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Floc Formation by Azospirillum lipoferum Grown on Poly-beta-Hydroxybutyrate.
B H Bleakley1, M H Gaskins, D H Hubbell
1Department of Agronomy, Department of Soil Science, and Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611.
Applied and Environmental Microbiology
|December 1, 1988
Summary
Azospirillum lipoferum RG6xx forms encapsulated microflocs with high poly-beta-hydroxybutyrate (PHB) content under nitrogen-free conditions. These microflocs do not enhance desiccation resistance but can germinate into motile cells when nutrients are available.
Area of Science:
- Microbiology
- Bacteriology
- Biochemistry
Background:
- Azospirillum lipoferum is a nitrogen-fixing bacterium.
- Encystment is a survival strategy observed in some bacteria, like Azotobacter spp.
- Poly-beta-hydroxybutyrate (PHB) is a carbon and energy storage polymer in bacteria.
Purpose of the Study:
- To investigate the morphological changes and poly-beta-hydroxybutyrate accumulation in Azospirillum lipoferum RG6xx under conditions mimicking Azotobacter spp. encystment.
- To assess the viability and desiccation resistance of encapsulated Azospirillum lipoferum cells.
Main Methods:
- Culturing Azospirillum lipoferum RG6xx on nitrogen-free beta-hydroxybutyrate agar.
- Microscopic observation of cell morphology, including filamentation, microfloc formation, and encapsulation.
- Quantification of poly-beta-hydroxybutyrate (PHB) content in vegetative and encapsulated cells.
- Assessing cell viability and desiccation resistance under starvation and germination conditions.
Main Results:
- Azospirillum lipoferum RG6xx formed uniform cells, then filaments and chains accumulating PHB, eventually forming encapsulated microflocs.
- Encapsulated cells within microflocs had significantly higher PHB content (up to 57% dry weight) compared to vegetative cells (3%).
- Encapsulated cells showed limited desiccation resistance and viability under starvation, with only 25% survival after 9 days, while vegetative cells multiplied.
Conclusions:
- Azospirillum lipoferum RG6xx undergoes morphological changes and accumulates PHB, forming encapsulated structures under specific nutrient-limited conditions.
- The observed microflocs do not confer significant desiccation resistance to Azospirillum lipoferum.
- Germination of encapsulated cells into motile vegetative cells is promoted by the presence of nitrate, ammonium, or soil extract, indicating a potential role in nutrient scavenging and survival.