Improved productivity of poly (3-hydroxybutyrate) (PHB) in thermophilic Chelatococcus daeguensis TAD1 using glycerol as the growth substrate in a fed-batch culture.

A particularly successful polyhydroxyalkanoate (PHA) in industrial applications is poly (3-hydroxybutyrate) (PHB). However, one of the major obstacles for wider application of PHB is the cost of its production and purification. Therefore, it is desirable to discover a method for producing PHB in large quantities at a competitive price. Glycerol is a cheap and widely used carbon source that can be applied in PHB production process. There are numerous advantages to operating fermentation at elevated temperatures; only several thermophilic bacteria are able to accumulate PHB when glycerol is the growth substrate. Here, we report on the possibility of increasing PHB production at low cost using thermophilic Chelatococcus daeguensis TAD1 when glycerol is the growth substrate in a fed-batch culture. We found that (1) excess glycerol inhibited PHB accumulation and (2) organic nitrogen sources, such as tryptone and yeast extract, promoted the growth of C. daeguensis TAD1. In the batch fermentation experiments, we found that using glycerol at low concentrations as the sole carbon source, along with the addition of mixed nitrate (NH4Cl, tryptone, and yeast extract), stimulated PHB accumulation in C. daeguensis TAD1. The results showed that the PHB productivity decreased in the following order: two-stage fed-batch fermentation > fed-batch fermentation > batch fermentation. In optimized culture conditions, a PHB amount of 17.4 g l(-1) was obtained using a two-stage feeding regimen, leading to a productivity rate of 0.434 g l(-1) h(-1), which is the highest productivity rate reported for PHB to date. This high PHB biosynthetic productivity could decrease the total production cost, allowing for further development of industrial applications of PHB.

Comparative study on the production of poly(3-hydroxybutyrate) by thermophilic Chelatococcus daeguensis TAD1: a good candidate for large-scale production.

In spite of numerous advantages on operating fermentation at elevated temperatures, very few thermophilic bacteria with polyhydroxyalkanoates (PHAs)-accumulating ability have yet been found in contrast to the tremendous mesophiles with the same ability. In this study, a thermophilic poly(3-hydroxybutyrate) (PHB)-accumulating bacteria (Chelatococcus daeguensis TAD1), isolated from the biofilm of a biotrickling filter used for NOx removal, was extensively investigated and compared to other PHB-accumulating bacteria. The results demonstrate that C. daeguensis TAD1 is a growth-associated PHB-accumulating bacterium without obvious nutrient limitation, which was capable of accumulating PHB up to 83.6 % of cell dry weight (CDW, w/w) within just 24 h at 45 °C from glucose. Surprisingly, the PHB production of C. daeguensis TAD1 exhibited strong tolerance to high heat stress as well as nitrogen loads compared to that of other PHB-accumulating bacterium, while the optimal PHB amount (3.44 ± 0.3 g l(-1)) occurred at 50 °C and C/N = 30 (molar) with glucose as the sole carbon source. In addition, C. daeguensis TAD1 could effectively utilize various cheap substrates (starch or glycerol) for PHB production without pre-hydrolyzed, particularly the glycerol, exhibiting the highest product yield (Y P/S, 0.26 g PHB per gram substrate used) as well as PHB content (80.4 % of CDW, w/w) compared to other carbon sources. Consequently, C. daeguensis TAD1 is a viable candidate for large-scale production of PHB via utilizing starch or glycerol as the raw materials.

Isolation and characterization of a thermophilic Bacillus shackletonii K5 from a biotrickling filter for the production of polyhydroxybutyrate.

Polyhydroxyalkanoates (PHAs) are aliphatic polyesters accumulated intracellularly by both Gram-negative and Gram-positive bacteria. However, compared to the PHAs of Gram-negative bacteria, few endotoxins (lipopolysaccharides, LPS), which would be co-purified with PHAs and cause immunogenic reactions, are found in the PHAs produced by Gram-positive bacteria. A thermophilic Gram-positive bacterium K5, which exhibited good growth and polyhydroxybutyrate (PHB)-accumulating ability, has been isolated and characterized from a biotrickling filter designed for the removal of NOx from flue gas in a coal-fired power plant in China. Based on the biochemical characterization and 16S rRNA gene sequence (Genbank accession no. JX437933), the strain K5 has been identified as Bacillus shackletonii, which has rarely been reported in the literature, and this report is the first time that B. shackletonii has been found to accumulate PHB. The strain K5 was able to utilize glucose as carbon source to synthesize PHB at a broad range of temperatures (from 35 to 50°C), and the ideal temperature was 45°C. The strain K5 could effectively yield PHB of up to 69.9% of its cell dry weight (CDW) (2.28 g/L) in flask experiments employing glucose as carbon source at 45°C, followed by 56.8% and 52.3% of its CDW when using sodium succinate and glycerol as carbon source, respectively. For batch cultivation, the strain K5 was able to produce PHB of up to 72.6% of its cell dry weight (9.76 g/L) employing glucose as carbon source at 45°C and pH7.0.

Nitrogen removal by Chelatococcus daeguensis TAD1 and its denitrification gene identification.

Chelatococcus daeguensis TAD1 was demonstrated to be an aerobic denitrifier. It can utilize not only nitrate and nitrite but also ammonium at high temperature (about 50 °C). The strain had the capability to remove 122.7 and 71.7 mg L−1 NH4+-N by 18 h at 50 and 30 °C, respectively. Triplicate heterotrophic nitrification experiments showed that 32.3 % of removed NH4+-N was completely converted to nitrogen gas by 18 h at 50 °C. The denitrification genes involved in C. daeguensis TAD1 were identified and sequenced. It was found that the genes responsible for denitrification in TAD1 were napA, nirK, cnorB, and nosZ. Taken together, TAD1 can be an effective candidate for simultaneous nitrification and denitrification at high temperature.

Submerged arc furnace process superior to the Waelz process in reducing PCDD/F emission during thermal treatment of electric arc furnace dust.

Besides the Waelz process, the submerged arc furnace (SAF) process has also been extensively used to retain metals from ashes and scraps in the metallurgical industry. However, very little is known about the formation and depletion of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from this thermal process. In this study, an electric arc furnace (EAF) dust treatment plant adopting the SAF process was investigated and compared to the plant adopting the Waelz process. The predominant contributor of PCDD/F I-TEQ input was the EAF dusts, accounting for 98.4% of the total. The PCDD/F contents in the generated fly ashes of the SAF were extremely low, as almost all the organic compounds for PCDD/F formation were decomposed by the high operating temperatures (1500-1700 °C) of the SAF. Therefore, the PCDD/F emission factor of the SAF process (46.9 µg I-TEQ/tonne-EAF dust) was significantly lower than that of the Waelz process (840-1120 µg I-TEQ/tonne-EAF dust). Its PCDD/F output/input ratios (0.23 and 0.50 based on mass and toxicity) were also lower than those of the Waelz process plant (0.62 and 1.19). Therefore, the SAF process is superior to the Waelz process in reducing the potential of PCDD/F formation.

Microbial removal of NOX at high temperature by a novel aerobic strain Chelatococcus daeguensis TAD1 in a biotrickling filter.

The removal of NO(X) at high temperature by Chelatococcus daeguensis TAD1 in a biotrickling filter was studied. Media components of the recycling liquid were screened using Plackett-Burman design and then were optimized using response surface methodology, which enhanced the efficiency of nitrate removal by TAD1. The optimal medium was used to perform long-term experiments of NO(X) removal in a biotrickling filter under high concentrations of O(2) and NO in simulated flue gas. Results showed that the biotrickling filter was able to consistently remove 80.2-92.3% NO(X) when the inlet NO concentration was 600ppm under the conditions of oxygen concentration ranging between 2% and 20% and empty bed residence time (EBRT) being 112.5s. Analyses by polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) indicated that TAD1 was always predominant in the biofilm under a flue gas environment. Overall, the present study demonstrated that utilizing a biotrickling filter inoculated with the aerobic denitrifier TAD1 to remove NO(X) at high temperature was practically feasible.