very little non-coding DNA. P. ubique are therefore a very efficient form of life, whatever their mass exemplary occurrences confirmed.

General ubique to Pelagibacter

The P. ubique strain consists of very small marine α - Protebakterien, they are found in all oceans and account for some 25% of all cells. It is the first cultured member of the α - Protebakterien. It has been the smallest genome of all known reproductive cells, and has for all 20 amino acids biosynthetic functions. P. ubique is growing by the water dissolved carbon compounds and gets its energy from a light-controlled pump proteorhodopsin and cellular respiration. In studies of the genome of P. ubique, it was found to contain DNA -receptive genes and suspected due to the fact that P. ubique is able to take up foreign DNA. In these studies, it is also found that the proportion of guanine and cytosine in the genome located at approximately 29.7%. Since most of the transporters in the P. ubique have a very high substrate affinity, less energy is consumed in the form of ATP, which also explains the viability of large populations in nutrient- poor media.

Ubique cultivation of Pelagibacter

In the cultivation of P. ubique natural microbial communities were diluted and isolated in very low-dose nutrient media. The culture medium consisted of sterile water from coastal Oregon, the phosphate ( KH2PO4 ), ammonium ( NH 4 Cl ) and a mixture of defined carbon compounds was added. In the isolation of the cells, the fact you made ​​himself the advantage that the substrate concentrations in natural seawater are approximately three times smaller than in laboratory media. After isolation they marked the array of P. ubique cultures by FISH ( fluorescence in situ hybridization ) to improve the visibility microscope.

After incubation at 15 ° C for 23 days in the dark or in a 14h/10h light-dark cycle, small volumes of the cultures were applied to a polycarbonate membrane. We then analyzed the intergenic nucleotide sequences of the isolated cultures, and found that there are three genetically distinct groups, each of which differ by only a few nucleotides, or an insertion or deletion. Since two of the three groups ( the third contains only one culture), the incubation both in the light-dark cycle, and took place only in the dark, you could exclude the influence of light.

The maximum cell density varied between 2.5 * 10 cells per ml, and 3.5 × 10 cells per ml, depending on where and when the samples were removed, but is independent of the carbon compound. Based on these results, it is assumed that natural factors control the population of P. ubique. This is of great importance for oceanographic research, because this leads to the conclusion that you could identify with the study of the growth of P. ubique chemical factors in the water. Through a BLAST search of paralogous gene families, it was found that P. ubique must have originated from a duplication event out.