Cyanobacteria gene and protein sequences in diurnal oscillation metabolic processes
2010
Daytime photosynthesis and nighttime nitrogen fixation metabolic processes have been reported in the
bacterium, Cyanothece 51142. The organism's auto-fluorescence with 532 nm excitation would place
cyanobacteria at the forefront in the remote sensing of microbial activity in astrobiology. The sensitivity of
nitrogenase to oxygen was studied in terms of sequence nucleotide fluctuation. A nucleotide sequence fractal
dimension can be calculated from a numerical series consisting of the atomic numbers of each nucleotide. The
fractal dimension and Shannon entropy form a two-dimensional measure that is useful in assessing evolutionary
pressures. The studied sequences include nitrogenase iron protein NifH, nitrogenase molybdenum-iron protein
alpha chain NifD and beta chain NifK. The photosynthesis-lacking UCYN-A cyanobacterium as reported
recently in the journal, Nature, was observed to have the lowest entropy with relatively high fractal dimension
values in the studied NifH, NifD and NifH sequences. The fractal dimension of NifH sequences correlates with
the NifD sequence values with an R-square of 0.91 (N = 8). The Shannon mononucleotide entropy of NifD
sequences correlates with the NifK sequence values with an R-square value of 0.92 (N = 8). The observed strong
correlation suggests the presence of gradual evolutionary pressure among the studied cyanobacteria, and throws
light on the reported paradox in evolution for the case of UCYN-A. The results show that diurnal oscillation
metabolic processes in cyanobacteria (including the photosynthesis-deficient case) are not associated with
extraordinary evolutionary pressures and thus are processes consistent with putative astrobiological organisms.
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