1. Bipolar Division

2. Soil & Rhizosphere
Oxygen supply limited by mineral particle size, organic matter content and water content.
Plant roots may also add oxygen to deeper soils or anaerobic soils.
Water saturation leads to anaerobic conditions and increased denitrification.
Distribution of microbes depends on organic matter supply and source (humus and root exudates)

3. Oxygen Gradients
Within soil aggregates oxygen decreases toward the interior.
Creates microniches for fermentative and anaerobic respiring bacteria.
Organic matter and availability of alternate electron acceptors (e.g. nitrate, sulfate, carbon dioxide) will partly determine which anaerobic respiring bacteria thrive where.

4. Soil Close-Up
Geosmin = “earthy smell”
= Cyanobacteria
= Actinomycetes

7. Bulk Soil vs Rhizosphere
Bulk soil is that away from the influence of plant roots (i.e. water, oxygen, exudates).
Bulk soil community is subject to greater environmental variability.
Rhizosphere community has greater microbial biomass and activity compared with that in bulk soil.

13. Nitrogen Fixing Actinomycetes
Frankia spp.
Nodulate woody non-leguminous plants, such as Alnus spp (alders).
Association is called actinorhizae.

14. Crown Gall Disease caused by Agrobacterium spp.

15. T-plasmid Function

16. Mycorrhizae Fungi
Hoch et al., 1998
Ectomycorrhizal association between Douglas Fir (Pseudotsuga menziesii) and a boletus-like mushroom (Suillus caerulescens).
Hoch et al., 1999

17. Linking sporocarp to ectomycorrhizae
Kbp
650
492
369
246
123
Internal Transcribed Spacer (ISR) – PCR
Amplifies the region between 18S and 28S rRNA genes in fungi.
RFLP analysis to fingerprint and determine a match (sporocarp to “tip”).
Alu I Hinf I
S T1a T1b S1 T1a T1b