Differences in Microbial Activity and Microbial Populations of Peat Associated with Suppression of Damping-Off Disease Caused by Pythium sylvaticum

Abstract

The microbiological characteristics associated with disease-suppressive peats are unclear. We used a bioassay for Pythium sylvaticum-induced damping-off of cress seedlings to identify conducive and suppressive peats. Microbial activity in unconditioned peats was negatively correlated with the counts of P. sylvaticum at the end of the bioassay. Denaturing gradient gel electrophoresis (DGGE) profiling and clone library analyses of small-subunit rRNA gene sequences from two suppressive and two conducive peats differed in the bacterial profiles generated and the diversity of sequence populations. There were also significant differences between bacterial sequence populations from suppressive and conducive peats. The frequencies of a number of microbial groups, including the RhizobiumAgrobacterium group (specifically sequences similar to those for the genera Ochrobactrum and Zoogloea) and the Acidobacteria, increased specifically in the suppressive peats, although no single bacterial group was associated with disease suppression. Fungal DGGE profiles varied little over the course of the bioassay; however, two bands associated specifically with suppressive samples were detected. Sequences from these bands corresponded to Basidiomycete yeast genera. Although the DGGE profiles were similar, fungal sequence diversity also increased during the bioassay. Sequences highly similar to those of Cryptococcus increased in relative abundance during the bioassay, particularly in the suppressive samples. This study highlights the importance of using complementary approaches to molecular profiling of complex populations and provides the first report that basidiomycetous yeasts may be associated with the suppression of Pythium-induced diseases in peats.

Effect of decomposition on physical properties of fibrous peat

“…However, the mean microorganism counts recorded for the peat in Table 3 are consistent with reported values for peats of ~2•6 × 10 5 CFU/g (Hunter et al, 2006) and within the range 2•2 × 10 5 to 1•5 × 10 6 CFU/g (Pichan and O'Kelly, 2013). Average values listed for the different specimen sets in Table 3 are used later in the paper as reference values for evaluating the decomposition rate.…”

“…Some of these microorganisms are expected to be key decomposers with cellulolytic potential (e.g., Firmicutes, Bacteroidetes, Acidobacteria and Cytophaga) as well as fungi capable of degrading celluloses in peat (Hunter et al, 2006;Pankratov et al, 2011). However, it was not possible to determine the actual types (species) of microorganisms in the peat using the technique employed and it was considered beyond the scope of this study.…”

“…In many soil deposits, estimated total microbial populations are of the order of 10 9 -10 12 /kg soil at near the ground surface (Mitchell and Santamarina, 2005). However, the microbial population and activity in peat material have hardly been explored and are less well understood (Hingley, 1993;Hunter et al, 2006;Pichan and O'Kelly, 2013), although it is known that microbial populations possessing versatile cellulolytic and hydrolytic capabilities for Environmental Geotechnics Volume 1 Issue EG1 degrading cellulose, soluble phenolics, pectin, starch, chitin and other biopolymers are present in peat (Pankratov et al, 2011).…”

Stimulated decomposition in peat for engineering applications

“…6 3 10 5 CFU/g dry peat (Hunter et al, 2006), where CFU is colony-forming unit, a measure of the microorganism population present. Cellulose substrates may be degraded by Acidobacteria or Cytophaga-like bacteria, which possess cellulolytic potential and are commonly found in peat (Pankratov et al, 2011).…”

“…Fungi are also active in the acrotelm, with mean fungal counts of ,3 . 7 3 10 6 CFU/g dry peat (Hunter et al, 2006), although their growth rate declines with depth on account of increasingly anaerobic and saturated conditions. Fungi possess versatile hydrolytic capabilities and are capable of degrading cellulose, soluble phenolics, pectin, starch, chitin and other biopolymers (Pankratov et al, 2011).…”