Opal-A and Associated Microbes from Wairakei, New Zealand

Mineralogical Magazine, June 2003, Vol. 67(3), pp.563–579 Opal-Aandassociated microbes from Wairakei,NewZealand:the first 300 days 1, 2 3 B. Y. SMITH *, S. J. TURNER AND K. A. RODGERS 1 Department of Geology, University of Auckland, Private Bag 92019, Auckland, NewZealand 2 School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, NewZealand 3 Research Associate, Australian Museum, Sydney, NSW2000, Australia ABSTRACT Allsamples of silica sinter, <2 y oldtaken from the discharge drain of the Wairakei geothermal power stationand the Rainbow Terrace of Orakei Korako, consist of non-crystalline opal-A. This silica phase depositsdirectly upon the concrete drain wall and filamentous templets, extending from this wall, affordedby the microbial community present in the drain, whose nature was determined by a culture- independentstrategy that entailed construction, fingerprinting and sequencing of a 16Sclone library. Thebacterial community is dominated by five major groups of organisms, present in approximately equalproportions, and which account for ~50% of the community. None of the 16S sequences from thesedominant groups yielded a perfectmatch with 16S sequences for named organisms in the internationaldatabases. However one dominant group clusters with Hydrogenophilusthermoluteus , a thermophilicfilamentous bacterium, and two cluster with putatively thermophilic members of the Cyanobacteria andgreen non-sulphur bacteria respectively. Initial opal-A deposits rapidly as agglomerationsof silica nanospheres that, in turn, form chains of coalesced, oblate, microspheres <0.460.2 mmaboutthe barbicel-like filaments, to produce a matof fine woven strands. The majority ofindividual filaments are <8 mmlongand 0.8 mmwidebut may be up to 55 mm long by 1 mm wide. Wherelaminar flow dominates, most strands develop parallel to the drain current but some strands crisscrosswhile others protrude above the mat surface. Where flow is turbulent, strands lack preferred orientationand some adopt a helicalform. In general, following deposition, the values of the scattering broadbandat half (FWHM) andthree quarters (FWTM) ofthe maximum intensity decrease with increasingsample age. The behaviour of the band at one quarter maximum intensity (FWQM) isless consistent,but, in general, the youngest sinters possess the highest FWQM, FWHM andFWTM values thatprove independent of fabric type. Opal-A silica matures following its removal from the parent fluid,especially where the sinter surface is filmed by water. A continualmovement of silica is shown bya secondgeneration of microspheres formed on the silica mat surface, by an increase in size of the initialmicrospheres, and by an increase in maximum intensity of the X-ray scattering broadbands. Similarsilica aging behaviour occurs among young sinters developed upon microbial mats at Orakei Korako.The deposition and aging processes accord with the known behaviour of juvenile opaline silica inboth natural and artificial systems whose pH, temperature and dissolved salt content are similar to Wairakeiand Rainbow terrace: gelling of silica is favoured by the high pH (~8.3) and temperature (~60ºC) oftheWairakei discharge fluid but the high dissolved salt content of the water (Na + = 930 mg/g, Ca2+ = 12 mg/g,Cl =1500 mg/g)and abundant microbial community facilitate rapid and copious flocculationof solid silica within the drain, in contrast to the slower accumulation on the natural sinter terraceat lower temperature (30 –45ºC) fromless saline dilute bicarbonate-chlori dewaters (Na + = 180 mg/g, Ca2+ = 0.2 mg/g, Cl = 400 mg/g,pH = 8.1). KEY WORDS: sinter,Wairakei, New Zealand,bacterial community, microbes. *E-mail: [email protected] DOI: 10.1180/0026461036730118 # 2003The Mineralogical Society B.Y. SMITHETAL. Introduction Theresults presented here constitute a rststep towardsobtaining a totalpicture of thesingular and WHEN rstdeposited, sinter from near-neutral intimatecharacter of the primary microbe-mineral alkalichloride waters consists of opal-A, a non- connectionin the rstdays of silicadeposition. crystalline,hydrated silica phase (Smith, 1998; Followingdepositionupon the microbi al Herdianita et al., 2000a).Whileall materials that substrate,Herdianita et al. (2000a)demonstrated comein contactwith discharging thermal waters, thatchanges occur in both the physical properties bethey biogenic or abiogenic, can afford a andin the textures of theopal-A silica phase, such potentialsubstrate for the coagulating silica, it thatthe primary depositional textures, including haslong been known that microbes such as the anybacterial templets, are modi ed to varying Cyanobacteriaand Archaea thatthrive in the hot degrees.Ultimately, opal-A transforms with time springenvironments, are particularly effective at intoparacrystalline opal-CT and/ oropal-C, and, mediatingthe deposition of theopaline silica (e.g. subsequently,to microcrystall inequartz. The Weed, 1889a,b).Thesilica occulatesupon and maturationprocess typically takes ~50,000 y for aboutthe different microbial templets to produce TaupoVolcanic Zone (TVZ) sinters. mouldsof the lamentswith a rangeof distinctive Inorder to appraisefossil textures it isessential texturesthat have become the focus of particular tounderstand the manner and extent of any interestin recent years (e.g. Cady and Farmer, modications an opal-A mould may undergo. 1996;Farmer, 2000). WhileHerdianita’ s et al. (2000a)modelof sinter Thenature of the microbial communitie s agingis helpful in this respect, all samples of involvedin the silica sinter depositional process opal-Awith an ageof 41ywereplotted by these andthe mechanisms of microbe-mediated silici- authorson a single,year-1 time line, i.e. no cationare, as yet, unclear. Much of our lack of indicationwas given as to whether changes understandinghas stemmed from our inability to occurredin the physical character of opal-A culture,and hence identify and study in vitro, the duringits rstyear. In pointof fact,they recorded vastmajority of environm entallyassociat ed arangeof valuesin theproperties of their year-1 microbes.The recent development of culture- samplesthat is greater than any seen among independentmolecular methods provides a solu- samplesa fewyears old. tionto this problem by enabling the nature of Giventhat a supplyof oldersinter, available at microbialcommunities to be determined from Wairakei,was deposited in distinct time brackets bacterialDNA extracteddirectly from environ- overprevious months, the opportunity was also mentalsamples (Amann et al., 1995). 16S takento investigate whether the spread of values ribosomalRNA (rRNA)genes are a useful observedby Herdianita et al. (2000a) re ects targetfor these analyses as they are highly mineralogicalprocesses initiated immediately conserved,being found in all microorganisms, uponor soon after deposition, following the whilealso containing variable sequence regions, entombmentand silici cation of the bacterial orsignature sequences, that enable taxonomic precursors,i.e. what changes, if any, occur in classication organisms to the level of species. opalinesilica immediately following deposition. ComparativeDNA sequenceanalysis of 16S Sampleswith numbers pre xed AU areheld in genesis nowwidely used for the characterization theDepartm entof Geolog y,Univers ityof ofcomplex microbial communities and for the AucklandPetrology Collection. taxonomicdescription of microorganisms from a broaddiversity of environments including subsur- facescale at theOtake geothermal power station, Sampleoccurrence Japan(Inagaki et al.,1997)and Yellowstone hot Samplesare categorized into 3 groups(Table 1). springcommunities(Blank et al., 1999; Hugenholtz et al.,1998;Inagaki et al., 2001). Group A At theWairakei geothermal power station, New Zealand(Fig. 1), the discharge drain contains both Thickdeposits, typical of streamer microfacies anextens ivemicrob ialcommuni tyand an silica,accumulate at arateof a fewhundred mm/ y unlimitedsupply of fresh opal-A. Consequently, inthe drains used to discharge waste water from theopportunity exists to analyse both the nature theWairakei geothermal power station. These anddiversity of a microbialcommunity, and the drainsconsist of twoadjoining concrete channels initialsilica depositing amongst that community. each1.5 m wide.The build up of silica is such 564 OPAL-A AND ASSOCIATED MICROBES TVZ TVZ L. Taupo 0 200 km W a i k a t o R . Orakei Korako Wairakei Latitude 38.5S L. Taupo lake geothermal systems delineated by geophysical methods inferred caldera 0 10 20 30 km Longitude 175.5E FIG.1. Sketch map, showing the locations of Wairakei and Orakei Korako geothermal elds within the Taupo Volcanic Zone. Insert: North Island, NewZealand. thatthe drains become clogged and require feathers.An elongate strand or group of strands cleaningevery six months or so. A central formsa centralshaft or rachisthat can commonly dividerseparates the channels and was originally growup to50 mminlength. From this, numerous intendedto permiteach to be used independently barb-likestrands, commonly 5 –10 mm long, butground subside ncehas caused the hot divaricate.In turn, these subdivide to produce dischargewater level to overtop this divider and evensmaller barbicel-like laments,up to55 mm ithasbecome a primarysite for sinter deposition long,that interlock in a mannerakin to the (Fig.2). Flow rate is currently ~500 l/ swithwater barbicelhooks of feathers. Unlike feathers, coolingfrom 95º C atinputto ~60º C immediately however,the diameters of silica-coated rachi, abovea

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