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Applied and Environmental Microbiology, February 2000, p. 455-466, Vol. 66, No. 2
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Limitation of Bacterial Growth by Dissolved Organic Matter and Iron in the Southern Oceandagger

Matthew J. Church,1,* David A. Hutchins,2 and Hugh W. Ducklow1

School of Marine Science, The College of William and Mary, Gloucester Point, Virginia 23062-1346,1 and College of Marine Studies, University of Delaware, Lewes, Delaware 199582

Received 17 August 1999/Accepted 10 November 1999

The importance of resource limitation in controlling bacterial growth in the high-nutrient, low-chlorophyll (HNLC) region of the Southern Ocean was experimentally determined during February and March 1998. Organic- and inorganic-nutrient enrichment experiments were performed between 42°S and 55°S along 141°E. Bacterial abundance, mean cell volume, and [3H]thymidine and [3H]leucine incorporation were measured during 4- to 5-day incubations. Bacterial biomass, production, and rates of growth all responded to organic enrichments in three of the four experiments. These results indicate that bacterial growth was constrained primarily by the availability of dissolved organic matter. Bacterial growth in the subtropical front, subantarctic zone, and subantarctic front responded most favorably to additions of dissolved free amino acids or glucose plus ammonium. Bacterial growth in these regions may be limited by input of both organic matter and reduced nitrogen. Unlike similar experimental results in other HNLC regions (subarctic and equatorial Pacific), growth stimulation of bacteria in the Southern Ocean resulted in significant biomass accumulation, apparently by stimulating bacterial growth in excess of removal processes. Bacterial growth was relatively unchanged by additions of iron alone; however, additions of glucose plus iron resulted in substantial increases in rates of bacterial growth and biomass accumulation. These results imply that bacterial growth efficiency and nitrogen utilization may be partly constrained by iron availability in the HNLC Southern Ocean.

* Corresponding author. Mailing address: The College of William and Mary, School of Marine Science, P.O. Box 1346, Gloucester Point, VA 23062-1346. Phone: (804) 684-7401. Fax: (804) 684-7399. E-mail: mattc{at}vims.edu.

dagger U.S. J.G.O.F.S. contribution number 545. V.I.M.S. contribution number 2277.

Applied and Environmental Microbiology, February 2000, p. 455-466, Vol. 66, No. 2
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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