Rapid Reactivation of Cyanobacterial Photosynthesis and Migration upon Rehydration of Desiccated Marine Microbial Mats.

Arjun Chennu,Dirk De Beer,Lubos Polerecky,Mohammad A A Al-Najjar,Alistair Grinham

doi:10.3389/fmicb.2015.01472

Abstract

Desiccated cyanobacterial mats are the dominant biological feature in the Earth’s arid zones. While the response of desiccated cyanobacteria to rehydration is well-documented for terrestrial systems, information about the response in marine systems is lacking. We used high temporal resolution hyperspectral imaging, liquid chromatography, pulse-amplitude fluorometry, oxygen microsensors, and confocal laser microscopy to study this response in a desiccated microbial mat from Exmouth Gulf, Australia. During the initial 15 min after rehydration chlorophyll a concentrations increased 2–5 fold and cyanobacterial photosynthesis was re-established. Although the mechanism behind this rapid increase of chlorophyll a remains unknown, we hypothesize that it involves resynthesis from a precursor stored in desiccated cyanobacteria. The subsequent phase (15 min–48 h) involved migration of the reactivated cyanobacteria toward the mat surface, which led, together with a gradual increase in chlorophyll a, to a further increase in photosynthesis. We conclude that the response involving an increase in chlorophyll a and recovery of photosynthetic activity within minutes after rehydration is common for cyanobacteria from desiccated mats of both terrestrial and marine origin. However, the response of upward migration and its triggering factor appear to be mat-specific and likely linked to other factors.

Highlights

Microbial mats are dense benthic communities of diverse species of bacteria, archaea, and eukaryotic microalgae organized in a sediment matrix (Paerl et al, 2000; Franks and Stolz, 2009)
We studied the response of a desiccated cyanobacterial mat from Giralia Bay in Exmouth Gulf, Australia over the temporal scale of minutes-todays after rehydration
The average spectrum showed the gradual development of the spectral signatures of cyanobacterial photopigments chlorophyll a and phycocyanin, with maximum in vivo absorption wavelengths at 678 and 630 nm, respectively (Figure 1C)

Summary

Introduction

Microbial mats are dense benthic communities of diverse species of bacteria, archaea, and eukaryotic microalgae organized in a sediment matrix (Paerl et al, 2000; Franks and Stolz, 2009). In arid and mesic zones of the tropical, temperate and polar regions, photosynthetic microbial mats are the dominant biological feature (Whitton and Potts, 2012). In these systems, cyanobacteria are the dominant primary producers and display high rates of carbon and nitrogen fixation despite being active only during sporadic events of water availability (Lovelock et al, 2010). Rapid Reactivation of Desiccated Cyanobacteria characteristized by steep vertical gradients of oxygen, pH, and sulfide These gradients change dramatically with diel periodicity due to variable input of light and these changes are generally thought to control the structure and distribution of the microbial communities in mats. The diel variations of light, oxygen, and sulfide are generally considered to be the key drivers for the motility of cyanobacteria in mats, other factors such as salinity gradient (Kohls et al, 2010) and desiccation state (Pringault and Garcia-Pichel, 2004) have been shown to play a role

Methods

Results

Conclusion