title: Floc Formation by Azospirillum lipoferum Grown on Poly-beta-Hydroxybutyrate.
abstract: Azospirillum lipoferum RG6xx was grown under conditions similar to those resulting in encystment of Azotobacter spp. A. lipoferum produced cells of uniform shape when grown on nitrogen-free beta-hydroxybutyrate agar. Cells accumulated poly-beta-hydroxybutyrate and often grew as chains or filaments that eventually lost motility and formed capsules. Within 1 week, vegetative A. lipoferum inocula were converted into microflocs arising from filaments or chains. Cells within microflocs were pleomorphic, contained much poly-beta-hydroxybutyrate, and were encapsulated. Some cells had a cystlike morphology. Up to 57% of the dry weight of encapsulated flocs was poly-beta-hydroxybutyrate, whereas vegetative cells grown in broth with combined nitrogen had only 3% of their dry weight as poly-beta-hydroxybutyrate. Neither encapsulated cells in flocs nor nonencapsulated vegetative cells were significantly desiccation resistant. Under starvation conditions (9 days) only 25% of encapsulated cells remained viable, whereas vegetative cells multiplied severalfold. In short-term germination experiments with encapsulated flocs, nitrate, ammonium, and soil extract promoted formation of motile vegetative cells. Most cells in treatments lacking combined nitrogen eventually depleted their visible poly-beta-hydroxybutyrate reserves without germinating. The remaining cells retained the reserve polymer and underwent size reduction.
authors.affiliation: Department of Agronomy, Department of Soil Science, and Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611.
authors.forename: B H
authors.initials: BH
authors.lastname: Bleakley
authors.forename: M H
authors.initials: MH
authors.lastname: Gaskins
authors.forename: D H
authors.initials: DH
authors.lastname: Hubbell
authors.forename: S G
authors.initials: SG
authors.lastname: Zam