Response of bacterioplankton to iron fertilization of the Southern Ocean, Antarctica.

Sanjay K Singh,Hara Kishore Kankipati,Sathyanarayana Reddy Gundlapally,Pasupuleti Sreenivasa Rao,Raj K Kapardar,Sundareswaran R Vetaikorumagan,Sisinthy Shivaji,Pratibha Mambatta Sankaranarayanan,Arunasri Kotakonda,Ramaiah Nagappa

doi:10.3389/fmicb.2015.00863

Abstract

Ocean iron fertilization is an approach to increase CO2 sequestration. The Indo-German iron fertilization experiment “LOHAFEX” was carried out in the Southern Ocean surrounding Antarctica in 2009 to monitor changes in bacterial community structure following iron fertilization-induced phytoplankton bloom of the seawater from different depths. 16S rRNA gene libraries were constructed using metagenomic DNA from seawater prior to and after iron fertilization and the clones were sequenced for identification of the major bacterial groups present and for phylogenetic analyses. A total of 4439 clones of 16S rRNA genes from ten 16S rRNA gene libraries were sequenced. More than 97.35% of the sequences represented four bacterial lineages i.e. Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes, and Firmicutes and confirmed their role in scavenging of phytoplankton blooms induced following iron fertilization. The present study demonstrates the response of Firmicutes due to Iron fertilization which was not observed in previous southern ocean Iron fertilization studies. In addition, this study identifies three unique phylogenetic clusters LOHAFEX Cluster 1 (affiliated to Bacteroidetes), 2, and 3 (affiliated to Firmicutes) which were not detected in any of the earlier studies on iron fertilization. The relative abundance of these clusters in response to iron fertilization was different. The increase in abundance of LOHAFEX Cluster 2 and Papillibacter sp. another dominant Firmicutes may imply a role in phytoplankton degradation. Disappearance of LOHAFEX Cluster 3 and other bacterial genera after iron fertilization may imply conditions not conducive for their survival. It is hypothesized that heterotrophic bacterial abundance in the Southern Ocean would depend on their ability to utilize algal exudates, decaying algal biomass and other nutrients thus resulting in a dynamic bacterial succession of distinct genera.

Highlights

Oceans are a major source and sink for carbon (Coale et al, 1996) with the marine phytoplankton fixing up to 40% of the carbon dioxide (CO2) (Hassler et al, 2011)
Chlorophyll a Concentration, Total Prokaryotic Cell Count, and Bacterial Production Chlorophyll a concentration at St-139 up to 40 m depth was >3 times (p < 0.001) compared to the concentrations at St114 indicating that iron fertilization has caused an increase in chlorophyll containing organism
At St-139, the chlorophyll a ranged between 0.13 and 1.58 mg m−3 while it was 0.10 and 0.75 mg m−3 in the non-fertilized water columns (Figure 2A). Both stations showed a decrease in mean total prokaryotic cell count (TPC) with depth (Figure 2B) and TPC in the fertilized waters was slightly higher compared to non-fertilized station

Summary

Introduction

Oceans are a major source and sink for carbon (Coale et al, 1996) with the marine phytoplankton fixing up to 40% of the carbon dioxide (CO2) (Hassler et al, 2011). Factors that hinder CO2 fixation by marine phytoplankton would impact global climate due to increase in the levels of CO2 in the atmosphere. Ocean iron fertilization and bacterial community microzooplankton) and abiotic factors (deficiency in the micronutrient iron) could decrease the levels of CO2 sequestered. The assumption is that if iron deficiency is overcome by exogenous addition of iron it would facilitate a phytoplankton bloom and lead to CO2 sequestration. The bloom could be grazed by microzooplankton and excreted as fecal pellets. These two processes would bring about CO2 fixation (Smetacek and Naqvi, 2008)

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