Synechococcus and Biofuel

Synechococcus is a genus of unicellular marine cyanobacteria that are found in both freshwater and marine water environments. They comprise a vast majority of picoplanktonic marine cyanobacteria. [1] Species in this genus are capable of photoheterotrophic, chemoheterotrophic, photoautotrophic, and even nitrogen fixation. [2] The genomes of several species of Synechococcus have been fully sequenced, most notably Synechococcus elongatus strain PCC 7942 and species strain WH8102. Due to the diversity in its metabolism as well as a genome that can be readily manipulated, Synechococcus holds potential for biofuel production via these metabolic pathways

Introduction

Classification

Taxonomy

Bacteria; Cyanobacteria; Chroococcales; Synechococcus [3]

Cell Structure

Synechococcus are coccoid shaped bacteria that range in size from 0.2-2 µm. They are classified as Gram-negative cells since the cell envelopes of these cyanobacteria structurally resemble those of Gram-negative bacteria, consisting of a cell membrane, peptidoglycan layer, outer membrane, surface layer, and sometimes additional structures. [4] [5]

Membrane structure of Synechococcus (strain WH8113) The inset corresponds to the outlined section of cell envelope comprising cell membrane (CM), peptidoglycan layer (P), outer membrane (OM), and surface layer (S). A thylakoid layer (T) is also indicated. This picture was published in 2001 by Aravinthan DT Samuel, Jennifer D. Petersen and Thomas S. Reese.[6

] Synechococci species are both motile and non-motile, although many motile species appear to accomplish their movement without the aid of a flagella. Cells are thought to undergo locomotion through a gilding fashion, using filamentous protrusions (pili or spicules) to make contact with cell surfaces and move in a direction parallel to the filament (directional motility). [7] Swimming motility is believed to be accomplished by surface waves generated by filamentous protrusions. It is proposed that the waves are generated by a motor force embedded in the cell membrane, although the exact mechanism is unclear. [6]

Envrionment & Lifecycle

Synechococcus are found in both the coastal marine environment as well as the pelagic zone (open sea). The environment in which these cyanobacteria are found in is important to regulation of their cell cycles, as factors such as light-dark cycle can affect Synechococcus cell cycles. Gaps in DNA synthesis are found between groups of cells that were exposed to light and exposed to dark. It has been determined that the Synechococcus cell cycle is light-dependent. [8] Synechococcus has 2 modes of cell cycle regulation. The first mode was consistent with the slow-growth model of the prokaryotic cell cycle. The second mode involved unsynchronized chromosome replication, with variability in chromosome copies amongst cells. The second mode serves as a poor estimator of colony growth rate due to the variation in distribution of DNA in the cells adding a probalistic component. [9] Synechococcus undergoes all phases of the cell cycle, although the duration of these phases is dependent upon growth rate and environment. Environmental conditions such as presence of nitrogen can affect the doubling time of the colonies as well as the duration of each phase of the cell cycle (S, G1, G2). Liu et al. found in 1999 that when grown under nitrogen-limited conditions, "(1) the fraction of cells in the S and G2 phases relatively constant, and (2) the cellular carbon, nitrogen and pigment content of this strain and their ratios vary with growth rate." [10] This study illustrated the relationship between physiological characteristics and the cell cycle of Synechococcus, providing greater insight as to better predicting the growth rate of these species.

Metabolism

Discuss various pathways of metabolism

Further Reading

[Sample link] Ebola Hemorrhagic Fever—Centers for Disease Control and Prevention, Special Pathogens Branch

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by (Caitlyn Young), a student of Nora Sullivan in BIOL168L (Microbiology) in The Keck Science Department of the Claremont Colleges Spring 2014.