, Volume 8, Issue 6, pp 421-427

Microbial flora of some soils of Mawson Base and the Vestfold Hills, Antarctica

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A microbiological survey of 40 soils from contaminated and pristine localities of Mawson Base or the Vestfold Hills (Davis Base) is described. High microbial populations (from 106 to in excess of 109 cells g-1 dry soil) were associated with soil contaminated by man or animals, soil from beneath a moss bed, or soil from beneath translucent quartz pebbles and containing green algae. Lower microbial populations (generally between 104–106 cells g-1 soil) were associated with pristine soils lacking an identifiable primary producer. No correlation was evident between population density and soil particle size, moisture content, pH or salinity as determined by the electrical conductivity (E.C.) of soil suspensions, although relationships were evident between the components of the microflora and E.C. Microbial groups associated with low E.C. were chitinolytic bacteria, fungi and green algae; favoured by high E.C. were halotolerant bacteria. The microflora of uncontaminated soils appeared to be dominated by Gram-negative aerobic rods (68% of the total flora) with Moraxella, Acinetobacter and Pseudomonas being the most frequently isolated genera. The remaining microflora comprised Grampositive pleomorphic bacteria (mainly coryneforms), 13%; filamentous Gram-negative aerobic rods (morphologically akin to Bacillus species), 12%; and yeasts, 7%. Streptomyces was identified among the dominant microflora of only one soil. Nitrogen-fixing bacteria were never isolated, although their presence was indicated in 40% of the soils tested by acetylene-reduction assay. Anaerobes were not detected in any soil using dilutionplate techniques, but were occasionally detected by enrichment in semi-solid media. All of 242 isolates obtained at 10° incubation were able to grow at 15°, 3.3% failed to grow at 18° and a further 9.5% failed to grow at 25°. Of 304 isolates obtained on one-tenth strength Trypticase-Soy agar (0.05% nutrient concentration), 10% failed to grow on the full-strength medium. Soils from the vicinity of Mawson or Davis bases contained a variety of fungi (Cladosporium, Chrysosporium, Acremonium, Phoma, Aureobasidium and Trichoderma species being isolated) in contrast to pristine soils, from which only Verticillium was occasionally isolated.