Determinants of A cidobacteria activity inferred from the relative abundances of 16 S rRNA transcripts in G erman grassland and forest soils

Abstract

Summary 16 S rRNA genes and transcripts of A cidobacteria were investigated in 57 grassland and forest soils of three different geographic regions. A cidobacteria contributed 9–31% of bacterial 16 S rRNA genes whereas the relative abundances of the respective transcripts were 4–16%. The specific cellular 16 S rRNA content (determined as molar ratio of rRNA : rRNA genes) ranged between 3 and 80, indicating a low in situ growth rate. Correlations with flagellate numbers, vascular plant diversity and soil respiration suggest that biotic interactions are important determinants of A cidobacteria 16 S rRNA transcript abundances in soils. While the phylogenetic composition of A cidobacteria differed significantly between grassland and forest soils, high throughput denaturing gradient gel electrophoresis and terminal restriction fragment length polymorphism fingerprinting detected 16 S rRNA transcripts of most phylotypes in situ . Partial least squares regression suggested that chemical soil conditions such as pH , total nitrogen, C : N ratio, ammonia concentrations and total phosphorus affect the composition of this active fraction of A cidobacteria . Transcript abundance for individual A cidobacteria phylotypes was found to correlate with particular physicochemical ( pH , temperature, nitrogen or phosphorus) and, most notably, biological parameters (respiration rates, abundances of ciliates or amoebae, vascular plant diversity), providing culture‐independent evidence for a distinct niche specialization of different A cidobacteria even from the same subdivision.

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