MCB 150 Plant as Habitat

• Plant microbiome


  Varied assembly of microorganisms residing both externally and internally within the host plant

  
• Components of the plant microbiome


  • Rhizosphere
  • Endosphere
  • Phyllosphere

  
• Rhizosphere


  1. 10 mm of soil surrounding plant roots, influenced by root exudates, mucilage, and plant debris
• Organisms in the rhizosphere


  • Bacteria
  • Fungi
  • Nematodes
  • Archaea

  
• Rhizosphere


  • Hosts a diverse community, with certain bacterial taxa dominating
  • Differences from bulk soil aren't always significant

  
• Mycorrhizal fungi


  Prevalent in the rhizosphere, form vital associations with numerous plant species, play crucial roles in nutrient cycling
• Zones of the rhizosphere


  • Endorhizosphere
  • Rhizoplane
  • Ectorhizosphere
• Rhizosphere


  Differs from bulk soil due to higher microbial activity and root exudate levels

  
• Phyllosphere


  Encompasses the aerial parts of plants, relatively nutrient-poor compared to the rhizosphere and endosphere, experiences dynamic environmental fluctuations
• Dominant microbes in the phyllosphere


  • Proteobacteria
  • Bacteroidetes
  • Actinobacteria

  
• Phyllosphere communities show low resemblance to those in the open air, indicating a need for finely tuned metabolic adaptations for survival in this environment
• Endosphere


  Microorganisms that infiltrate and inhabit the internal tissues of plants

  
• Dominant microbes in the endosphere


  • Arbuscular mycorrhizal (AM) fungi
  • Other endophytic fungi
  • Bacteria
  • Archaea

  
• Endospheric microbiome


  • Highly specialized, often distinct from those in the surrounding soil
  • Generally lower diversity than external microbial communities

  
• The identity and diversity of endophytic microbiomes can vary between above-ground and below-ground plant tissues

  
• Soil


  Challenging environment for roots, microorganisms, and soil fauna due to physical constraints and variable resource availability
• Soil factors influencing root microbiome


  • Soil type
  • pH
  • Nutrient levels
• Soil pH plays a significant role in shaping microbiome composition, but the exact mechanisms remain unclear

  
• Soil properties like temperature and contaminants also impact microbiome composition
• Cultivation practices


  Changes in land use and cultivation practices are major contributors to declines in biodiversity
• Effects of cultivation practices on soil microbiome


  • Can be positive, negative, or neutral
  • Intensity of land use shapes bacterial community patterns
  • Continuous cultivation leads to changes in soil properties
• Climate


  Plays a crucial role in shaping both plant and soil microbiome compositions
• Climatic factors influencing microbiome


  • Rainfall
  • Temperature
• Precipitation emerges as a significant driver of soil microbial community composition, with both fungi and bacteria biomass increasing with higher mean annual precipitation
• Examples of microorganisms in the phyllosphere


  • Yeast species (Cryptococcus, Sporobolomyces, Rhodotorula)
  • Molds (Mucor, Alternaria, Penicillium, Acremonium, Aspergillus)
  • Bacteria (Proteobacteria, Firmicutes, Bacteroides, Actinobacteria)

  
• Endophytes


  Microorganisms that infiltrate and inhabit the internal tissues of plants

  
• Endophytic microorganisms


  • Mainly form mutualistic relationships with their host
  • Provide a stable environment unaffected by changing environmental circumstances
• Fungal endophytes


  Produce bioactive metabolites, primarily terpenoids and alkaloids, that are antimicrobial in nature, improving the quality of their host's growth
• Examples of endophyte-conferred benefits


  • Stress tolerance
  • Herbivore deterrence
  • Improved defense mechanisms against pathogenic microorganisms
• Bacterial groups more prevalent in the rhizosphere


  • Bacteroidetes
  • Proteobacteria
• Bacterial genera more abundant in the bulk soil


  • Haliangium
  • Pseudolabrys
  • Acidibacter
  • Nitrosospira
  • Gaiella
  • Blastococcus
  • Nocardioides
  • Conexibacter
• Mycorrhizae


  Mutualistic relationships between fungal and plant species wherein nutrients flow in both directions

  
• Through comparison of 16s rRNA genes (culture-independent approach), the bacterial groups Bacteroidetes and Proteobacteria were more prevalent in the rhizosphere compared to the overall samples
• Certain genera within the Proteobacteria phylum, including Haliangium, Pseudolabrys, Acidibacter, and Nitrosospira, were more abundant in the bulk soil

  
• Actinobacteria were also more abundant in the rhizosphere of most plants, but certain genera like Gaiella, Blastococcus, Nocardioides, and Conexibacter were primarily found in the bulk soil

  
• Mycorrhizae


  Mutualistic relationships between fungal and plant species wherein nutrients flow in both directions (plant to fungi, vice versa)

  
• Mycorrhizae


  • Fungi involved can't break down complex sugars, which are the prevalent food source in soil
  • Plants benefit from this relationship through access to phosphorus and nitrogen, communicated by the fungi
  • Fungi get access to simple sugars like glucose from the plant
  • Fungi usually struggle to survive solely by breaking down dead organic matter
• Types of mycorrhizae


  • Endomycorrhizae
  • Ectomycorrhizae
• Ectomycorrhizae


  • Have a shallow penetration of the root cellular structure
  • Form extensive sheath structures called "fungal mantle" which extends the reach of plants to obtain nutrients
  • Nutrient exchange occurs in the "Hartig net", the junction between the fungi and the roots
  • Primarily inhabit the roots of forest trees, particularly conifers like pines, along with beeches and oaks
  • Thrive predominantly in boreal and temperate forest environments
• Ectomycorrhizae


  • Suillus granulatus (associated with pine trees)