Náttúrufræðingurinn

						Sigurður Pétursson. 1958. Hveragróður. -

Náttúrufræðingurinn 28: 141- 151.

Sigurður   Pórarinsson.   1978.   Hverir   og

laugar,   ölkeldur  og   kaldavermsl.   —

Náttúruverndarráð,     Fjölrit    nr.     3,

Reykjavík: 14 bls.

Stefán Arnórsson & Einar Gunnlaugsson.

1985.  New gas geothermometers for

geothermal exploration - Calibration

and   application.    -   Geochimica   et

Cosmochimica Acta 49: 1307-1325.

Stetter, K.O. 1982. Ultrathin mycelia-

forming organisms from submarine

volcanic areas having an optimum

growth temperature of 105°C. - Nat-

ure 300: 258-260.

Stetter, K.O. & H. König. 1983. Leben

am Siedepunkt. - Spectrum der Wiss-

enschaft. Oktober: 26-40.

Stetter, K.O., M. Thomm, J. Winter, G.

Wildgruber, H. Huber, W. Zillig, D.

Janekovic, H. König, P. Palm & S.

Wunderl. 1981. Methanothermus fervi-

dus, sp. nov., a novel extremely therm-

ophilic methanogen isolated from an

Icelandic hot spring. - Zbl. Bakt.

Hyg., I. Abt. Orig. C 2: 166- 178.

Tryggvi Þórðarson. 1981. Varmalindir.

Hvítársíða, Hálsasveit og innanverður

Reykholtsdalur. Náttúruverndarkönn-

un. - Náttúruverndarráð, Fjölrit nr.

10, Reykjavík: 77 bls.

Tuxen, S.L. 1944. The hot springs of Ice-

land, their animal communities and

their zoogeographical significance. -

Zool. Icel. 1 (11): 1-206.

Zillig, W., K.O. Stetter, W. Schafer, D.

Janekovic, S. Wunderl, I. Holz & P.

Palm. 1981. Thermoproteales: A novel

type of extremely thermoacidophilic

anaerobic archaebacteria isolated from

Icelandic solfataras. - Zbl. Bakt.

Hyg., I. Abt. Orig. C 2: 205-227.

Zuber, H. 1979. Thermophile Bakterien.

Chemie in unserer Zeit 13(6): 165—

175.

Woese, C.R., L.J. Magrum & G.E. Fox.

1978. Archaebacteria. - J. Molec.

Evol. 11: 245-252.

Þorleifur Einarsson. 1978. Jarðfræði. 3.

útg. - Mál og menning, Reykjavík: 240

bls.

SUMMARY

Life in Icelandic hot springs

by

Jakob K. Kristjánsson

and Guðni Á. Alfreðsson

Institute of Biology

University of lceland

Grensásvegur 12, 108 Reykjavík

Temperature is probably the most im-

portant environmental factor affecting the

activities and evolution of living organ-

isms. Most organisms are adapted to „mo-

derate" temperatures but only microorg-

anisms are found at very high temperatur-

es, as in hot springs. Microorganisms with

optimum growth temperature (Topt) of

45-55°C are ubiquitous but those having

Topt 60°C or above are generally only fo-

und in thermal areas. The hot springs in

Iceland are chemically and physically very

diverse which explains the diversity of the

microorganisms living in the hot springs.

The most conspicuous organisms in the

low sulfide, alkaline hot springs are blue-

green algae (cyanobacteria) of the genera

Mastigocladus and Phormidium. They of-

ten form thick algal-bacterial mats up to

60°C (Fig. 2). Many different kinds of

thermophilic bacteria are known to grow

in these mats. In sulfide-rich alkaline hot

springs the growth of blue-green algae is

inhibited but photosynthetic bacteria of the

genus Chloroflexus flourish. They can form

long orange streamers up to about 70°C

(Fig. 3). If the sulfide concentration is very

high (>60 /xM) the growth of Chloroflexus

is also inhibited and sulfide- oxidizing bact-

eria of the genera Thermothrix and Thiobac-

illus take over. These bacteria can form thick

white mats, consisting of bacteria and prec-

ipitated sulfur granules (Fig. 5). Sulfide-

oxidizing bacteria are usually found in the

hot springs at 60-70°C but we have also

seen them at 90-95°C.

The acidic springs are also teeming with

life even though it is not as obvious as in

the alkaline springs. Most of the bacteria

67