Interaction between poly-3-hydroxybutyrate-co-3-hydroxyvalerate and a denitrifying Pseudomonas strain

Application of polyhydroxyalkanoates for denitrification in water and wastewater treatment

Application of polyhydroxyalkanoates (PHAs) and related biodegradable polymers has gained momentum in various areas of biotechnology. A promising application that started appearing in the past decade is the use of PHAs as the solid substrate for denitrification of water and wastewater. This type of denitrification, termed here "solid-phase denitrification", has several advantages over the conventional system supplemented with liquid organic substrate. PHAs serve not only as constant sources of reducing power for denitrification but also as solid matrices favorable for development of microbial films. In addition, in contrast to conventional processes, the use of PHAs has no potential risk of release of dissolved organic carbon with the resultant deterioration of effluent water quality. If the production cost of PHAs can be brought down, its application to the denitrification process will become economically more promising. A number of PHA-degrading denitrifying bacteria have been isolated and characterized from activated sludge and continuous flow-bed reactors for denitrification with PHAs. Most of these isolates have been assigned phylogenetically to members of beta-Proteobacteria, especially those of the family Comamonadaceae. The metabolic and regulatory relationships between PHA degradation and denitrification, and the interactive relationship between PHA-degrading cells and the solid surface structure are important subjects awaiting future studies, which would provide a new insight into our comprehensive understanding of the solid-phase denitrification process.

Diaphorobacter nitroreducens gen nov, sp nov, a poly(3-hydroxybutyrate)-degrading denitrifying bacterium isolated from activated sludge

Three denitrifying strains of bacteria capable of degrading poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were isolated from activated sludge and characterized. All of the isolates had almost identical phenotypic characteristics. They were motile gram-negative rods with single polar flagella and grew well with simple organic compounds, as well as with PHB and PHBV, as carbon and energy sources under both aerobic and anaerobic denitrifying conditions. However, none of the sugars tested supported their growth. The cellular fatty acid profiles showed the presence of C16:1omega7cis and C16:0 as the major components and of 3-OH-C10:0 as the sole component of hydroxy fatty acids. Ubiquinone-8 was detected as the major respiratory quinone. A 16S rDNA sequence-based phylogenetic analysis showed that all the isolates belonged to the family Comamonadaceae, a major group of beta-Proteobacteria, but formed no monophyletic cluster with any previously known species of this family. The closest relative to our strains was an unidentified bacterium strain LW1 (=DSM 13225) (99.9% similarity), reported previously as a 1-chloro-4-nitrobenzene degrading bacterium. DNA-DNA hybridization levels among the new isolates were more than 60%, whereas those between our isolates and strain DSM 13225 were less than 50%. The G+C content of genomic DNA of the new strains was 64 to 65 mol%. Based on these results, we concluded that the PHBV-degrading denitrifying isolates should be classified as a new genus and a new species, for which we propose the name Diaphorobacter nitroreducens. The type strain is strain NA10B (=JCM 11421=CIP 107294). We also propose to classify strain DSM 13225 as a genospecies of Diaphorobacter.

Members of the family Comamonadaceae as primary poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-degrading denitrifiers in activated sludge as revealed by a polyphasic approach

The distribution and phylogenetic affiliations of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)-degrading denitrifying bacteria in activated sludge were studied by a polyphasic approach including culture-independent biomarker and molecular analyses as well as cultivation methods. A total of 23 strains of PHBV-degrading denitrifiers were isolated from activated sludges from different sewage treatment plants. 16S ribosomal DNA (rDNA) sequence comparisons showed that 20 of the isolates were identified as members of the family Comamonadaceae, a major group of beta-Proteobacteria. When the sludges from different plants were acclimated with PHBV under denitrifying conditions in laboratory scale reactors, the nitrate removal rate increased linearly during the first 4 weeks and reached 20 mg NO(3)(-)-N h(-1) g of dry sludge(-1) at the steady state. The bacterial-community change in the laboratory scale sludges during the acclimation was monitored by rRNA-targeted fluorescence in situ hybridization and quinone profiling. Both approaches showed that the population of beta-Proteobacteria in the laboratory sludges increased sharply during acclimation regardless of their origins. 16S rDNA clone libraries were constructed from two different acclimated sludges, and a total of 37 clones from the libraries were phylogenetically analyzed. Most of the 16S rDNA clones were grouped with members of the family Comamonadaceae. The results of our polyphasic approach indicate that beta-Proteobacteria, especially members of the family Comamonadaceae, are primary PHBV-degrading denitrifiers in activated sludge. Our data provide useful information for the development of a new nitrogen removal system with solid biopolymer as an electron donor.

Isolation and characterization of a new poly(3-hydroxybutyrate)-degrading, denitrifying bacterium from activated sludge

A new denitrifying chemoorganotrophic bacterium capable of aerobic and anaerobic degradation of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) was isolated from activated sludge. A phylogenetic analysis based on 16S rDNA sequences indicated that the new isolate is a member of the beta subclass of the Proteobacteria and represents a distinct line of descent within the family Comamonadaceae. During denitrifying growth with 3-hydroxybutyrate, PHB, or PHBV as the sole carbon source, the isolate reduced nitrate to N2 without appreciable accumulation of nitrite and nitrous oxide as intermediate products. Kinetic analyses of the denitrification with different grades of PHBV indicated that approximately 0.7 g of PHBV was required to reduce 1 g of NO3-. A high denitrification rate (19 mg N-NO3- removed h(-1) x g(-1) dry wt of cells) was found with PHBV as the electron donor.