The Microflora of Peat‐podzol Transitions

Summary Bacteria made up an average of 90 per cent of the microbial populations of twenty‐four soil samples, mainly of the A 0 H horizon, from four peat‐podzol transitions. Bacillus spp., which averaged 67 per cent of these bacteria, were usually the predominant group. Gram‐negative non‐spore‐forming organisms (15 per cent), Streptomyces (8 per cent), and Gram‐positive cocci (5 per cent) occurred irregularly and Arthrobacter and Nocardia strains rarely. A large proportion of the strains utilized glucose and malate, and a smaller proportion starch, citrate, and protein. A few strains liquefied pectin but none decomposed cellulose or xylan. In eight populations examined, 80 per cent of the bacteria required yeast extract for growth. Fungi usually formed only a small proportion of the populations. All the species, except Penicillium nigricans and Trichoderma viride , were isolated from only one transition. Yeasts occurred irregularly, usually in small numbers. Whilst no microbial group responded to the addition of glucose, nitrate, and phosphate to two soil samples, bacterial numbers increased after the addition of peptone and yeast extract.