Bacterioplankton of low and high DNA content in the suboxic waters of the Arabian Sea and the Gulf of Oman : abundance and amino acid uptake

Amino acid uptakes by bacterioplankton of low DNA (LNA) and high DNA (HNA) con- tent, populating the oxygen minimum zone (OMZ: 0.998, p < 0.0001) with leucine incorporation into protein and with microbial glucose uptake, suggesting that bacterioplankton growth was controlled by dissolved organic matter, and that methionine uptake could be used as a general estimate for the metabolic activity of bacterioplankton. The varia- tion in methionine uptake depended on the prokaryote group rather than on ambient oxygen concen- tration, e.g. the numerically dominant LNA cells took 3 to 5 times less precursor than the HNA cells. A percentage of the LNA cells with double the amount of DNA was proposed as an incubation-inde- pendent index of growth of the cells in the G2 stage of the cell cycle. The vertical profiles of the per- centage of LNA cells in G2 showed pronounced peaks at 300 to 600 m in the OMZ that did not corre- late with peaks of either total bacterioplankton abundance or productivity. The present paper underlines the importance of bacterioplankton group studies in the OMZ since high microbial cell abundance does not necessarily mean high metabolic activity and other mechanisms, such as resilience to mortality pressure, have to be investigated.

[1]  C. Turley.  The effect of pressure on leucine and thymidine incorporation by free-living bacteria and by bacteria attached to sinking oceanic particles , 1993 .

[2]  Rudolf Amann,et al.  Molecular identification of picoplankton populations in contrasting waters of the Arabian Sea , 2005 .

[3]  D. Kirchman,et al.  Estimating Bacterial Production in Marine Waters from the Simultaneous Incorporation of Thymidine and Leucine , 1988, Applied and environmental microbiology.

[4]  Howard M. Shapiro,et al.  Practical Flow Cytometry , 1985 .

[5]  J. Fuhrman,et al.  Significance of Size and Nucleic Acid Content Heterogeneity as Measured by Flow Cytometry in Natural Planktonic Bacteria , 1999, Applied and Environmental Microbiology.

[6]  R Amann,et al.  Flow sorting of microorganisms for molecular analysis , 1997, Applied and environmental microbiology.

[7]  Philippe Lebaron,et al.  Does the High Nucleic Acid Content of Individual Bacterial Cells Allow Us To Discriminate between Active Cells and Inactive Cells in Aquatic Systems? , 2001, Applied and Environmental Microbiology.

[8]  F. Azam,et al.  Bacterial community composition during two consecutive NE Monsoon periods in the Arabian Sea studied by denaturing gradient gel electrophoresis (DGGE) of rRNA genes , 1999 .

[9]  H. Ducklow.  Bacterioplankton distributions and production in the northwestern Indian Ocean and Gulf of Oman, September 1986 , 1993 .

[10]  J. S. Godfrey,et al.  Regional Oceanography: An Introduction , 1994 .

[11]  D. Vaulot,et al.  Enumeration and Cell Cycle Analysis of Natural Populations of Marine Picoplankton by Flow Cytometry Using the Nucleic Acid Stain SYBR Green I , 1997, Applied and environmental microbiology.

[12]  S. Naqvi.  Denitrification processes in the Arabian Sea , 1994, Journal of Earth System Science.

[13]  B. Biddanda,et al.  Bacterial utilization of dissolved glucose in the upper water column of the Gulf of Mexico , 1999 .

[14]  C. Francis,et al.  Diversity of nitrite reductase genes (nirS) in the denitrifying water column of the coastal Arabian Sea , 2004 .

[15]  Stefan Schouten,et al.  Distribution of Membrane Lipids of Planktonic Crenarchaeota in the Arabian Sea , 2002, Applied and Environmental Microbiology.

[16]  R. Amann,et al.  Comparison of Cellular and Biomass Specific Activities of Dominant Bacterioplankton Groups in Stratified Waters of the Celtic Sea , 2001, Applied and Environmental Microbiology.