• Korean Journal of Microbiology
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• v.36 no.2
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• pp.84-90
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• 2000

Biodegradation of vanous medium-chain-length polyhydroxyalkanoates (MCL-PHAs) by an extracellular depolymerase system from Pseudomonas sp. RY-1 was investigated under laboratoly conditions. The degradation rate of the polymers was determined by quantitative clem zone technique, enzyme (turbidity) assay, and respirometry assay. Although the enzyme system secreted by Pscudomor~as sp. RY-1 was capable of degrading all MCL-PHAs tested. its secretion was influenced by the availability of secondary carbon sources. The rate of enzymatic degradation of MCL-PHAs was dependent upou the monomeric composition of the polyesters and reduced as the chain lengths of the monomer m t s in the polyesters increased. MCL-PHAs containing C-even monomer units showed faster degradation rate than MCL-PHAs containing C-odd monomer units. Respiration rates of MCL-PHAs with C-even monomer uuts were also much faster than those of MCL-PHAs with C-odd monomer units. The degmdation rate of MCL-PHAs bearing unsaturated substituents was faster than that of mcl-PHAs without functional substituents, which is suggesting the correlation between the degradation rate and the crystallinity of MCL-PHAs.

• Journal of Microbiology
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• v.45 no.2
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• pp.87-97
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• 2007

Medium-chain-length polyhydroxyalkanoates (MCL-PHAs), which have constituents with a typical chain length of $C_{6}-C_{14}$, are polyesters that are synthesized and accumulated in a wide variety of Gram-negative bacteria, mainly pseudomonads. These biopolyesters are promising materials for various applications because they have useful mechanical properties and are biodegradable and biocompatible. The versatile metabolic capacity of some Pseudomonas spp. enables them to synthesize MCL-PHAs that contain various functional substituents; these MCL-PHAs are of great interest because these functional groups can improve the physical properties of the polymers, allowing the creation of tailor-made products. Moreover, some functional substituents can be modified by chemical reactions to obtain more useful groups that can extend the potential applications of MCL-PHAs as environmentally friendly polymers and functional biomaterials for use in biomedical fields. Although MCL-PHAs are water-insoluble, hydrophobic polymers, they can be degraded by microorganisms that produce extracellular MCL-PHA depolymerase. MCL-PHA-degraders are relatively uncommon in natural environments and, to date, only a limited number of MCL-PHA depolymerases have been investigated at the molecular level. All known MCL-PHA depolymerases share a highly significant similarity in amino acid sequences, as well as several enzymatic characteristics. This paper reviews recent advances in our knowledge of MCL-PHAs, with particular emphasis on the findings by our research group.

• Journal of Microbiology and Biotechnology
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• v.22 no.3
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• pp.371-377
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• 2012

The present study describes medium-chain-length polyhydroxyalkanoates (mcl-PHAs) production by the Pseudomonas Gl01 strain isolated from mixed microbial communities utilized for PHAs synthesis. A two-step fed-batch fermentation was conducted with glucose and waste rapeseed oil as the main carbon source for obtaining cell growth and mcl-PHAs accumulation, respectively. The results show that the Pseudomonas Gl01 strain is capable of growing and accumulating mcl-PHAs using a waste oily carbon source. The biomass value reached 3.0 g/l of CDW with 20% of PHAs content within 48 h of cultivation. The polymer was purified from lyophilized cells and analyzed by gas chromatography (GC). The results revealed that the monomeric composition of the obtained polyesters depended on the available substrate. When glucose was used in the growth phase, 3-hydroxyundecanoate and 3-hydroxydodecanoate were found in the polymer composition, whereas in the PHAs-accumulating stage, the Pseudomonas Gl01 strain synthesized mcl-PHAs consisting mainly of 3-hydroxyoctanoate and 3-hydroxydecanoate. The transcriptional analysis using reverse-transcription real-time PCR reaction revealed that the phaC1 gene could be transcribed simultaneously to the phaZ gene.

• Korean Journal of Microbiology
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• v.41 no.3
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• pp.225-231
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• 2005

The characteristics of cell growth and medium-chain-length polyhydroxyalkanoate (MCL-PHA) biosynthesis of Pseudomonas chlororaphis HS21 were investigated using plant oils as the carbon substrate. The organism was efficiently capable of utilizing plant oils, such as palm oil, corn oil, and sunflower oil, as the sole carbon source for growth and MCL-PHA production. When palm oil (5 g/L) was used as the carbon source, the cell growth and MCL-PHA accumulation of this organism occurred simultaneously, and a high dry cell weight (2.4 g/L) and MCL-PHA ($40.2\;mol{\%}$ of dry cell weight) was achieved after 30 hr of batch-fermentation. The repeating unit in the MCL-PHA produced from palm oil composed of 3-hydroxyhexanoate ($7.0\;mol{\%}$), 3-hydroxyoctanoate ($45.3\;mol{\%}$), 3-hydroxydecanoate ($39.0\;mol{\%}$), 3-hydroxydodecanoate ($6.8\;mol{\%}$), and 3-hydroxytetradecanoate ($1.9\;mol{\%}$), as determined by GC/MS. Even though glucose was a carbon substrate that support cell growth but not PHA production, the conversion rate of palm oil to PHA was significantly increased when glucose was fed as a cosubstrate, suggesting that bioconversion of some functionalized carbon substrates to related polymers in P chlororaphis HS21 could be enhanced by the co-feed of good carbon substrates for cell growth. In addition, the change of compositions of repeating units in MCL-PHAs synthesized from the plant oils was markedly affected by the supplementation of acrylic acid, an inhibitor of fatty acid ${\beta}-oxidation$. The addition of acrylic acid resulted in the increase of longer chain-length repeating units, such as 3-hydroxydodecanoate and 3-hydroxytetradecanoate, in the MCL-PHAs produced. Particularly, MCI-PHAs containing high amounts of unsaturated repeating units could be produced when sunflower oil and corn oil were used as the carbon substrate. These results suggested that the alteration of PHA synthesis pathway by acrylic acid addition can offer the opportunity to design new functional MCL-PHAs and other unusual polyesters that have unique physico-chemical properties.

• Microbiology and Biotechnology Letters
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• v.32 no.2
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• pp.123-127
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• 2004

Pseudomonas sp. MBEL21 was newly isolated from soil samples and found to accumulate medium-chain-length Polyhydroxyalkanoates(MCL-PHAs) using oleic acid as a sole carbon source. Among the various nutrient limiting conditions examined, including nitrogen, sulfur and phosphorus, only phosphorus limitation supported the accumulation of MCL-PHAs up to 15 wt％ of dry cell weight in flask cultures. MCL-PHAs produced by Pseudomonas sp. MBEL21 was mainly composed of 3-hydroxy-5-cis-tetradecenoate. Fed-batch culture of Pseudomonas sp. MBEL21 by novel feeding strategies based on cell growth charcteristics was carried out under phosphorus limitation using oleic acid as a sole carbon source. The final cell concentration and PHA content of 82 g/L and 28 wt％, respectively, were obtained. Furthermore, PHA consisted of MCL-hydroxyalkanoates and 3-hydroxybutyrate could be produced using olive oil as a sole carbon source.

• Journal of Microbiology and Biotechnology
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• v.27 no.5
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• pp.990-994
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• 2017

Polyhydroxyalkanoates (PHAs) are biodegradable plastics produced by bacteria, but their use in diverse applications is prohibited by high production costs. To reduce these costs, the conversion by Pseudomonas strains of PHAs from crude sludge palm oil (SPO) as an inexpensive renewable raw material was tested. Pseudomonas putida S12 was found to produce the highest yield (~41%) of elastomeric medium-chain-length (MCL)-PHAs from SPO. The MCL-PHA characteristics were analyzed by gas-chromatography/mass spectrometry, gel permeation chromatography, and differential scanning calorimetry. These findings may contribute to more widespread use of PHAs by reducing PHA production costs.

• Biotechnology and Bioprocess Engineering:BBE
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• v.1 no.1
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• pp.51-53
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• 1996

Fed-batch culture of Pseudomonas oleovorans was carried out for the production of medium-chain-length polyhydroxyalkanoates (MCL-PHAs) using octanoate as a carbon source. Octanoate and the salt solution containing ammounium sulfate and magnesium sulfate were intermittently fed in the course of fermentation. Cell mass and PHA concentrations of 42.8 and 16.8g/L, respectively, could be obtained in 40 h. The PHA content and the PHA productivity were 39.2% and 0.42 g PHA/L-h, respectively. The yields of cell mass and PHA were 0.71 g dry cell mass/g octanoate and 0.28g PHA/g octanoate, respectively. Therefore, octanoate can be used for the production of MCL-PHAs to a high concentration with high productivity.

• Korean Journal of Microbiology
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• v.48 no.3
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• pp.200-206
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• 2012

A bacterial strain capable of synthesizing polyhydroxyalkanoates (PHAs) with an unusual pattern of monomer units was isolated from activated sludge using the enrichment culture technique. The organism, identified as Pseudomonas aeruginosa P-5, produced polyesters consisting of 3-hydroxyvalerate and medium-chain-length (MCL) 3-hydroxyalkanoate monomer units when $C_{-odd}$ alkanoic acids such as nonanoic acid and heptanoic acid were fed as the sole carbon source. Solvent fractionation experiments using chloroform and hexane revealed that the 3-hydroxyalkanoate monomer units in these polyesters were copolymerized. The molar concentration of 3-hydroxyvalerate in the polyesters produced were significantly elevated up to 26 mol% by adding 1.0 g/L valeric acid as the cosubstrate. These copolyesters were sticky with low degrees of crystallinity. The PHA synthase genes were cloned, and the deduced amino acid sequences were determined. P. aeruginosa P-5 possessed genes encoding MCL-PHA synthases (PhaC1 and PhaC2) but lacked the short-chain-length PHA synthase gene, suggesting that the MCL-PHA synthases from P. aeruginosa P-5 are uniquely active for polymerizing (R)-3-hydroxyvaleryl-CoA as well as MCL (R)-3-hydroxyacyl-CoAs.

• Journal of Microbiology
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• v.39 no.2
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• pp.139-141
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• 2001

Medium-chain length polyhydrexyalkanoic acids (MCL-PHAs) degrading bacterium was isolated from the soil. The bacterium was identified as Janthinobacterium lividum by its biochemical properties, cell membrane fatty acids composition, and 16S rDNA sequence analysis. The bacterium showed a similarity of 0.911 with J. lividum according to the cell membrane fatty acids analysis and a similarity of 97% in the 16S rDNA requence analysis. Culture supernatant of the bacterium skewed the highest depolymerase activity toward polyhydroxynonanoic acid (PHN) that did not degrade the poly-$\beta$-hydroxybutyric acid (PHB). The esterase activity was also detected with p-nitrophenyl (PNP) esters of fatty acids such as PNP-dodecanoic PNP-dodecanoic acid, PNP-decanoic acid, and PNP-hexanoic acid.

• Journal of Microbiology and Biotechnology
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• v.8 no.5
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• pp.540-542
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• 1998

Five microorganisms capable of degrading an aromatic medium-chain-length polyhydroxyalkanoate ($PHA_{MCL}$), poly(3-hydroxy-5-phenylvalerate) (PHPV), were isolated from wastewater-treatment sludge. Among the isolates, JS02 showed degrading activity consistantly during several transfers. The isolate JS02 could hydrolyze another aromatic MCL copolyester, poly(3-hydroxy-5-phenoxyvalerate-co-3-hydroxy-7-phenoxyheptanoate), ［P(5POHV-co-7POHH)］, and other short-chain-length PHAs ($PHA_{SCL}) such as poly(3-hydroxybutyrate) ［P3(HB)］, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) ［P(3 HB-co-4 HB)］, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) ［P(3HB-co-3HV)］ with relatively low activity. The culture supernatant of JS02 showed hydrolyzing activity for the p-nitrophenyl esters of fatty acids.