Abstract

The effect of ultraviolet irradiation on diatom-derived dissolved organic matter used as a bacterial growth substrate was investigated. The dissolved organic matter fraction of 100–1000 daltons (low molecular weight) was prepared from a culture of a marine diatom, Chaetoceros sp. This dissolved matter was then exposed to ultraviolet-A and -B irradiation at naturally occurring intensities of 0–44 kJ m-2. The concentration of low-molecular-weight dissolved organic matter decreased as ultraviolet irradiation increased, which was a reflection of photolytic mineralization of the material.

The irradiated organic matter was added to the culture of a Vibrio strain to assess its bioavailability. Bacterial growth was enhanced with the irradiated material, which was probably due to the photolytic production of more bioavailable monomeric substrates. The loss of the low-molecular-weight dissolved organic material concentration was counterbalanced by enhanced bioavailability. Thus, ultraviolet irradiation of the natural diatom-derived low-molecular-weight dissolved organic matter pool may be net-positive for the growth of marine bacteria.

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References

Amon, R.M.W. and Benner, R.
1996
.
Bacterial utilization of different size classes of dissolved organic matter
.
Limnol. Oceanogr.
,
41
:
41
51
.
Benner, R., Pakulski, J.D., McCarthy, M., Hedges, J.I. and Hatcher, P.G.
1992
.
Bulk chemical characteristics of dissolved organic matter in the ocean
.
Science
,
255
:
1561
1564
.
Chrost, R.H. and Faust, M.A.
1983
.
Organic carbon release by phytoplankton: its composition and utilization by bacterioplankton
.
J. Plankton Res.
,
5
:
477
493
.
Graneli, W., Lindell, M. and Tranvik, L.
1996
.
Photo-oxidative production of dissolved inorganic carbon in lakes of different humic content
.
Limnol. Oceanogr.
,
41
:
698
706
.
Guillard, R.R.L. and Ryther, J.H.
1962
.
Studies of marine planktonic diatoms I. Cyclotella nana Hustedt and Detonula confervacea (Cleve) Gran
.
Can. J. Microbiol.
,
8
:
229
239
.
Kieber, D.J., McDaniel, J. and Mopper, K.
1989
.
Photochemical source of biological substrates in sea water: implications for carbon cycling
.
Nature
,
341
:
637
639
.
Lindell, M., Graneli, W. and Tranvik, L.
1995
.
Enhanced bacterial growth in response to photochemical transformation of dissolved organic matter
.
Limnol. Oceanogr.
,
40
:
195
199
.
Lovley, D.R., Coates, J.D., Blunt-Harris, E.L., Phillips, E.J.P. and Woodward, J.C.
1996
.
Humic substances as electron acceptors for microbial respiration
.
Nature
,
382
:
445
448
.
Miller, W.L. and Zepp, R.G.
1995
.
Photochemical production of dissolved inorganic carbon from terrestrial organic matter: significance to the oceanic organic carbon cycle
.
Geophys. Res. Lett.
,
22
:
417
420
.
Menzel, D.W. and Ryther, J.H.
1970
. “
Distribution and cycling of organic matter in the oceans
”. In
Organic Matter in Natural Waters, Institute of Marine Science, University of Alaska, Alaska
,
Occasional Publication No. 1
Edited by: Hood, D.W.
31
54
.
In
Mopper, K., Zhou, X., Kieber, R.J., Kieber, D.J., Silkorski, R.J. and Jones, R.D.
1991
.
Photochemical degradation of dissolved organic carbon and its impact on the oceanic carbon cycle
.
Nature
,
353
:
60
62
.
Morris, D.P., Zagarese, H., Williamson, C.E., Balseiro, E.G., Hagreaves, B.R., Modenutti, B., Moeller, R. and Queimalinos, C.
1995
.
The attenuation of solar UV radiation in lakes and the role of dissolved organic carbon
.
Limnol. Oceanogr.
,
40
:
1381
1391
.
Murakami, Y.
1999
.
Effects of a bacterial siderophore on microalgal proliferation
,
School of Biosphere Science, Hiroshima University
.
MSc thesis
Naganuma, T. and Miura, S.
1997
.
Abundance, production and viability of bacterioplankton in the Seto Inland Sea
.
Japan. J. Oceanogr.
,
53
:
435
442
.
Naganuma, T., Konishi, S., Inoue, T., Nakane, S. and Sukizaki, S.
1996
.
Photodegradation or photoalteration? Microbial assay of the effect of UV-B on dissolved organic matter
.
Mar. Ecol. Prog. Ser.
,
135
:
309
310
.
Naganuma, T., Inoue, T. and Uye, S.
1997
.
Photoreactivation of UV-induced damage to embryos of a planktonic copepod
.
J. Plankton Res
,
19
:
783
787
.
Obernosterer, I. and Herndl, G.J.
1995
.
Phytoplankton extracellular release and bacterial growth: dependence on the inorganic N:P ratio
.
Mar. Ecol. Prog. Ser.
,
116
:
247
257
.
Sundh, I.
1992
.
Biochemical composition of dissolved organic carbon derived from phytoplankton and used by heterotrophic bacteria
.
Appl. Environ. Microbiol.
,
58
:
2938
2947
.
Thomas, D.N. and Lara, R.J.
1995
.
Photodegradation of algal dissolved organic carbon
.
Mar. Ecol. Prog. Ser.
,
116
:
309
310
.
Wetzel, R.G., Hatcher, P.G. and Bianchi, T.S.
1995
.
Natural photolysis by ultraviolet irradiance of recalcitrant dissolved organic matter to simple substrates for rapid bacterial metabolism
.
Limnol. Oceanogr.
,
40
:
1369
1380
.