Diversity of Growth Patterns Probed in Live Cyanobacterial Cells Using a Fluorescent Analog of a Peptidoglycan Precursor.

Ju-Yuan Zhang,Wei-Yue Xing,Cheng-Cai Zhang,Gui-Ming Lin

doi:10.3389/fmicb.2018.00791

Ju-Yuan Zhang, Wei-Yue Xing + Show 2 more

Open Access

https://doi.org/10.3389/fmicb.2018.00791

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Abstract

Cyanobacteria were the first oxygenic photosynthetic organisms during evolution and were ancestors of plastids. Cyanobacterial cells exhibit an extraordinary diversity in their size and shape, and bacterial cell morphology largely depends on the synthesis and the dynamics of the peptidoglycan (PG) layer. Here, we used a fluorescence analog of the PG synthesis precursor D-Ala, 7-Hydroxycoumarin-amino-D-alanine (HADA), to probe the PG synthesis pattern in live cells of cyanobacteria with different morphology. They displayed diverse synthesis patterns, with some strains showing an intensive HADA incorporation at the septal region, whereas others gave an HADA signal distributed around the cells. Growth zones covering several cells at the tips of the filament were present in some filamentous strains such as in Arthrospira. In Anabaena PCC 7120, which is capable of differentiating heterocysts for N2 fixation, PG synthesis followed the cell division cycle. In addition, an HADA incorporation was strongly activated from 12 to 15 h following the initiation of heterocyst development, indicating a thickening of the PG layer in heterocysts. The PG synthesis pattern is diverse in cyanobacteria and responds to developmental regulation. The use of fluorescent analogs may serve as a useful tool for understanding the mechanisms of cell growth and morphogenesis operating in these organisms.

Highlights

Cyanobacteria are the only prokaryotes capable of oxygenic photosynthesis
Cyanobacterial cells show a high diversity in their shape, with sizes ranging from approximately 0.5 μm in the case of marine
Our results showed an increased PG synthesis activity during heterocyst maturation, after the deposition of the polysaccharide layer, which led to a thick layer of PG surrounding the mature heterocyst

Summary

INTRODUCTION

Cyanobacteria are the only prokaryotes capable of oxygenic photosynthesis. Their occurrence on the Earth dates back to at least 2.45–2.32 Ga, but they may have first appeared even earlier, as evidenced by the fossils records (Bekker et al, 2004; Jeltsch, 2013). The PG layer is a macromolecule that surrounds bacterial cells and maintains cell shape It is composed of a polymer network of N-acetylglucosamine and N-acetylmuramic acid cross-linked with pentapeptide chains. FtsZ treadmilling directs the dynamic synthesis of PG during cell constriction, whereas MreB coordinates the activity of the elongasome (Bisson-Filho et al, 2017; Yang et al, 2017) Both MreB and FtsZ are cytoskeletal elements (Busiek and Margolin, 2015) and are conserved in cyanobacteria (Zhang et al, 1995; Sakr et al, 2006; Hu et al, 2007). Several fluorescent D-amino acids (FDAAs) have been developed to probe the growth mode in bacterial cells by revealing the active part in a cell where PG synthesis occurs (Kuru et al, 2015). These results increase our understanding of the molecular mechanisms underlying PG synthesis and cellular morphogenesis in cyanobacteria

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DISCUSSION