page_title: Streamlining theory
section_title: Nitrogen-fixing marine cyanobacteria (UCYN-A)
hierarchical_section_title: Streamlining theory / Model organisms / Nitrogen-fixing marine cyanobacteria (UCYN-A)
caption_attribution_description: English: Bloom of cyanobacteria in a freshwater pond. This accumulation in one corner of the pond was caused by wind drift. It looked as if someone had dumped a bucket color into the water. Deutsch: "Blüte" von Cyanobakterien (oft auch als Blaualgenblüte bezeichnet) in einem Baggerweiher. Durch Winddrift wurde die direkt unter der Wasseroberfläche treibende dünn-schlierige Masse in einer Ecke des Gewässers konzentriert. Es sah aus, als hätte jemand einen Eimer Farbe ins Wasser gekippt.
context_page_description: Genomic streamlining is a theory in evolutionary biology and microbial ecology that suggests that there is a reproductive benefit to prokaryotes having a smaller genome size with less non-coding DNA and fewer non-essential genes. There is a lot of variation in prokaryotic genome size, with the smallest free-living cell's genome being roughly ten times smaller than the largest prokaryote. Two of the bacterial taxa with the smallest genomes are Prochlorococcus and Pelagibacter ubique, both highly abundant marine bacteria commonly found in oligotrophic regions. Similar reduced genomes have been found in uncultured marine bacteria, suggesting that genomic streamlining is a common feature of bacterioplankton. This theory is typically used with reference to free-living organisms in oligotrophic environments.
context_section_description: Nitrogen-fixing marine cyanobacteria are known to support oxygen production in oceans by fixing inorganic nitrogen using the enzyme nitrogenase. A special subset of these bacteria, UCYN-A, was found to lack the  photosystem II complex usually used in photosynthesis and that it lacks a number of major metabolic pathways but is still capable of using the electron transport chain to generate energy from a light source. Furthermore, anabolic enzymes needed for creating amino acids such as valine, leucine and isoleucine are missing, as well as some which lead to phenylalanine, tyrosine and tryptophan biosynthesis.
  This organism seems to be an obligate photoheterotroph that uses carbon substrates for energy production and some biosynthetic materials for biosynthesis. It was discovered that UCYN-A developed a reduced genome of only 1.44 Megabases that is smaller but similar in structure to that of chloroplasts. In comparison with related species such as Crocosphaera watsonii and Cyanothece sp., which employ genomes  which range in length from 5.46 to 6.24 megabases, the UCYN-A genome is much smaller. The compacted genome is a single, circular chromosome with “1,214 identified protein-coding regions”. The genome of UCYN-A is also highly conserved ( >97% nucleotide identity) across ocean waters, which is atypical of ocean microbes. The lack of UCYN-A genome diversity, presence of nitrogenase and hydrogenase enzymes for the TCA cycle, reduced genome size and coding efficiency of the DNA suggest that this microorganism may have symbiotic lifestyle and live in close association with a host. However, the true lifestyle of this microbe remains unknown.
caption: Cyanobacteria blooms on a lake
exif: {"Image Make": "PENTAX", "Image Model": "PENTAX K-01", "Image Orientation": "Horizontal (normal)", "Image XResolution": "240", "Image YResolution": "240", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop Elements 9.0 Windows", "Image DateTime": "2014:07:11 19:32:00", "Image Artist": "Christian Fischer", "Image Copyright": "Christian Fischer", "Image ExifOffset": "276", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "870", "Thumbnail JPEGInterchangeFormatLength": "3838", "EXIF ExposureTime": "1/200", "EXIF FNumber": "9", "EXIF ExposureProgram": "Aperture Priority", "EXIF ISOSpeedRatings": "100", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2014:07:11 08:29:46", "EXIF DateTimeDigitized": "2014:07:11 08:29:46", "EXIF ShutterSpeedValue": "477741/62500", "EXIF ApertureValue": "126797/20000", "EXIF ExposureBiasValue": "-7/10", "EXIF MeteringMode": "CenterWeightedAverage", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "15", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2000", "EXIF ExifImageLength": "1333", "EXIF SensingMethod": "One-chip color area", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Manual Exposure", "EXIF WhiteBalance": "Auto", "EXIF FocalLengthIn35mmFilm": "22", "EXIF SceneCaptureType": "Standard", "EXIF Contrast": "Normal", "EXIF Saturation": "Soft", "EXIF Sharpness": "Hard", "EXIF SubjectDistanceRange": "2", "EXIF LensSpecification": "[15, 15, 4, 4]", "EXIF LensModel": "smc PENTAX-DA 15mm F4 ED AL Limited"}