Molecular microbial diversity of a soil sample and
Transcription
Molecular microbial diversity of a soil sample and
ARTICLE IN PRESS Microbiological Research 162 (2007) 15—25 www.elsevier.de/micres Molecular microbial diversity of a soil sample and detection of ammonia oxidizers from Cape Evans, Mcmurdo Dry Valley, Antarctica Bhupendra V. Shravage, Kannayakanahalli M. Dayananda, Milind S. Patole, Yogesh S. Shouche Molecular Biology Unit, National Centre for Cell Science, Ganeshkhind, Pune 411007, India Accepted 3 January 2006 KEYWORDS Antarctica; SSU rDNA clone library; Soil diversity Summary The aim of our study was to estimate the uncultured eubacterial diversity of a soil sample collected below a dead seal, Cape Evans, McMurdo, Antarctica by an SSU rDNA gene library approach. Our study by sequencing of clones from SSU rDNA gene library approach revealed high diversity in the soil sample from Antarctica. More than 50% of clones showed homology to Cytophaga—Flavobacterium–Bacteroides group; sequences also belonged to a, b, g proteobacteria, Thermus–Deinococcus and high GC gram-positive group; Phylogenetic analysis of the SSU rDNA clones showed the presence of species belonging to Cytophaga spp., Vitellibacter vladivostokensis, Aequorivita lipolytica, Aequorivita crocea, Flavobacterium spp., Flexibacter sp., Subsaxibacter broadyi, Bacteroidetes, Roseobacter sp., Sphingomonas baekryungensis, Nitrosospira sp., Nitrosomonas cryotolerans, Psychrobacter spp., Chromohalobacter sp., Psychrobacter okhotskensis, Psychrobacter fozii, Psychrobacter urativorans, Rubrobacter radiotolerans, Marinobacter sp., Rubrobacteridae, Desulfotomaculum aeronauticum and Deinococcus sp. The presence of ammonia oxidizing bacteria in Antarctica soil was confirmed by the presence of the amoA gene. Phylogenetic analysis revealed grouping of clones with their respective groups. & 2006 Elsevier GmbH. All rights reserved. Introduction Corresponding author. E-mail address: [email protected] (Y.S. Shouche). The McMurdo Dry Valleys of Antarctica has a unique climate. They are mostly ice-free throughout the year, with average annual temperatures around 22 1C and relative humidity of 14–47%. The 0944-5013/$ - see front matter & 2006 Elsevier GmbH. All rights reserved. doi:10.1016/j.micres.2006.01.005 ARTICLE IN PRESS 16 strong katabatic winds from the polar ice plateau create truly desert conditions (Friedmann et al., 1987). The soils of dry valleys were assumed to be abiotic (Horowitz et al., 1972). However, Friedmann and Ocampo (1976) first described the presence of microorganisms within the pore space of sandstones. Since then a considerable number of different microorganisms have been isolated from these habitats (Baublis et al., 1991; Dawid et al., 1988; Friedmann, 1980; Friedmann, 1982; Hirsch and Gallikowski, 1985; Hirsch and Gallikowski, 1998; Hirsch et al., 1988; Kappen and Friedmann, 1983). However, these studies do not give a complete picture about microbial community structure due to inherent drawbacks of cultural methods; such limitations are due to the reliance on selective media and to the fact many bacterial populations are refractory to cultivation (Head et al., 1998). Consequently, they provide an incomplete assessment of the community structure. In recent years, culture independent approaches, especially 16S rDNA-based methods have been used extensively for community analysis (Amann et al., 1995; Hugenholtz et al., 1998; Paster et al., 2001). In case of Antarctica most of the studies have concentrated on the microbial diversity of sea ice, lake sediments and cyanobacterial mat samples from lakes (Brambilla et al., 2001; Gordon et al., 2000; Taton et al., 2003). The rRNA approach has been used earlier to evaluate the bacterial diversity of habitats such as sub-glacial lake ice and perennial lake ice (Gordon et al., 2000), lake sediments (Bowman et al., 2000a, b; Sjoling and Cowan, 2003) and sediment core (Bowman et al., 2000a, b; Torsvik et al., 1996) and sea ice (Bowman et al., 1997) from Antarctica. There is only one report of such study for the soil samples from Schirmacher Oasis, Antarctica (Shivaji et al., 2003). The soil samples differ from the lake sediments or mats because they provide different ecological niches for microorganisms (Shivaji et al., 2003). In this paper, we report a study on a soil sample from McMurdo Dry Valley in Antarctica using SSU ribosomal gene clone library approach. Materials and methods Soil sampling The soil sample was collected below a dead seal, in Cape Evans, McMurdo Dry Valley, Antarctica, 771380 1000 S and 1661250 0400 E, in January 1995. No vegetation was observed near the place of sample B.V. Shravage et al. collection. The sample was collected in sterilized polyethylene bag, placed in ice and stored at 70 1C until further processing. The air temperature at the time of collection was +5 1C. Isolation of DNA Total community DNA was extracted from 1 g of soil sample using protocol III as described earlier with minor modifications (Yeates et al., 1997). In brief, the soil sample was resuspended in extraction buffer (100 mM Tris–Cl (pH 8.0), 100 mM Na2EDTA (pH 8.0), 1.5 M NaCl) and incubated overnight at 37 1C by shaking at 150 rpm with lysozyme (200 mg/ ml) and Protenase K (100 mg/ml). The step that includes the disruption of cells using glass beads was omitted. The same sample was processed for the DNA extraction again. The sample was processed for third extraction and visualized for any DNA by electrophoresis on 0.7% agarose gel and ethidium bromide staining. The DNA was pooled from first and second the extraction steps and used for PCR amplification of 16S rDNA gene. Polymerase chain reaction (PCR) and generation of SSU rDNA clone library Eubacterial SSU rDNA gene universal primers 16F27N (50 -CCAGAGTTTGATCMTGGCTCAG-30 ) and 16R1525XP (50 -TTCTGCAGTCTAGAAGGAGGTGTWT CCAGCC-30 ) (Brosius et al., 1978) were used to amplify the 16S rDNA gene from total community DNA. All PCR reactions were performed in a PE 9700 thermal cycler (Applied Biosystems, Inc., Foster City, CA) under following conditions: Initial denaturation at 94 1C for 2 min followed by 35 cycles of 94 1C for 30 s, 64 1C for 1 min and 72 1C for 1 min, with an additional extension step at 72 1C for 10 min. Reaction mixture of 50 ml contained 50 ng of DNA template, 25 pm of each primer, 1 ml of 10 mM deoxynucleoside triphosphates (Amersham biosciences) 5 ml of 10X ThermoPol reaction buffer (20 mM Tris–HCl (pH 8.8), 10 mM KCl, 10 mM (NH4)2SO4, 2 mM MgSO4, 0.1% Triton X-100) and 1U Taq DNA polymerase (New England Biolabs). PCR products were run on 0.8% agarose gel along with standard molecular weight marker, stained with ethidium bromide solution and visualized for 1.5 kbp product under UV transilluminator. The amplified rDNA was cloned in pGEM-T vector (Promega Corporation, USA) in accordance with the manufacturer’s instructions. The presence of ammonia oxidizing bacteria was determined by PCR using the conserved primers for the gene encoding the active site subunit of ammonia monoxygenase ARTICLE IN PRESS Molecular microbial diversity of a soil sample and detection of ammonia oxidizers from Antarctica (amoA). The primer combination consisted of amoA-1F and amoA-2R which has been proved most reliable in earlier studies (Rotthauwe et al., 1997). The forward primer used amoA-1F (50 -GGGGTTTC TACTGGTGGT-30 ) targets a stretch corresponding to positions 332–349 and the reverse primer used (amoA-2R (50 -CCCCTCKGSAAAGCCTTCTTC-30 ) targets a stretch corresponding to positions 802– 822of the open reading frame for the amoA gene sequence of Nitrosomonas europaea (McTavish et al., 1993). PCR reactions were as described above except that the annealing temperature was 60 1C for 1 min 30 s. Nucleotide sequencing of cloned SSU rDNA genes Crude DNA lysates of clones were used for PCR amplification of the clones using vector specific primers. Resulting clones were screened by PCR using vector specific primers. The nucleotide sequence of the cloned SSU rDNA gene was determined using vector specific primers and sequenced directly on ABI PRISM 310 Genetic Analyzer (Applied Biosystems, Inc.) to obtain at least 500 bp from 50 end of SSU rDNA gene. This stretch contains three hyper variable regions, three variable regions and three constant regions that help in the discrimination of closely related species. Sequence and phylogenetic analyses All the sequences were checked for chimera formation by using CHECK_CHIMERA software of the ribosomal database project (Maidak et al., 1997). Analysis of the cloned SSU rDNA gene sequences was performed using basic local alignment search tool (BLAST) (Altschul et al., 1997) at NCBI server. Phylogenetic analyses were restricted to 482 nucleotide positions that were unambiguously alignable in all sequences. A phylogenetic analysis by neighbor joining method was done using the PHYLIP version 3.63 (Felsenstein, 1989). The number of clones representing a blast hit was considered as clones representing a species and species richness, which is the number of species in the assemblage, was calculated using the default parameters provided in EcoSim 7.0 software (Gotelli and Entsminger, 2001). Results and discussion The existing procedure (Yeates et al., 1997) was modified slightly to get good quality high molecular 17 weight DNA from soil. Our extraction procedure yielded 25–30 mg of good quality DNA from 1 g of soil, which was used for PCR without further purification. 1.5 kb region of almost complete SSU rDNA gene was amplified using eubacteria specific primers. To minimize the errors the PCR was done in triplicates and the PCR products were pooled before cloning into pGEMT-easy vector. A total of 86 clones were obtained. The insert DNA from clones was PCR-amplified using vector specific primers and sequenced. The sequences had at least 500 nucleotides from 50 -terminus of 16S rRNA gene. This stretch contains three hyper variable regions, three variable regions and three conserved regions. Analysis of the cloned SSU rDNA gene sequences was performed using the BLAST at NCBI server. None of sequences was detected as potential CHIMERA. Table 1 lists the clones along with percentage similarity with nearest blast hits. The percentage similarity with clone and its closest blast hits ranged from 85% to 99% (Table 1). A phylogenetic tree was drawn which clearly shows the affiliation of different SSU rDNA clones with its closest BLAST hits (Fig. 1). The clones were distributed in to three main clusters, viz. proteobacter, Cytophaga/Flavobacterium/Bacteroides (CFB) and high GC/Deinococcus–Thermus group. The clone sequences showed similarity to different subclasses of a, b, g Proteobacteria, CFB group, High GC gram positive and Thermus–Deinococcus groups. Nine of the clones had more than 97% similarity to the closest BLAST hits and the rest of the clones had less or equal similarity to BLAST hits. This suggests the presence of a large number of operational taxonomic units (OTUs) among the clones. In the soil sample studied we found that some clones which showed their closest relation to Nitrospira and Nitorsomonas spp. As these bacteria may be involved in ammonia oxidation process, their functionality was checked by PCR for the presence of ammonia monoxygenase gene (amoA). The PCR was done with primers amoA-1F and amoA-2R resulted in 491 bp PCR product (Fig. 5) that confirmed the presence of amoA gene in Antarctic soil sample. CFB group Cytophagales can be highly abundant in the costal pelagic zone of Antarctica. They constitute 20–70% of the bacterial biomass in various seawater samples. They have major roles to play in mineralization of macromolecules to micronutrients (Glockner et al., 1999). 53.5% of the clones from this soil sample showed similarity to CFB group. Out ARTICLE IN PRESS 18 B.V. Shravage et al. Table 1. Sl. No. List of the SSU rDNA clones along with their accession numbers and BLAST hits Name of the clone Acc. no. of clones Closest blast his Cytophaga–Flavobacterium–Bacteroidetes 1 bh1.2 AF417864 Cytophaga sp. B12 2 bh1.19 AF417871 Cytophaga sp. B12 3 bh2.4 AF417881 Cytophaga sp. B12 4 bh2.54 AF417890 Cytophaga sp. B12 5 bh2.59 AF447178 Cytophaga sp. B12 6 bh2.65 AF417894 Cytophaga sp. B12 7 bh3.20 AF417899 Cytophaga sp. B12 8 bh3.37 AF417901 Cytophaga sp. B12 9 bh3.63 AF417903 Cytophaga sp. B12 10 bh5.7 AF417916 Cytophaga sp. B12 11 bh5.18 AF417919 Cytophaga sp. B12 12 bh5.13 AF447180 Cytophaga sp. B12 13 bh5.49 AF419200 Cytophaga sp. B12 14 bh6.11 AF419207 Cytophaga sp. B12 15 bh6.22 AF419208 Cytophaga sp. B12 16 bh7.22 AF420427 Cytophaga sp. B12 17 bh6.44 AF419211 Cytophaga sp. B12 18 bh6.45 AF419212 Cytophaga sp. B12 19 bh6.53 AF419214 Cytophaga sp. B12 20 bh6.61 AF419217 Cytophaga sp. B12 21 bh7.10 AF419280 Cytophaga sp. B12 22 bh4.59 AF417911 Cytophaga sp. 4301-10/1 23 bh2.35 AF417885 Vitellibacter vladivostokensis 24 bh3.26 AF417900 Vitellibacter vladivostokensis 25 bh1.33 AF417873 Aequorivita lipolytica Y10-2T 26 bh8.7 AF419285 Aequorivita crocea Y12-2T 27 bh8.55 AF419290 Flavobacterium sp. GWS-SE-H171 28 bh1.8 AF417865 Flavobacterium sp. V4.MS.12 29 bh1.44 AF417893 Flexibacter sp. OUB39 30 bh8.6 AF419284 Subsaxibacter broadyi strain P7 31 bh8.17 AF419286 Antarctic bacterium R-9217 32 bh4.63 AF419193 Antarctic bacterium R-7933 33 bh5.22 AF419195 Marine bacterium KMM 3937 34 bh1.62 AF417880 Bacterium Km4 35 bh8.26 AF419287 Unidentified bacterium 36 bh2.10 AF417882 Bacteroidetes bacterium GMDJE10E6 37 bh2.14 AF417883 Bacteroidetes bacterium GMDJE10E6 38 bh2.16 AF417884 Bacteroidetes bacterium GMDJE10E6 39 bh5.9 AF417917 Bacteroidetes bacterium GMDJE10E6 40 bh5.45 AF419199 Bacteroidetes bacterium GMDJE10E6 41 bh2.41 AF417886 Bacteroidetes bacterium GMDJE10E6 42 bh2.58 AF417892 Bacteroidetes bacterium GMDJE10E6 43 bh4.2 AF417902 Bacteroidetes bacterium MO48 44 bh4.20 AF417906 Bacteroidetes bacterium MO54 45 bh4.10 AF417904 Uncultured Bacteroidetes bacterium 46 bh6.8 AF419206 Uncultured Bacteroidetes bacterium clone ML602J-37 Alpha proteobacter 1 bh3.3 AF417896 Roseobacter sp. ANT9270 2 bh7.13 AF419281 Roseobacter sp. ANT9270 3 bh7.15 AF419282 Roseobacter sp. ANT9270 4 bh4.32 AF417907 Sphingomonas baekryungensis 5 bh5.52 AF419202 Uncultured bacterium clone DC-5 Acc. no. of Similarity of SSU rDNA sequence 50 end of the closest blast hit clone (X500 bp) to its closest match (%) AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF125327 AF536383 AF125327 AF125327 AF125327 AJ542652 AB071382 AB071382 AY027805 AY027806 AY332172 AJ244703 AB058913 AY693999 AJ441008 AJ440987 AF536386 AF367848 AJ786810 AY162091 AY162091 AY162091 AY162091 AY162091 AY162091 AY162091 AY553119 AY553122 AY701441 AF507870 95 95 93 96 97 93 96 94 96 91 94 97 97 94 95 94 96 90 96 97 97 87 92 92 92 96 93 90 93 94 97 97 89 93 94 88 87 88 87 90 85 86 88 93 92 93 AY167260 AY167260 AY167260 AY608604 AY529883 96 96 96 98 96 ARTICLE IN PRESS Molecular microbial diversity of a soil sample and detection of ammonia oxidizers from Antarctica 19 Table 1. (continued ) Sl. No. 6 Beta 1 2 3 4 5 Name of the clone bh5.33 Proteobacter bh1.16 bh1.36 bh8.1 bh8.2 bh5.50 Acc. no. of Similarity of SSU rDNA sequence 50 end of the closest blast hit clone (X500 bp) to its closest match (%) Acc. no. of clones Closest blast his AF419197 Uncultured marine eubacterium HstpL100 AF159651 98 AF417869 AF417875 AF419283 AF420429 AF447181 Nitrosospira sp. Nsp65 Nitrosomonas cryotolerans Uncultured bacterium clone KD4-7 Uncultured bacterium clone 234ds5 Uncultured earthworm cast bacterium clone c286 AY123813 AF272423 AY218644 AY212681 AY154632 95 94 96 97 97 Uncultured Psychrobacter sp. clone GAMMA4A Uncultured Psychrobacter sp. Clone GAMMA4A Uncultured Psychrobacter sp. Clone GAMMA4A Uncultured Psychrobacter sp. Clone GAMMA4A Uncultured Psychrobacter sp. clone GAMMA4A Gamma proteobacterium KT0813 Gamma proteobacterium KT0813 Gamma proteobacterium KT0813 Gamma proteobacterium KT0813 Gamma proteobacterium KT0813 Gamma proteobacterium KT0813 Chromohalobacter sp. MAN K24 Psychrobacter okhotskensis Psychrobacter okhotskensis Psychrobacter okhotskensis Psychrobacter fozii Psychrobacter sp. HS5323 Psychrobacter sp. p3C Psychrobacter sp. IC008 Psychrobacter urativorans Rubrobacter radiotolerans Marinobacter sp. MED106 Arctic sea ice bacterium ARK9987 Uncultured bacterium clone ARKDMS-9 AY494610 98 AY494610 96 AY494610 96 AY494610 97 AY494610 97 AF235130 AF235130 AF235130 AF235130 AF235130 AF235130 AB166934 AB094794 AB094794 AB094794 AY771717 AY443042 AJ495805 U85875 AJ609555 U65647 AY136121 AF468405 AF468252 93 92 96 93 96 96 93 99 95 98 99 95 99 98 97 93 94 99 93 Rubrobacteridae bacterium Ellin5415 Desulfotomaculum aeronauticum AY673142 AY703033 96 95 Uncultured bacterium clone B-42 Uncultured bacterium clone B-42 Deinococcus sp. AA63 AY676482 AY676482 AJ585986 87 87 97 Gamma proteobacter 1 bh1.1 AF417862 2 bh1.11 AF417867 3 bh4.60 AF417912 4 bh4.66 AF417914 5 bh6.55 AF419215 6 bh1.37 AF417878 7 bh1.56 AF417879 8 bh2.44 AF417887 9 bh4.12 AF417905 10 bh4.40 AF417909 11 bh4.62 AF417913 12 bh4.45 AF417910 13 bh3.1 AF417895 14 bh5.19 AF419194 15 bh6.31 AF419209 16 bh3.5 AF417898 17 bh5.2 AF417915 18 bh2.51 AF417889 19 bh5.29 AF419196 20 bh5.53 AF419203 21 bh3.17 AF417897 22 bh3.31 AF447179 23 bh6.39 AF419210 24 bh8.50 AF419288 High GC gram + 1 bh7.44 AF420428 2 bh4.3 AF417908 Dienococcus–Thermus 1 bh6.6 AF419205 2 bh6.58 AF419216 3 bh8.52 AF419289 of 46 clones 22 belonged to Cytophaga sp. with 87–97% similarity in the BLAST. The intra clone similarity was ranging between 59% and 91%, which shows high diversity among Cytophaga sp. in the soil sample. Seven clones showed 85–90% similarity to Bacteroidetes bacterium isolate GMDJE10E6 and had 82–99% intra clone similarity (data not shown); two of the clones belonged to Bacteroidetes bacterium clone MO48 and two of the Bacteroidetes were showing similarity to uncultured clones. The clones representing Vitellibacter vladivostokensis, Aequorivita lipolytica, Flavobacterium sp., ARTICLE IN PRESS 20 B.V. Shravage et al. bh5.2 bh4.66 bh5.19 bh4.60 bh1.11 bh1.1 bh6.55 Uncultured Psychrobacter sp. clone G Psychrobacter fozii Psychrobacter sp. HS5323 Psychrobacter okhotskensis Arctic sea ice bacterium ARK9987 bh3.1 bh6.31 bh5.29 Psychrobacter sp. IC008 bh2.51 Psychrobacter sp. p3C Psychrobacter urativorans bh3.5 bh5.53 Chromohalobacter sp. MAN K24 bh4.45 bh3.31 Marinobacter sp. MED106 bh8.50 Uncultured bacterium clone ARKDMS bh1.16 bh1.36 Nitrosomonas cryotolerans Nitrosospira sp. Nsp65 bh8.1 Uncultured bacterium clone KD4-7 Uncultured bacterium clone 234ds5 bh7.15 bh3.3 bh7.13 Roseobacter sp. ANT9270 Uncultured earthworm cast bacterium Uncultured bacterium clone DC-5 Uncultured marine eubacterium HstpL bh5.50 bh5.52 bh5.33 S. baekryungensis bh4.32 bh6.39 bh1.56 bh4.62 bh4.40 bh2.44 Gamma proteobacterium KT0813 bh4.12 bh1.37 bh8.2 bh7.44 bh5.7 bh5.22 bh3.37 bh5.18 bh5.13 bh1.2 bh6.45 bh1.19 bh3.20 bh6.53 bh6.44 bh2.65 Cytophaga sp. B12 bh6.61 bh6.22 bh5.49 bh2.59 bh1.44 bh7.10 bh4.63 bh3.63 bh7.22 bh2.54 bh2.4 bh6.11 Marine bacterium KMM 3937 Antarctic bacterium R-7933 Flexibacter sp. OUB39 bh8.26 bh8.6 Subsaxibacter broadyi strain P7 Antarctic bacterium R-9217 bh8.17 Unidentified bacterium bh8.7 Aequorivita crocea Y12-2T Aequorivita lipolytica Y10-2T bh8.55 Vitellibacter vladivostokensis Bacterium Km4 Flavobacterium sp. GWS-SE-H171 bh1.62 bh2.35 bh3.26 bh1.33 bh1.8 bh4.59 Cytophaga sp. 4301-10/1 Flavobacterium sp. V4.MS.12 bh4.2 bh4.3 bh5.9 bh2.14 bh4.10 bh2.58 bh2.41 bh2.10 bh2.16 bh6.8 bh5.45 bh4.20 Uncultured Bacteroidetes bacterium Bacteroidetes bacterium GMDJE10E6 Uncultured Bacteroidetes bacterium c Bacteroidetes bacterium MO54 Bacteroidetes bacterium MO48 bh6.58 bh6.6 Uncultured bacterium clone B-42 Deinococcus sp. AA63 bh8.52 Desulfotomaculum aeronauticum Rubrobacteridae bacterium Ellin5415 bh3.17 Rubrobacter radiotolerans Halobacterium salinarum Proteobacter Group CytophagaFlavobacteriumBacteroidetes Group High GC and DeinococcusThermus Group Figure 1. Neighbor joining tree representing the affiliation of the SSU rDNA clones to their closest related sequence. Halobacterium salinarum is used as an out-group. ARTICLE IN PRESS Molecular microbial diversity of a soil sample and detection of ammonia oxidizers from Antarctica Flexibacter sp., Subsaxibacter broadyi were also found in the soil sample analyzed (Fig. 2). These clones shared 92–97% similarity to their closest relatives. Such observations with less than 95% similarity to 16S rDNA gene sequences available in the GenBank indicate the presence of novel and uncharacterized bacterial lineage from Antarctic soil. The soil sample from our study had large number of members of CFB group and showed similarity to the microbial flora of SIMCO (Brown and Bowman, 2001) and differed completely from the earlier study on soil sample form Antarctica (Shivaji et al., 2004). Proteobacter group Nearly 40% of the clones from the library belonged to Proteobacteria group (Fig. 3). Out of 35 clones six, five and 24 clones belonged to a, b and g subgroups of proteobacteria, respectively. In our study, gamma proteobacter subgroup constitutes 28% of the clones, which is similar to the earlier observations of Shivaji et al. (2004), wherein 32% of the clones belonged to gamma proteobacter subgroup. Six of the clones showed similarities to gamma proteobacterium isolate KT0813, and shared 73–97% intra clone similarities (data not shown). Similarly five of the clones showed BLAST hit to uncultured Psychrobacter sp. clone GAMMA4A and shared 94–97% intra clone similarities. The clones representing Roseobacter sp., Sphingomonas baekryungensis, Nitrosospira sp., Nitrosomonas cryotolerans, Chromohalobacter sp., Psychrobacter spp., Rubrobacter radiotolerans, Marinobacter sp. have also been found in the library. Ammonia oxidizers in Antarctica soil Members of gamma proteobacteria group belonging to genera Psychrobacter and Marinobacter have been isolated (Bowman et al., 2000a, b) and clones representing their rDNA detected in earlier studies (Brambilla et al., 2001). The gene encoding the active site subunit of ammonia monoxygenase (amoA) has been extensively used as a molecule for cultivation-independent analysis of ammonia oxidizer diversity (Mendum et al., 1999; Purkhold et al., 2000; Purkhold et al., 2003; Rotthauwe et al., 1997). Beta subgroup proteobacteria contained sequences that showed 94–95% homologies to Nitrospira and Nitrosomonas. These organisms are known as ammonia oxidizers, which play a central role in recycling nitrogen (Purkhold et al., 2003). Their presence was further confirmed by the presence of 491 bp PCR product for amoA gene (Fig. 5) using the primers designed specific to the ammonia oxidizers as described earlier (Rotthauwe et al., 1997). The beta proteobacteria were represented by three clone sequences with homologies to uncultured clones. This shows the complex diversity of Antarctic bacteria. Cytophaga-Flavobacterium-Bacteroidetes Group 25 20 No. of Clones 21 15 10 5 Vi Cy to Cy to ph ph ag te a a g lli sp ba a s .B p ct Ae . er 43 12 qu 01 vl or ad -1 iv iv it os 0/1 Ae a lip to Fl ke qu ol av ns yt or ob is ic iv ac a i t Y1 te a 0Fl rium croc av ea 2T ob sp. Y1 ac G 2W te 2 riu SSE T m Su Fl s H bs e p. ax xib V4 171 a ib .M ac cte S. r t 12 An er b sp. ro O ta U ad rc B3 An tic b yi s tra 9 ta ac rc i t n tic eri M P7 ar ba um in Rct e er ba iu 921 ct m 7 er Riu 79 m Ba 33 K ct M er Ba M3 U oi ct ni de 9 e d te riu 37 en s tif m Ba bac ie K d te ct U riu ba m4 er nc ct oi m ul er B d G tu et ac iu M es re m U t e D d n r b J o c ac Ba E1 ul id te tu et ct 0 r E6 es er re iu oi d de Ba bac m M te te c O t r sb er 48 oi ium ac de te M te riu O sb 5 m ac 4 cl te on r iu e M m L6 02 J37 0 BLAST hits Figure 2. Representation of the clones belonging to Cytophaga—Flavobacterium–Bacteroidetes group. ARTICLE IN PRESS 22 B.V. Shravage et al. Proteobacter Group 7 No. of Clones 6 5 4 3 2 1 U U Sp Ro s hi eob n a nc g n o ct ul tu cult mo er s re ur na p. d m e d b s b a AN ar T in act ekr 92 e e er 7 y ub ium ung 0 en ac c s Ni teri lone is u t U U nc Nit ros m H DC nc o r ul s -5 s os ul tu o pir tpL U tu U red nc red mon a s 10 nc p 0 u b ul ear ltur act as c . N tu s re thw ed b eriu ryo p65 d o t Ps rm act m c ole lo ra e yc c hr ast rium ne ns ob ba c KD G acte cte lon 4-7 am r s riu e23 m m 4d Ch a p p. c c s ro ro lon lone 5 t eG c m oh eob 2 A 8 al ac M 6 o Ps ba teri MA yc cte um 4 hr r s K A o b p . T0 ac M 81 te r AN 3 Ps Psy okh K2 yc ch ots 4 hr ob roba ken s Ps acte cte is yc r s r f o h z Ps ro p. H ii b y Ps c h r a c t S 5 3 yc ob er 23 s a h Ru rob cter p. p 3C br ac s p ob ter .IC ac u M A 0 r U 0 nc rcti arin ter ativ 8 ul c s ob rad or tu e a i a ot ns re a i ol c cte d er ba e b r s a ct ac p. er M ns te riu ED iu m m 1 cl on AR 06 e A K9 RK 98 D 7 M S9 0 BLAST hits Figure 3. Representation of the clones belonging to Proteobacter group. 100 Estimated species richness Abundance Average Diversity 10 Median Diversity 95% Conf. Low 95% Conf. High 1 1 5 9 13 17 21 25 29 33 37 41 45 Number of clones Figure 4. Species richness estimate curves derived from SSU rDNA clone library data of Antarctica soil sample. Thermophiles in Antarctica soil Thermophillic microorganisms from Antarctica have been reported from hot soils of Mount Erebus, Ross Island (Boyd and Boyd, 1963). Antarctic soil is known to harbor thermophillic strains in the northern Victoria Land but not in McMurdo Dry Valleys (Logan et al., 2000). In the earlier studies on soil sample analyzed (Shivaji et al., 2004), the presence of this group was not reported. Surprisingly, from our study two clones bh8.53 and bh4.3 shared their closest relation (97% and 95%, respectively) with Deinococcus and Desufomaculum aeronauticum. However, their presence has to be supported by culture-based studies to support the theory of thermophillic microorganisms from Antarctic soils. The analyses of species richness for the SSU rDNA clones generated from Antarctica soil sample revealed high diversity levels (Fig. 4). The average diversity was falling between the 95% confident values generated for the sample. In the SSU rDNA clone library study, some genes were represented by single clone while some genera were represented by large number of clones. Such observations have been reported earlier in studies that were also based on SSU rDNA clone library approach (Schmidt et al., 1991; Shivaji et al., 2004). These observations may be attributed to several reasons ARTICLE IN PRESS Molecular microbial diversity of a soil sample and detection of ammonia oxidizers from Antarctica and are guided by many factors (Amann et al., 1995). Antarctica is a hotspot for those who are interested in life at extreme environments. SSU rDNA clone library analysis has shed light on those aspects where once it was thought life could not exist in extreme conditions. Our study revealed high microbial diversity existing in such environments. We discovered SSU rDNA clones of bacteria like Nitrosomonas and Nitrosospira spp. that are known to play roles in ammonia oxidization, but these clones had only 94–95% similarity to the closest blast hits. As it was very difficult to assign a functional role to these clones as similarities to it’s nearest cultured neighbor were distant, we checked for the presence of functional gene amoA which is required for ammonia oxidation using amoA specific primers which has been successfully used earlier in similar studies. We confirmed the presence of amoA functional gene in Antarctica soil by the PCR amplication, which produced 491 bp product (Fig. 5). Also it is now a known fact that PCR primers influence the sequence diversity within SSU rDNA gene libraries (Marchesi et al., 1998). Also there are many factors like PCR cycling parameters and the amount of DNA template used in PCR reaction, which may affect the coverage and hence overall diversity in uncultured 16S rDNA library approach. 23 We strongly believe that combination of various methods and larger sampling would help to resolve the biases in studies involving molecular methods to determine the diversity of microorganisms. Further studies will also help in understanding the survival and role of microorganisms in extreme environments. The soil sample studied was collected below a dead seal with an interest to find out the possibility of microbes, which may be involved in recycling of macromolecules to microelements in harsh environments like Antarctica. However the possibility of microflora originating from the dead animal could not be ruled out. From industrial and pharmaceutical point of view, such extreme environments harbor microorganisms that could be used as potential source of novel enzymes and secondary metabolites/antibiotics. This was an effort to study uncultured diversity of Antarctic soil sample using SSU rDNA gene library based method. Some of the clones, belonging to bacteroidetes group, had similarity values less than 90% to their closest blast hits, which indicate the presence of new lineages in Antarctic soil. However, the presence of ammonia oxidizers is significant from the point of nitrogen recycling and the presence of thermophiles needs further investigation. References Figure 5. PCR amplification of the specific 491 bp fragment of the amoA gene from Antarctic soil. M, 1Kb+ DNA ladder (Invitrogen); lane1, amoA gene PCR product. Altschul, S.F., Madden, T.L., Schaffer, A.A., Zhang, J., Zhang, Z., Miller, W., Lipman, D.J., 1997. 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