Contribution to nitrogen fixation and soil fertility by photosynthetic bacteria

Summary The nitrogen fixation ability ofRhodopseudomonas capsulatus (a member of the photosynthetic bacteria) has been investigated. This organism can fix N₂ most effectively under illuminated anaerobic conditions. However, in mixed culture in symbiotic association with heterotrophic bacteria, this microorganism using pyruvic acid excreted by the heterotrophs is capable of fixing nitrogen even under an apparent aerobic environment. It has been demonstrated that some correlation exists between the growth of photosynthetic bacteria and the reproduction of the rice plant. Compared to the mineral fertilizer, application of photosynthetic bacteria at the reproductive stage of rice plants increased the yield of grain. This was confirmed by the fact that the root system of rice is capable of absorbing amino acids and nucleic acids excreted by photosynthetic bacteria. Uracil and proline have the most influence on rice reproduction. This is also true for tomato plants. Many toxic molecules such as hydrogen sulfide, amines, etc. are found in soil. They are metabolized by photosynthetic bacteria, which contributes to the detoxication of soil. Such findings were extended to the purification of polluted waste waters from industry and domestic sources,etc. It can be concluded that photosynthetic bacteria contribute very significantly to soil fertility and improvement of the plant growth condition.     

Pulsed-field gel electrophoresis fingerprinting for identification of Azospirillum species

Pulsed-field gel electrophoresis (PFGE) was used to obtain macrorestriction fingerprints of restriction enzyme-cut DNA of natural isolates of Azospirillum spp. Metabolic profiles, along with other phenotypic characteristics, were compared with these fingerprints to differentiate among the azospirilla isolates. A wide diversity of phenotypes (e.g., colony color, motility, and accumulation of poly--hydroxybutyrate granules) was observed among the natural isolates of azospirilla. PFGE revealed that TCTAGA, the sequence recognized by Xba1, is rare in the genome of azospirilla. The PFGE fingerprint revealed that azospirilla associated with different crops have a very similar genetic background. PFGE fingerprints were more consistent in the identification of azospirilla isolates from specific hosts than the metabolic fingerprints. For further differentiation at strain level, metabolic, physiological, and morphological profiles provide additional information.Journal No. J-2920 of the Montana Agricultural Experiment Station.     

Occurrence of Horizontal Gene Transfer of PIB-type ATPase Genes among Bacteria Isolated from the Uranium Rich Deposit of Domiasiat in North East India

Uranium (U) tolerant aerobic heterotrophs were isolated from the subsurface soils of one of the pre-mined U-rich deposits at Domiasiat located in the north-eastern part of India. On screening of genomic DNA from 62 isolates exhibiting superior U and heavy metal tolerance, 32 isolates were found to be positive for P_IB-type ATPase genes. Phylogenetic incongruence and anomalous DNA base compositions revealed the acquisition of P_IB-type ATPase genes by six isolates through horizontal gene transfer (HGT). Three of these instances of HGT appeared to have occurred at inter-phylum level and the other three instances indicated to have taken place at intra-phylum level. This study provides an insight into one of the possible survival strategies that bacteria might employ to adapt to environments rich in uranium and heavy metals.     

Molecular and functional characteristics, growth promoting effect and persistence of selected parent isolates and streptomycin resistant derivatives of rice rhizobacteria

Molecular and functional characteristics of seven azospirilla and five phosphorus solubilizing bacteria (PSB) isolates of rice rhizosphere, growth promotion ability of two efficient strains, Azospirillum amazonense A10 (MTCC4716) and Bacillus megaterium P5 (MTCC4714) and their persistence based on streptomycin resistant derivatives (SRD), were determined. SDS-PAGE and isozyme banding patterns of the isolates were used to arbitrarily group the azospirilla into 4 and PSB into 3 clusters and as markers to ascertain their identity. The azospirilla produced 2.0 to 10.5 ppm of IAA like substances and showed nitrogenase activity of 0.02 to 3.55 nmole C2H4/hr/ml of pure culture. PSB isolates produced 7.8 to 15.0 ppm IAA like substances and 20 to 128 ppm soluble P. Induction of resistance to streptomycin resulted in changes of these properties. Co-inoculation of rice with SRD A10 and SRD P5 and their parental strains in separate treatments enhanced grain yield over control by 31 and 12.4%, respectively. Nitrogenase activity of rice roots under SRD co-inoculated treatment was higher (4.16 nmole C2H4/hr/hill) than that-under parental strains co-inoculated treatment (3.76 nmole C2H4/hr/hill). SDS-PAGE profile and population count of the strains confirmed their establishment in rice rhizosphere and persistence over a year after inoculation.     

Diversity and functional traits of culturable microbiome members,including cyanobacteria in the rice phyllosphere

The diversity and abundance of culturable microbiome members of the rice phyllosphere was investigated using cv. Pusa Punjab Basmati 1509. Both diversity and species richness of bacteria were significantly higher in plants in pots in a semi‐controlled environment than those in fields. Application of fertilisers reduced both diversity and species richness in field‐grown plants under a conventional flooded system of rice intensification (SRI) and in dry‐seeded rice (DSR) modes. Sequence analyses of 16S rDNA of culturable bacteria, those selected after amplified ribosomal DNA restriction analysis (ARDRA), showed the dominance of α‐proteobacteria (35%) and actinobacteria (38%); Pantoea, Exiguobacterium and Bacillus were common among the culturable phyllospheric bacteria. About 34% of 83 culturable bacterial isolates had higher potential (>2 μg·ml^?1) for indole acetic acid production in the absence of tryptophan. Interestingly, the phyllosphere bacterial isolates from the pot experiment had significantly higher potential for nitrogen fixation than isolates from the field experiment. Enrichment for cyanobacteria showed both unicellular forms and non‐heterocystous filaments under aerobic as well as anaerobic conditions. PCR‐DGGE analysis of these showed that aerobic and anaerobic conditions as well as the three modes of cultivation of rice in the field strongly influenced the number and abundance of phylotypes. The adaptability and functional traits of these culturable microbiome members suggest enormous diversity in the phyllosphere, including potential for plant growth promotion, which was also significantly influenced by the different methods of growing rice.     

Aerobic heterotrophic bacteria and petroleum-utilizing bacteria from cow dung and poultry manure

In this study, enumeration and identification of total aerobic heterotrophic bacteria and petroleum-utilizing bacteria as well as the degradative potential of petroleum-utilizing bacterial isolates were carried out. The average counts of total aerobic heterotrophic bacteria in cow dung and poultry manure were 74.25 × 10⁵ c.f.u. g⁻¹ and 138.75 × 10⁵ c.f.u. g⁻¹ respectively. Acinetobacter sp, Bacillus sp, Pseudomonas sp, and Serratia spp. occurred as aerobic heterotrophs in both cow dung and poultry manure. However, Alcaligenes spp. occurred only in cow dung while, Flavobacterium sp, Klebsiella sp, Micrococcus sp, and Nocardia spp. occurred only in poultry manure as aerobic heterotrophs. The average counts of petroleum-utilizing bacteria in cow dung and poultry manure were 9.25 × 10⁵ c.f.u. g⁻¹ and 17.25 × 10⁵ c.f.u. g⁻¹ respectively. Pseudomonas spp. occurred as petroleum utilizer in both cow dung and poultry manure. However, Bacillus spp. occurred only in cow dung while Acinetobacter spp. and Micrococcus spp. occurred only in poultry manure as petroleum utilizers. Relative abundance of petroleum utilizers in total aerobic heterotrophs ranged from 6.38% to 20.00% for cow dung and from 9.38% to 17.29% for poultry manure. Introduction of pure cultures of petroleum-utilizing bacteria from cow dung and poultry manure into sterile oil-polluted soil revealed oil degradation in one week period.     

Molecular and phenotypic characterization of potential plant growth-promoting <Emphasis Type="Italic">Pseudomonas</Emphasis> from rice and maize rhizospheres

In this study, Pseudomonas species were isolated from the rhizospheres of two plant hosts: rice (Oryza sativa cultivar Pathum Thani 1) and maize (Zea mays cultivar DK888). The genotypic diversity of isolates was determined on basis of amplified rDNA restriction analysis (ARDRA). This analysis showed that both plant varieties selected for two distinct populations of Pseudomonas. The actual biocontrol and plant promotion abilities of these strains was confirmed by bioassays on fungal (Verticillum sp., Rhizoctonia solani and Fusarium sp.) and bacterial (Ralstonia solanacearum and Bacillus subtilis) plant pathogens, as well as indole-3-acetic acid (IAA) production and carbon source utilization. There was a significant difference between isolates from rice and maize rhizosphere in terms of biological control against R.  solanacearum and B.  subtilis. Interestingly, none of the pseudomonads isolated from maize rhizosphere showed antagonistic activity against R.  solanacearum. This study indicated that the percentage of pseudomonad isolates obtained from rice rhizosphere which showed the ability to produce fluorescent pigments was almost threefold higher than pseudomonad isolates obtained from maize rhizosphere. Furthermore, the biocontrol assay results indicated that pseudomonad isolated from rice showed a higher ability to control bacterial and fungal root pathogens than pseudomonad isolates obtained from maize. This work clearly identified a number of isolates with potential for use as plant growth-promoting and biocontrol agents on rice and maize.     

Nitrogen-Fixing (Acetylene Redution) Activity and Population of Aerobic Heterotrophic Nitrogen-Fixing Bacteria Associated with Wetland Rice

Nitrogen-fixing activity associated with different wetland rice varieties was measured at various growth stages by an in situ acetylene reduction method after the activities of blue-green algae (cyanobacteria) in the flood water and on the lower portion of the rice stem were eliminated. Nitrogen-fixing activities associated with rice varieties differed with plant growth stages. The activities increased with plant age, and the maximum was about at heading stage. The nitrogen fixed during the whole cropping period was estimated at 5.9 kg of N per ha for variety IR26 (7 days) and 4.8 kg of N per ha for variety IR36 (95 days). The population of aerobic heterotrophic N₂-fixing bacteria associated with rice roots and stems was determined by the most-probable-number method, using semisolid glucose-yeast extract and semisolid malate-yeast extract media. The addition of yeast extract to the glucose medium increased the number and activity of aerobic heterotrophic N₂-fixing bacteria. The glucose-yeast extract medium gave higher counts of aerobic N₂-fixing bacteria associated with rice roots than did the malate-yeast extract medium, on which Spirillum-like bacteria were usually observed. The lower portion of the rice stem was also inhabited by N₂-fixing bacteria and was an active site of N₂ fixation.     

Isolation of hydrogen-producing bacteria from granular sludge of an upflow anaerobic sludge blanket reactor

H₂-producing bacteria were isolated from anaerobic granular sludge. Out of 72 colonies (36 grown under aerobic conditions and 36 under anaerobic conditions) arbitrarily chosen from the agar plate cultures of a suspended sludge, 34 colonies (15 under aerobic conditions and 19 under anaerobic conditions) produced H₂ under anaerobic conditions. Based on various biochemical tests and microscopic observations, they were classified into 13 groups and tentatively identified as follows: From aerobic isolates,Aeromonas spp. (7 strains),Pseudomonas spp. (3 strains), andVibrio spp. (5 strains); from anaerobic isolates,Actinomyces spp. (11 strains),Clostridium spp. (7 strains), andPorphyromonas sp. When glucose was used as the carbon substrate, all isolates showed a similar cell density and a H₂ production yield in the batch cultivations after 12h (2.24–2.74 OD at 600 nm and 1.02–1.22 mol H₂/mol glucose, respectively). The major fermentation by-products were ethanol and acetate for the aerobic isolates, and ethanol, acetate and propionate for the anaerobic isolates. This study demonstrated that several H₂ producers in an anaerobic granular sludge exist in large proportions and their performance in terms of H₂ production is quite similar.     

Regional distribution and pH sensitivity ofAzospirillum associated with wheat roots in Eastern Australia

In a survey ofAzospirillum spp. on the roots and associated soil of wheat grown in eastern Australia, azospirilla were isolated from approximately 40% of samples from areas of soil pH between 5.0 and 6.6. However, azospirilla isolates were rare in soil between pH 4.5 and 5.0 and absent below pH 4.5. Of 25 independent isolates, 17 wereA. brasiliense and eight wereA. lipoferum. No selection forA. brasiliense Nir^– strains by wheat roots was observed. Only one of six endorhizosphere isolates wereA. brasiliense Nir^–, compared with three of nine from unsterilized roots plus associated soil, and three of eight from soil. With a medium buffered with 0.05 M malate and 0.05 M phosphate, it was found that allAzospirillum isolates had a lower minimum pH for growth when supplied with fixed nitrogen than when grown under nitrogen-fixing conditions. Strains isolated from soils had a minimum pH for growth that was less than the pH of the soil from which they were isolated. However, a significant proportion of strains isolated from roots had a minimum pH for growth that was higher than the pH of the associated soil suggesting that the wheat roots provided an ecological niche protecting against soil acidity.     

Horizontal Gene Transfer of PIB-Type ATPases among Bacteria Isolated from Radionuclide- and Metal-Contaminated Subsurface Soils

Aerobic heterotrophs were isolated from subsurface soil samples obtained from the U.S. Department of Energy's (DOE) Field Research Center (FRC) located at Oak Ridge, Tenn. The FRC represents a unique, extreme environment consisting of highly acidic soils with cooccurring heavy metals, radionuclides, and high nitrate concentrations. Four hundred isolates obtained from contaminated soil were assayed for heavy metal resistance, and a smaller subset was assayed for tolerance to uranium. The vast majority of the isolates were gram-positive bacteria and belonged to the high-G+C- and low-G+C-content genera Arthrobacter and Bacillus, respectively. Genomic DNA from a randomly chosen subset of 50 Pb-resistant (Pb^r) isolates was amplified with PCR primers specific for P_IB-type ATPases (i.e., pbrA/cadA/zntA). A total of 10 pbrA/cadA/zntA loci exhibited evidence of acquisition by horizontal gene transfer. A remarkable dissemination of the horizontally acquired P_IB-type ATPases was supported by unusual DNA base compositions and phylogenetic incongruence. Numerous Pb^r P_IB-type ATPase-positive FRC isolates belonging to the genus Arthrobacter tolerated toxic concentrations of soluble U(VI) (UO₂²⁺) at pH 4. These unrelated, yet synergistic, physiological traits observed in Arthrobacter isolates residing in the contaminated FRC subsurface may contribute to the survival of the organisms in such an extreme environment. This study is, to the best of our knowledge, the first study to report broad horizontal transfer of P_IB-type ATPases in contaminated subsurface soils and is among the first studies to report uranium tolerance of aerobic heterotrophs obtained from the acidic subsurface at the DOE FRC.     

Cladosporium sphaerospermum as a new plant growth-promoting endophyte from the roots of Glycine max (L.) Merr.

Endophytic fungi are plant symbionts that produce a variety of beneficial metabolites for plant growth and protection against herbivory and pathogens. Fourteen fungal samples were isolated from the roots of soybean cultivar Daemangkong and screened on waito-c rice for their plant growth-promoting capacity. Twelve of the fungal isolates promoted plant growth, while two inhibited it. The fungal isolate DK-1-1 induced maximum plant growth in both waito-c rice and soybean. The plant growth promotion capacity of DK-1-1 was higher than the wild type Gibberella fujikuroi. Gibberellin (GA) analysis of culture filtrate of DK-1-1 showed the presence of higher amounts of bioactive GA₃, GA₄, and GA₇ (6.62, 2.1 and 1.26 ng/mL, respectively) along with physiologically inactive GA₅, GA₁₅, GA₁₉, and GA₂₄. Phylogenetic analysis of 18S rDNA sequence identified the fungal isolate as a new strain of Cladosporium sphaerospermum. Gibberellin production and plant growth-promoting ability of genus Cladosporium are reported for the first time in the present study. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Host response of rice genotypes to the rice root-knot nematode (Meloidogyne graminicola) under aerobic soil conditions

Aerobic rice is a production system where adapted rice varieties are established via direct seeding in non-puddled, non-flooded, non-saturated fields and grown under conditions similar to upland conditions. On land cultivated continuously with aerobic rice, a yield reduction has been observed. The rice root-knot nematode Meloidogyne graminicola is considered one of the possible causes of these yield reductions. Resistance to and tolerance for M. graminicola are essential traits for aerobic rice cultivars in alleviating this problem. In our study, the host response of nineteen aerobic, seven upland and four lowland rice genotypes which are either being used in the International Rice Research Institute’s aerobic rice breeding programme or already cultivated by farmers in Asia was evaluated under aerobic soil conditions in an outdoor raised-bed experiment. Our study showed a large variation in susceptibility and sensitivity to M. graminicola infection among the rice genotypes examined. Resistance comparable to the resistant reference genotypes included in the experiment (CG14, TOG5674, TOG7235) was not found but in terms of susceptibility, the upland genotype Morobereken may be an interesting less-susceptible genotype. Tolerance was found and in terms of sensitivity, the high yielding aerobic genotype IR78877-208-B-1-2 may be an interesting tolerant genotype. Our study also allowed the identification of rice genotypes that are either highly susceptible or sensitive to M. graminicola infection and of which the cultivation should be discouraged. On average, M. graminicola caused an almost 30% reduction in yield. Excluding the two susceptible and three resistant reference genotypes included in the experiment, most affected was dry-shoot biomass (23.6% reduction) followed by root length, which was more affected than fresh-root weight (19.8 vs. 8%) and grain filling (17.3%), while plant height and the number of spikelets/panicle were less affected (10.2 and 8.1%, respectively). Neither tillering nor the number of panicles/plant were affected.     

Plasmid incidence in bacteria from agricultural and industrial soils

Heavy metal contents of agricultural and industrial soils were determined by atomic absorption spectrophotometry. The analysis of the samples collected from two different locations revealed significantly high levels of Fe, Zn, Cu, Cr and Ni. Certain microbiological parameters (total aerobic heterotrophs, asymbiotic N₂-fixers, total Actinomycetes and fungi) were also monitored from these soils. A total of 70 bacterial isolates from agricultural and industrial soils were examined for plasmid DNA content and resistance to the antibiotics amoxycillin, cloxacillin, chloramphenicol, doxycycline methicillin, nalidixic acid, and tetracycline. Minimum inhibitory concentrations (MICs) of Cu, Cr, Pb, Cd, Hg, Zn, and Ni for each isolate were also determined. Resistance was most frequent to methicillin (48.5%), cloxacillin (45.7%), and nalidixic acid (40%) for all isolates of bacteria. The highest MICs observed were 100 g/ml for mercury, 800 g/ml for Ni and 1600 g/ml for other metals. The incidences of metal resistance and MICs of metals for bacteria from industrial soil were significantly different to those of agricultural soil. On a percentage basis, 91.4% of the total bacterial isolates from industrial soil were found to harbour plasmids whereas 40% of the isolates from agricultural soil contained plasmids.     

Isolation and characterization of fluorescent Pseudomonas associated with the roots of rice and banana grown in Sri Lanka

Bacterial populations in different parts of the rhizosphere of rice and banana in Sri lanka were examined. On rice, the number of aerobic bacteria and the population of fluorescent bacteria were higher in the rhizoplane as compared to the exorhizosphere. However, the opposite was observed with banana. Percentage of fluorescent bacteria was significantly higher on banana (10.8%) than on rice from the wet and dry zones of Sri Lanka (4.3% and 2.7%, respectively). In the endorhizosphere fraction of rice, bacterial populations were very low. Fluorescent bacteria were absent.Based on 33 phenotypical tests, 89 fluorescent isolates were grouped into 5 clusters. The three major clusters covered the isolates belonging to the Pseudomonas fluorescens-putida group, whereas the remaining small clusters contained other UV-fluorescent bacteria. SDS-PAGE of total cell proteins enabled classification of the isolates into one of 12 different protein-polymorphic types. Only a partial correlation was found between the latter classification and the phenotypical one. Cyanogenesis was observed with strains of P. fluorescens only. Isolates P. fluorescens RW9S1 and P. cepacia RW5P1 displayed a potent antagonism against several fungi.     

Characterization of 1-aminocyclopropane-1-carboxylate deaminase producing methylobacteria from phyllosphere of rice and their role in ethylene regulation

The presence of 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity among the phyllosphere methylobacteria of rice was detected and its role in regulating plant ethylene level was assessed. Eighteen methylobacterial isolates from four different cultivars of rice were isolated and screened for ACCD. The 16S rRNA homology of ACCD positive methylobacterial isolate closely related to the species Methylobacterium radiotolerans. The accD gene sequence homology of the isolate was 98% similar to Rhizobium leguminosarum. Foliar spray of ACCD positive methylobacterial isolates enhanced the root and shoot length of rice and tomato seedlings under gnotobiotic condition and lower the ethylene level (60–80%) in the plant species.     

Phosphate solubilization potential and stress tolerance of rhizobacteria from rice soil in Northern Thailand

Plant growth-promoting rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. A total of 216 phosphate-solubilizing bacterial isolates were isolated from different rice rhizospheric soil in Northern Thailand. These isolate were screened in vitro for their plant growth-promoting activities such as solubilization of inorganic phosphate, ammonia (NH₃), catalase and cell wall-degrading enzyme activity. It was found that 100% solubilized inorganic phosphate, 77.77% produced NH₃ and most of the isolates were positive for catalase. In addition, some strains also produced cell wall-degrading enzymes such as protease (7%), chitinase (1%), cellulase (3%) and β-glucanase (3%), as evidenced by phenotypic biochemical test and quantitative assay using spectrophotometry. The isolates could exhibit more than two or three plant growth-promoting (PGP) traits, which may promote plant growth directly or indirectly or synergistically. Part of this study focused on the effect of NaCl, temperature, and pH on a specific the bacterial isolate Acinetobacter CR 1.8. Strain CR 1.8 was able to grow on up to 25% NaCl, between 25 and 55°C, and at pH 5–9. Maximum solubilization of tricalcium phosphate and aluminium phosphate was obtained at neutral pH, and 37°C. Strain CR 1.8 had protease activity but no cellulase, β-glucanase and cellulase activities.     

Endophytic Cephalotheca sulfurea AGH07 reprograms soybean to higher growth

Abstract

Gibberellins (GAs) are well known for plant growth promotion. GAs production by fungi has received little attention, although substantial work has been carried out on other aspects of plant growth-promoting fungi (PGPF). We investigated GAs production and plant growth-promoting capacity of an endophytic fungus isolated from the roots of soil grown soybean plants. The endophytic fungus is reported as GAs producer and as PGPF for the first time in this study. Nine endophytic isolates were collected from the roots of soybean, and culture filtrates (CFs) obtained from their pure cultures were screened on Waito-C, a dwarf rice cultivar, for the presence of GAs. Of these, seven fungal isolates promoted shoot length as compared to control (distilled water), while one inhibited it. Three fungal isolates were selected on the basis of higher shoot elongation as compared to wild type Gibberella fujikuroi, which was used as positive control. The growth-prompting capacity of selected fungal isolates SB5-1, SB3-2, and SB3-3 was bio-assayed on soybean cv. Hwangkeumkong. Fungal isolate SB5-1 provided maximum plant height (31.6 cm), shoot length (21.1 cm), whole plant fresh biomass (2.41 g), shoot fresh biomass (1.99 g), and leaf area (24.37 cm²). The CF of isolate SB5-1 was analyzed for the presence of GAs, and it was found that all physiologically active GAs were present (GA₁, 0.15 ng/ml, GA₃, 1.2 ng/ml, GA₄, 7.37 ng/ml, and GA₇, 3.18 ng/ml) in conjunction with physiologically inactive GA₅, GA₉, GA₁₅, GA₁₉, GA₂₀, and GA₂₄. The fungal isolate SB5-1 was identified as a new strain of Cephalotheca sulfurea through molecular and phylogenetic approaches.     

Viability and metabolic features of bacteria indigenous to a contaminated deep aquifer

The quantitation and characterization of indigenous bacteria of a deep aquifer, located in the southwestern United States and contaminated with halogenated aliphatic compounds, was undertaken. Water samples were obtained aseptically from depths of 45 to 151 m from four sites that ranged from 260 to 1,800 m in distance from the location of contaminant release. Sediment samples were also obtained from the proximal and distal sites for analyses. Results for aerobic and anaerobic colony-forming units were obtained on four agar media that were used to retrieve heterotrophs, oligotrophs, and pseudomonads. Most probable number estimates were obtained from a liquid medium favorable for oligotrophs. Representative isolates were tested against Biolog plates (Biolog, Inc., Hayward, Calif.) for patterns of carbon source utilization. Of 103 Gram-negative (GN) isolates, 48 could not be identified and the others were only tentatively identified via the Biolog database, and none of the 35 Gram-positive (GP) isolates were identifiable. However, the metabolic patterns were subjected to average cluster linkage analyses; the GN and GP bacteria were separable into eight and four groups, respectively. The oligotroph group comprised one-third of the GN and one-half of the GP isolates. The consensus carbon source utilization pattern for each group was determined and will be useful in future characterization of additional aquifer bacterial isolates. Although predominantly aerobic and oligotrophic, the microbial community of this aquifer was highly diverse with discernible viability and metabolic features of the microbiota distinctive to each of the four water and two sediment samples. Correspondence to: C.M. McCarthy.