Impact of DNA damaging agents on genome-wide transcriptional profiles in two marine Synechococcus species

Sasha G Tetu,Chris L Dupont,Daniel A Johnson,Deepa Varkey,Rhona K Stuart,Brian Palenik,Karl A Hassan,Ian T Paulsen,Katherine Phillippy

doi:10.3389/fmicb.2013.00232

Sasha G Tetu, Chris L Dupont + Show 7 more

Open Access

https://doi.org/10.3389/fmicb.2013.00232

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Abstract

Marine microorganisms, particularly those residing in coastal areas, may come in contact with any number of chemicals of environmental or xenobiotic origin. The sensitivity and response of marine cyanobacteria to such chemicals is, at present, poorly understood. We have looked at the transcriptional response of well characterized Synechococcus open ocean (WH8102) and coastal (CC9311) isolates to two DNA damaging agents, mitomycin C and ethidium bromide, using whole-genome expression microarrays. The coastal strain showed differential regulation of a larger proportion of its genome following “shock” treatment with each agent. Many of the orthologous genes in these strains, including those encoding sensor kinases, showed different transcriptional responses, with the CC9311 genes more likely to show significant changes in both treatments. While the overall response of each strain was considerably different, there were distinct transcriptional responses common to both strains observed for each DNA damaging agent, linked to the mode of action of each chemical. In both CC9311 and WH8102 there was evidence of SOS response induction under mitomycin C treatment, with genes recA, lexA and umuC significantly upregulated in this experiment but not under ethidium bromide treatment. Conversely, ethidium bromide treatment tended to result in upregulation of the DNA-directed RNA polymerase genes, not observed following mitomycin C treatment. Interestingly, a large number of genes residing on putative genomic island regions of each genome also showed significant upregulation under one or both chemical treatments.

Highlights

IntroductionUnicellular marine cyanobacteria, including Synechococcus and Prochlorococcus species, are estimated to constitute 20–40% of total marine chlorophyll biomass and carbon fixation, and significantly impact the carbon cycle and global climate processes (Partensky et al, 1999)
Ocean environments comprise a vast component of the Earth’s biosphere and play a key role in global biogeochemical processes.Unicellular marine cyanobacteria, including Synechococcus and Prochlorococcus species, are estimated to constitute 20–40% of total marine chlorophyll biomass and carbon fixation, and significantly impact the carbon cycle and global climate processes (Partensky et al, 1999)
Chemical treatments were performed using each compound at a concentration that was inhibitory to long-term growth, 2 μg/mL for ethidium bromide (EB)

Summary

Introduction

Unicellular marine cyanobacteria, including Synechococcus and Prochlorococcus species, are estimated to constitute 20–40% of total marine chlorophyll biomass and carbon fixation, and significantly impact the carbon cycle and global climate processes (Partensky et al, 1999) Considering their ecological importance, it is important to understand what stresses these organisms are susceptible to and how they respond to these challenges. Phosphate limitation stress is an issue in some marine environments and a subset of cyanobacteria encode the PhoB/R two component regulatory systems for responding to this (Tetu et al, 2009) Another www.frontiersin.org challenge is high irradiance, especially UV wavelengths (Llabres and Agusti, 2006), and adaptation to high light conditions in marine Synechococcus involves expression of genes whose products are involved with dissipation of excess light, scavenging to eliminate reactive oxygen species and changes to photosynthetic machinery (Scanlan et al, 2009; Mella-Flores et al, 2012)

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