Succession of Bacterial Communities during Early Plant Development: Transition from Seed to Root and Effect of Compost Amendment

Abstract

Compost amendments to soils and potting mixes are routinely applied to improve soil fertility and plant growth and health. These amendments, which contain high levels of organic matter and microbial cells, can influence microbial communities associated with plants grown in such soils. The purpose of this study was to follow the bacterial community compositions of seed and subsequent root surfaces in the presence and absence of compost in the potting mix. The bacterial community compositions of potting mixes, seed, and root surfaces sampled at three stages of plant growth were analyzed via general and newly developed Bacteroidetes-specific, PCR-denaturing gradient gel electrophoresis methodologies. These analyses revealed that seed surfaces were colonized primarily by populations detected in the initial potting mixes, many of which were not detected in subsequent root analyses. The most persistent bacterial populations detected in this study belonged to the genus Chryseobacterium (Bacteroidetes) and the family Oxalobacteraceae (Betaproteobacteria). The patterns of colonization by populations within these taxa differed significantly and may reflect differences in the physiology of these organisms. Overall, analyses of bacterial community composition revealed a surprising prevalence and diversity of Bacteroidetes in all treatments.

Contrasting patterns of seed and root colonization by bacteria from the genus Chryseobacterium and from the family Oxalobacteraceae

“…With increasing proximity to the root, we observed a strong rhizosphere effect, and that the plant influence on bacteria from the genus Streptomyces predominated over soil and compost effects (Inbar et al, 2005). In a more general analysis of bacterial communities associated with plant seeds and roots, we observed that while seed surfaces were largely colonized by dominant potting mix populations, root microbial communities differed significantly from the source potting mix communities (Green et al, 2006). However, despite a general divergence between the community composition of seed and root bacteria, two distinct taxonomic groups were consistently detected in seed and root communities.…”

“…Plant growth sampling and DNA extraction Cucumber seeds (Cucumis sativus L. 'straight eight') were sown in three peat-based potting mixes amended with composts, as previously described (Green et al, 2006). The two composts employed were sawdust-amended ('sawdust compost') and straw-amended ('straw compost') cow manure composts, as previously described (Changa et al, 2003;Green et al, 2004).…”

“…Both are common to soil environments, and are aerobic, heterotrophic organisms (Kwok et al, 1987;Spiegel et al, 1991;Bowman et al, 1993;Bernardet et al, 2005). However, isolated members of the genus Telluria are flagellated and have chitinolytic, proteolytic and collagenolytic activity (Spiegel et al, 1991;Bowman et al, 1993), while Chryseobacterium are non-motile, heterotrophic organisms, frequently found in composted materials and other organic-rich environments (Kwok et al, 1987;Bernardet et al, 2005;Green et al, 2004Green et al, , 2006. In this study, we investigated these taxa more closely to characterize the interaction of the rhizosphere effect and the influence of compost amendment as it varied between these seed-and root-colonizing microorganisms.…”

“…Compost amendment to soil is a common agricultural technique and, by introducing large amounts of organic matter as well as high numbers and a large diversity of microorganisms, it can substantially modify soil chemistry and structure and can significantly influence the composition of plant-associated microbial communities (Dick and McCoy, 1993;Beffa et al, 1996;Tiquia et al, 2002;Ryckeboer et al, 2003;Inbar et al, 2005;Green et al, 2006). Soil organic matter can be a significant source of carbon for some rhizosphere organisms (Toal et al, 2000), and Boehm et al (1997) have suggested that the addition of compost to soil can support microorganisms that are not sustained by root exudates.…”

“…However, despite a general divergence between the community composition of seed and root bacteria, two distinct taxonomic groups were consistently detected in seed and root communities. These taxa included a clade of organisms closely related to the genus Telluria, within the family Oxalobacteraceae (Betaproteobacteria) and bacteria from the genus Chryseobacterium (Bacteroidetes) (Green et al, 2006). Both are common to soil environments, and are aerobic, heterotrophic organisms (Kwok et al, 1987;Spiegel et al, 1991;Bowman et al, 1993;Bernardet et al, 2005).…”