Evidence for a biogenic, microorganismal origin of rock varnish from the Gangdese Belt of Tibet

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  • Journal Identication = JMIC Article Identication = 1592 Date: March 10, 2011 Time: 5:1pm

    Micron 42 (2011) 401411

    Contents lists available at ScienceDirect


    journa l homepage: www.e lsev ier .com

    Evidence for a biogenic, microorganismal origin oGangdese Belt of Tibet

    Xiaohong SchKlaus Pe lerb

    a National Reseb Institute for P , D-55c Institute of Ged Max Planck In

    a r t i c l

    Article history:Received 4 NoReceived in reAccepted 2 De

    Keywords:VarnishTibetBiogenic mineralizationMicroorganismsBiolmMars

    aterie X-rdevelron mae ba

    layer in those samples two forms of bacteria-like microorganisms exist; cocci as tightly packed bacterialaggregates [within varnish bodies], and bacillus-like microorganisms [within the varnish matrix, thatsurrounds the varnish bodies]. The bacillus-like forms are embedded in a network of laments that havediameters between 35 and 45nm. These bacilli with the surrounding laments are assumed to havebeen involved in biolm formation (synthesis of extracellular polymeric substances) prior to their live

    1. Introdu

    Rock va(1807) for tadverse climpotential binish, a termof thin coatmicrometerSharp, 1958et al., 2003clay mineraganese [Mnand Post, 2and electronanalyses th

    Corresponberg UniversitTel.: +49 6131 Correspon

    E-mail add(W.E.G. Mller

    0968-4328/$ doi:10.1016/j.burial. We concluded that the formation of the varnish layers was for the most part biogenically drivenby microorganisms.

    2010 Elsevier Ltd. All rights reserved.


    rnish has interested geo-biologists since Humboldtwo reasons, rst to understand mineral formation inates and second to obtain further insights into the

    ogenic basis for mineral formation on Mars. Rock var-established by Dorn and Oberlander (1980), consists

    ings on rock surfaces, measuring usually between a fewand 3mm (reviewed in Laudermilk, 1931; Engel and; Broecker and Liu, 2001; Hodge et al., 2005; Perrya, 2004). Varnish is a brown-black layered veneer ofl on rocks that is rich in oxides and hydroxides of man-] and iron [Fe] (Potter and Rossman, 1977; McKeown001; Garvie et al., 2008). In spite of intensive light--microscopic investigations coupledwith geochemicale mechanism of nucleation and growth of rock var-

    ding author at: Institute for Physiological Chemistry, Johannes Guten-y, Medical School, Duesbergweg 6, D-55099 Mainz, Germany.39 25910; fax: +49 6131 39 25243.ding author. Tel.: +49 6131 39 25910; fax: +49 6131 39 25243.resses: wxh0408@hotmail.com (X. Wang), wmueller@uni-mainz.de).

    nish remains uncertain (Israel et al., 1997; Dorn, 1998; Perry et al.,2003a, 2004).

    The main components of rock varnish, Fe and Mn are widelyused in the organic world as cofactors for electron transfer pro-cesses (see Ehrlich, 2002; Tebo et al., 2005; Edwards et al., 2005).Two mechanisms of oxidation have been distinguished: rst theassimilatory metabolism of Mn and Fe, which involves cellularuptake and subsequent function in the cell metabolism, and sec-ond, the dissimilatory metabolism in which Mn and Fe serveeither as energy source or as terminal electron acceptor, depend-ing on the oxidation state (Ehrlich, 2002). While in the assimilatorymetabolism, small quantities of Mn and Fe are involved per cell,in the dissimilatory metabolism, much larger quantities of Mn andFe are involved and consumed per cell. Moreover, in the assimila-tory metabolism, Mn and Fe need to be taken into the cell whilein the dissimilatory metabolism (energy metabolism) Mn and Feappear to be acted upon on or in the cell envelope. During thosemetabolic processes the metal can be deposited in the terres-trial and aquatic environment on organic templates (see Glasby,2006; Wang and Mller, 2009), as has been determined for man-ganese/polymetallic nodules (Wang et al., 2009c) or crusts (Wanget al., 2009a, 2009b). These forms of organic template-driven min-eralization have been termed biomineralization by LowenstamandWeiner (Lowenstam and Weiner, 1989; see also Weiner and Dove,

    see front matter 2010 Elsevier Ltd. All rights reserved.micron.2010.12.001Wanga,b,, Lingsen Zengc, Matthias Wiensb, Uteter Jochumd, Heinz C. Schrderb, Werner E.G. Mlarch Center for Geoanalysis, 26 Baiwanzhuang Dajie, CHN-100037 Beijing, Chinahysiological Chemistry, Johannes Gutenberg University, Medical School, Duesbergweg 6ology, Chinese Academy of Geological Sciences, CHN-100037 Beijing, Chinastitute for Chemistry, J.J. Becherweg 27, D-55128 Mainz, Germany

    e i n f o

    vember 2010vised form 2 December 2010cember 2010

    a b s t r a c t

    In the present study we examined mperformed by use of energy dispersivwhether the varnish layers that hadvarnish bodies and silica glaze. Electis covered both by lamentous hyph/ locate /micron

    f rock varnish from the


    099 Mainz, Germany

    al from the Ashikule Basin of Tibet. Chemical analyses wereay spectroscopy and electron probe microanalysis to clarifyoped on the surface of the rhyolite are indeed composed oficroscopic analyses revealed that the surface of the varnishcterial and cocci-shaped forms. Within the varnish mineral

  • Journal Identication = JMIC Article Identication = 1592 Date: March 10, 2011 Time: 5:1pm

    402 X. Wang et al. / Micron 42 (2011) 401411

    2003). Biomineralization refers to those mineralization processesthat occur in close association with organic molecules or matri-ces or is even (micro)biologically mediated. While mineralizationfollows exclusively chemical and physical principles and results inthe accumuparticipatiotion are indinduced miorganic scaof biologicametallic no2009b) whare themajoton of largeet al., 2008;

    Rock dessemi-arid rDeserts of tPotter and(Krumbeinof WesterntheGangdethe formatibeen proposition of thet al., 1985)the ferromato capillarythermore, tand rain, asand Sharp,Rossman, 1(Perry et altion of micanalysis ofstrong evidhas been pthe presencmanganesevarnish asinitiation oflarge variet2006). In adhas been derole has alsoGeorge et aproposed th(Allen et al.et al., 2002)tion by extrin older var(Perry andsea manganBoussingaurial stromathas been de

    The growabout 40nated layersituations,mtal moisturIn turn roctal processemore, varnitures andvacycle of sul

    rock varnish has attracted archeologists to date petroglyphs thatwere etched into varnish by ancient cultures (Dragovich, 2000;Watchman, 2000).

    In the present study we investigated rock varnish from thele Basin of Tibet. This region has been characterized to showity tally tn ofessue Ml precrrestcentlrnislazen varthreerialNo dregithe vrstlybod

    s tha. Scaia aresubstown000)oilscmaes, list ong elion c


    ck v

    Linzngdey (70Centet al.he Ysystetheese Bndiay meby rostudyatedmedthe re Oliat 2

    re w-K rRIMPnisht to ef recithilation of inorganic materials from solution without anyn of organic molecules, the processes of biomineraliza-uced on the surfaces of organic templates [biologicallyneralization], or are almost entirely controlled by anffold [biologically controlled mineralization]. Exampleslly induced mineralization are the formations of poly-dules (Wang et al., 2009c) or crusts (Wang et al., 2009a,ereas biologically controlled mineralization processesrprinciple in the formationof thehard, inorganic skele--sized animals (see Weiner and Dove, 2003; SchrderMller et al., 2009).ert varnish coatings are formed in numerous arid and

    egions of the world, including the Sonoran and Mojavehe United States and Mexico (Engel and Sharp, 1958;Rossman, 1977), the Negev Desert in the Middle Eastand Jens, 1981), the Gibson and Great Victoria DesertsAustralia (Beard, 1970), and the Gobi Desert as well asse Belt region in Tibet of China (Krinsley et al., 2009). Foron of varnish abiogenic as well as biogenic origins havesed. The assumption of an inorganic, abiogenic depo-e varnish coatings (Potter and Rossman, 1977; Blumeis based on experiments suggesting that deposition ofnganese oxides within the clay matrix of varnish is duemovement of varnishing solutions from the rocks. Fur-he minerals have been proposed to originate from dustwell as from the surrounding soils (Allen, 1978; Engel

    1958; Scheffer et al., 1963; Krumbein, 1969; Potter and979). In a series of thorough studies the group of Perry., 2003b) provided strong evidence for the participa-roorganisms in growth of these rock coatings, e.g. bythe amino acid composition of varnish. Furthermore,ence for the existence of bacteria within the varnishrovided by Krumbein and Jens (1981) who observede of microorganisms with a potential for iron and/orprecipitation in these coatings on the surface of the

    well as within these minerals. Subsequently, biogenicvarnish formation was frequently suggested when of ay of bacteria was isolation (reviewed by Kuhlman et al.,dition, the isolation of fungi from the surfaces of varnishscribed (Staley et al., 1982; Staley et al., 1983) whosebeen implicated in varnish mineral formation (Taylor-

    l., 1983; Gorbushina et al., 1993). Finally, it had beenat varnish or varnish-like materials may exist on Mars, 2001; Guinness et al., 1997; Israel et al., 1997; Probst, and hence varnish might be a niche for the coloniza-aterrestrial life forms, such as bacteria. Often, especiallynishes a layered botryoidal structure has been observedAdams, 1978) which displayed similarities to the deepese nodules, a view that had already been discussed bylt (1882).Also similarityof thevarnishwithcyanobacte-olites (Monty, 1973; Krumbein and Lange-Giele, 1979)scribed.th rate of the varnish is slow and amounts to 1 to

    m per 1000 years (Liu and Broecker, 2000). The lami-ing of the varnish is surely an indicator for past climaticirroring especially the past alterations in environmen-

    e (Liu and Broecker, 2000; Broecker and Liu, 2001).k varnish harbors historical records for environmen-s, such as long-term climate changes (Liu, 2003). Evensh has been considered to preserve atmospheric signa-rnishdepositsmayprovide clues to thebiogeochemicalfur (Bao et al., 2001). It should also be mentioned that

    Ashikusimilarespeciabrasiolow-prbles thannuafor a tehas rerock vasilica gTibetalowingof bact2009).surfaceinsideexist; varnishganismmatrixbactermericare knet al., 2ing in sorganiphotypalso exscanniformat

    2. Ma

    2.1. Ro

    Thethe GaTertiarSouth-(Kappalong tthrustded inGangdof the Ioped beitherof thedominrial forNorth,and thlocatedrocks aof highthe SH

    Varrespecence othem wo the Mars environment (Krinsley et al., 2009). It ishe sediments, which consist of products from eolianlava that occurs at a cold, sulfate-rich, high elevation,re, and very dusty environment. Such a location resem-artian surface (Arocena et al., 2003), even though theipitation of 300mm (Dorn, 1998) is at the upper limitrial analogue of Mars. Varnish material from this regiony been described and was found to comprise distincth bodies, oval shaped accretions that are surrounded by(Krinsley et al., 2009). Interestingly, the surfaces of thenish comprise (living)Mn-enhancing bacteria of the fol-emorphotypes: (i) coccoid forms, (ii) lamentous formssize, and (iii) budding bacterial forms (Krinsley et al.,istinct microorganisms could be resolved in the sub-ons of those samples. In the present studywe show thatarnish two assemblages of fossilized microorganisms, cocci occurring in aggregates that are localized in theies and secondly, bacillus-like [rod shaped] microor-t exist outside the varnishbodies butwithin the varnish

    nning electron microscopic inspection revealed that theoften foundembedded in amatrix of extracellular poly-ances (EPS), displaying a lamentous morphology. EPSto be produced by biolm-forming bacteria (OToole, and are abundantly produced by microorganisms liv-(Or et al., 2007). This EPS contributes to 0.11.5% to thetter of soils (Chenu, 1995). Since the samebacterialmor-ike those found fossilized within the mineral material,n the surface of the varnish sample, as documented byectron microscopic imaging, we postulate that varnishan (at least partially) be ascribed to a biogenic origin.

    ls and methods

    arnish from the Ashikule Basin of Tibet

    izong Formation, that is located along the southern partse Belt, was formed during the Late Cretaceous to Early40Ma). The samples analyzed were collected in theral Gangdese Belt, that is located in the Sangsang area, 2007; Xie et al., in press); Fig. 1. This region is locatedarlung Tsangpo suture zone in the south. The Tanggulam is located in thenorth (Wanget al., 2008). It is embed-Gangdese retroarc thrust belt (Kapp et al., 2007). Theelt was shaped by magmatic events and tectonic driftsn and the Asia Plate. The Sangsang volcanic rocks devel-lting of the metasomatic lithospheric mantle, inducedlling-back or by breaking off from the Indian slab. Southarea in the Gangdese lies the fore-arc basin, a locationby the accumulation of the Shigatse ysch-like mate-during the Albian-Cenomanian age (Burg, 1983). To theesearch area is bordered by the Linzizong volcanic rocksgocene granite. The collection site (Ashikule Basin) is937N and 8641E at an altitude of 4900m. Volcanicidely distributed in that area and are composed mainlyhyolite mineral formed at 49.850.92Ma, as dated byzircon U/Pb age technique (Xie et al., in press).samples from the Ashikule Basin were studied withlement distribution and zonation as well as the pres-ent bacterial communities and the fossilized traces ofn the mineral layer.

  • Journal Identication = JMIC Article Identication = 1592 Date: March 10, 2011 Time: 5:1pm

    X. Wang et al. / Micron 42 (2011) 401411 403

    Fig. 1. Collect ed [realong the Sout s locatare marked by re zonlegend, the rea

    2.2. The clim

    Sangsanfrigid-sub-tclimate is reature shift aperiod laststime is >30annual raintions (Kapp

    2.3. Chemic

    The varAliquots ofof Li2B4O7analyzed byprocedure d

    2.4. Elemen

    The varnSM2500/SP(Leica Micrdiamond paslices energwith an EDAmicroscopeoperating arecorded an1994).

    Then, elepolished thC, Fe,Mn, P,Max Planck

    ev etm). Eccel

    ng timicr

    ticalion site of varnish samples in the Ashikule Basin, close to Sangsang (Tibet); markhern part the Gangdese Belt. South of the study area the Gangdese fore-arc basin idashed lines; TTS, Tanggula thrust system [North] and YZS, Yarlung Tsangpo sutuder is referred to the web version of the article.)

    ate condition in Sangsang area

    g is located within a plateau, characterized by a sub-emperate and semi-arid monsoon climate zone. Thelatively dry and cold with a marked day/night temper-nd a peak temperature of 10 C to 15 C. The frost-freeabout 105 days per year; the annual average sunshine

    00h. The wet and dry seasons are distinct. The average

    (Sobol(10n20kV acountiEPMA

    2.5. Opfall is about 250300mm allowing only sparse vegeta-et al., 2007).

    al analysis

    nish samples were ground to -200 mesh powder.0.5 g of the sample were thoroughly mixed with 5gand fused into a glass bead. Finally the material wasthe X-ray uorescence (XRF) technique following theescribed by Wu et al. (2008).

    tal analysis: EDX and EPMA

    ish sampleswere sliced (50300mthick)with a Leica2600 sliding microtome with ultramilling attachmentosystems, Nuloch, Germany) and polished with 1pmste (Engis Corp., Mort...


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