Areas of actjive volcanic activity are cliaract,erized b y specific environmental conditions, among t.hem a.re : high temperatures, sometimes very low pH values of water and rocks, sharp fluctuations of the oxidat,ion-reduction potential, etc. However, some ~nicrobiologists ( E M O T O 1929, 1933; KUZNETSOV 1955 and others) testify t,hat a various and abundant microflora can be found even under these specific ecological conditions.
Almost all microbiological studies in act,ive volcanic areas deal with the microflora of thermal springs. The distribution and thc role of microorganisms in the circulation of substances in c r a t a lakcs are much less known. We can mention only SIJZTJKI'S work (Suzurrr and NIMURA 1960, SUXUKI 1961) who has discovered Th. thiooaitlans in the acid lake Kat>anuma and a paper by LJUNGGREN wlio finds in t h e waters of the crater lake Ixpaco (Guatemala), with pH = 2.3, a rapid reproduct.ion of Beggicctoa (LJUNGGREN 1960).
The rolc of bact'eria in the cyclc of sulpliur in c,rnt,er lakes is especially interesting since it^ is known t>hat t,lie wat,er of t)liese lakes often cont,ains a great amount of sulphur compounds of different valency (H,S, SO,, SO,, Sql) while the bot,t,om deposits of crat,er lakes accumulate much native sulphur which in many ~o u n t ~r i e s is used as industrial material (VLASOV 1960, LJUNGGREN 1960, TAKEO 1962). Taking into account) t)Iiat all principal phases of the sulphur cycle in usual rescrvoirs are connectcd with t,hr act>ivity of various microorganisms (Ihe transformation of sulphur compounds under specific conditions observed in crat.er lakes. Hence, the aim of our study carried out during t,he suninier of 1962 in crater lakes of tho Golovnin caldera (Iiunashir island, the Kurils) was t o st,udy the clistribution of sulpli"te-retlucing, tliionic (7'h. thiopnius, Th. thioozidans, Th. ferroc.ridms) and sulphur hacteria in t>he waters and silt) deposits of lakes Kipyaslichyee (Roiling) ant1 Goryachyee (Hot), t o invest'igate some hydrochemical propcrt,ies of watcr and siks affccting the act>ivit,y of bact,eria and t o st'udy thc IJ~OIXSS of sulphur :iccum ulntion in silt deposits of thc lakes nicnt'ioned abovc.
I . L)eaci,ipl iotL of /,he Kipytcshchyee n i d the Goryachyee lakes
Both Idws differ rathcr considerably in size, maximum depths, hydrochemical. a n t 1 temperaturc regimes. The smaller one, the liipyashchyee, lies