Polyphasic characterization of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (p(HB-co-HV)) metabolizing and denitrifying Acidovorax sp. strains

Decrease of NH4+-N by bacterioplankton accelerated the removal of cyanobacterial blooms in aerated aquatic ecosystem

We used aerated systems to assess the influence of the bacterioplankton community on cyanobacterial blooms in algae/post-bloom of Lake Taihu, China. Bacterioplankton community diversity was evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. Chemical analysis and nitrogen dynamic changes illustrated that NH4+-N was nitrified to NO2--N and NO3--N by bacterioplankton. Finally, NH4+-N was exhausted and NO3--N was denitrified to NO2--N, while the accumulation of NO2--N indicated that bacterioplankton with completely aerobic denitrification ability were lacking in the water samples collected from Lake Taihu. We suggested that adding completely aerobic denitrification bacteria (to denitrify NO2--N to N2) would improve the water quality. PCR-DGGE and sequencing results showed that more than1/3 of the bacterial species were associated with the removal of nitrogen, and Acidovorax temperans was the dominant one. PCR-DGGE, variation of nitrogen, removal efficiencies of chlorophyll-a and canonical correspondence analysis indicated that the bacterioplanktonsignificantly influenced the physiological and biochemical changes of cyanobacteria. Additionally, the unweighted pair-group method with arithmetic means revealed there was no obvious harm to the microecosystem from aeration. The present study demonstrated that bacterioplankton can play crucial roles in aerated ecosystems, which could control the impact of cyanobacterial blooms in eutrophicated fresh water systems.

Characterization of the bacterial community composition in a hypoxic zone induced by Microcystis blooms in Lake Taihu, China

Cyanobacterial blooms have become more frequent as a result of eutrophication in lakes. The accumulation and breakdown of huge cyanobacterial biomasses often cause hypoxia in lakes. However, little is known about microbial diversity in these areas. In this study, we characterized the bacterial community composition of a Microcystis-bloom-induced hypoxic area in Lake Taihu, which is a large, shallow lake, by analysing terminal restriction fragment length polymorphisms of 16S ribosomal RNA genes and clone libraries generated from selected samples. Bacterial samples were collected at different sites within the hypoxic zone at different times during the development of hypoxia. The results showed that the composition of both free-living and particle-attached bacterial communities in the water column varied spatially and temporally and that these variations were largely related to changes in the concentrations of dissolved oxygen and ions in the water column. Sequences affiliated with Clostridium were predominantly found at the onset of hypoxia, whereas members of the LD12 cluster were detected at the posthypoxia stage; Desulfovibrio and Comamonadaceae dominated throughout the hypoxic event. We speculate that these organisms may be associated with the decomposition of Microcystis biomass and the production of volatile organic compounds; however, their specific function in Microcystis-bloom-induced hypoxia warrants further study.

Dynamics of microbial community structure of and enhanced biological phosphorus removal by aerobic granules cultivated on propionate or acetate

Aerobic granules are dense microbial aggregates with the potential to replace floccular sludge for the treatment of wastewaters. In bubble-column sequencing batch reactors, distinct microbial populations dominated propionate- and acetate-cultivated aerobic granules after 50 days of reactor operation when only carbon removal was detected. Propionate granules were dominated by Zoogloea (40%), Acidovorax, and Thiothrix, whereas acetate granules were mainly dominated by Thiothrix (60%). Thereafter, an exponential increase in enhanced biological phosphorus removal (EBPR) activity was observed in the propionate granules, but a linear and erratic increase was detected in the acetate ones. Besides Accumulibacter and Competibacter, other bacterial populations found in both granules were associated with Chloroflexus and Acidovorax. The EBPR activity in the propionate granules was high and stable, whereas EBPR in the acetate granules was erratic throughout the study and suffered from a deterioration period that could be readily reversed by inducing hydrolysis of polyphosphate in presumably saturated Accumulibacter cells. Using a new ppk1 gene-based dual terminal-restriction fragment length polymorphism (T-RFLP) approach revealed that Accumulibacter diversity was highest in the floccular sludge inoculum but that when granules were formed, propionate readily favored the dominance of Accumulibacter type IIA. In contrast, acetate granules exhibited transient shifts between type I and type II before the granules were dominated by Accumulibacter type IIA. However, ppk1 gene sequences from acetate granules clustered separately from those of propionate granules. Our data indicate that the mere presence of Accumulibacter is not enough to have consistently high EBPR but that the type of Accumulibacter determines the robustness of the phosphate removal process.

Submerged filter biofilm formation by nitrate-contaminated groundwater microbiota

Denitrifying biofilms developed in a lab-scale submerged filter by autochthonous bacteria from nitrate-contaminated groundwater were studied. The system was supplied with groundwater (16 mg N-NO(3)(-)/L), from which the oxygen had been eliminated and to which an excess of carbon source had been added. The reactor was incubated in a thermostated chamber at 5°C, 10°C, 20°C and 30°C. Colonization of the support was studied using surface scanning microscopy, and biofilm bacterial composition was studied by PCR/TGGE. Support material was colonized at all the temperatures assayed, although this parameter affected the growth of the biofilm, which developed most at temperatures over 20°C. The composition of bacterial communities varied according to the temperature. Community profiles of the biofilm formed at 5°C and 10°C clustered away from those of the biofilm formed at 20°C and 30°C. 16S rDNA sequences reveled that the biofilm was mainly composed of psychrotolerant species typically inhabiting freshwaters, and we obtained sequencing bands that were affiliated to denitrifying and non-denitrifying heterotrophic species. The extent of colonization was low when compared to previously inoculated systems, and the capacity for nitrate elimination was also low.

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.

Identity and potential functions of heterotrophic bacterial isolates from a continuous-upflow fixed-bed reactor for denitrification of drinking water with bacterial polyester as source of carbon and electron donor

A collection of 186 heterotrophic bacteria, isolated directly from a continuous-upflow fixed-bed reactor for the denitrification of drinking water, in which poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) granules acted as biofilm carrier, carbon source and electron donor, was studied with regard to taxonomic affiliation and degradation and denitrification characteristics. Two granule samples were taken from a fully operating reactor for enumeration and isolation of heterotrophic bacteria. One sample was drawn from the lower part of the reactor, near the oxic zone, and the other sample from the upper, anoxic part of the fixed bed. Dominant colonies were isolated and the cultures were identified using fatty acid analysis and 16S rDNA sequencing. Their ability to degrade the polymer and 3-hydroxybutyrate and to denitrify in pure culture was assessed. The results show that high numbers of heterotrophic bacteria were present in the biofilms on the polymer granules, with marked differences in taxonomic composition and potential functions between the lower and upper part of the fixed bed. The majority of the isolates were Gram negative bacteria, and most of them were able to reduce nitrate to nitrite or to denitrify, and to utilize 3-hydroxybutyrate as sole source of carbon. Only two groups, one identified as Acidovorax facilis and the other phylogenetically related to Brevundimonas intermedia, could combine denitrification and utilization of poly(3-hydroxybutyrate) (PHB), and were found only in the upper sample. The other groups occurred either in the lower or upper part, or in both samples. They were assigned to Brevundimonas, Pseudomonas, Agrobacterium, Achromobacter, or Phyllobacterium, or were phylogenetically related to Afipia or Stenotrophomonas.