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Influence of growth stage on activities of polyhydroxyalkanoate (PHA) polymerase and PHA depolymerase in Pseudomonas putida U.

Ren Q, de Roo G, Witholt B, Zinn M, Thöny-Meyer L - BMC Microbiol. (2010)

Bottom Line: In addition, it was found that after eliminating phasins (PhaF and PhaI) from the granules PhaC activity decreased further.It was found that in P. putida PhaC and PhaZ are concomitantly active, resulting in parallel synthesis and degradation of PHA.Moreover PhaC activity was found to be decreased, whereas PhaZ activity increased during growth.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory for Biomaterials, Swiss Federal Laboratories for Materials Science and Technology (Empa), CH-9014 St, Gallen, Switzerland. qun.ren@empa.ch

ABSTRACT

Background: Medium chain length (mcl-) polyhydroxyalkanoates (PHA) are synthesized by many bacteria in the cytoplasm as storage compounds for energy and carbon. The key enzymes for PHA metabolism are PHA polymerase (PhaC) and depolymerase (PhaZ). Little is known of how mcl-PHA accumulation and degradation are controlled. It has been suggested that overall PHA metabolism is regulated by the β-oxidation pathway of which the flux is governed by intracellular ratios of [NADH]/[NAD] and [acetyl-CoA]/[CoA]. Another level of control could relate to modulation of the activities of PhaC and PhaZ. In order to investigate the latter, assays for in vitro activity measurements of PhaC and PhaZ in crude cell extracts are necessary.

Results: Two in vitro assays were developed which allow the measurement of PhaC and PhaZ activities in crude cell extracts of Pseudomonas putida U. Using the assays, it was demonstrated that the activity of PhaC decreased 5-fold upon exponential growth on nitrogen limited medium and octanoate. In contrast, the activity of PhaZ increased only 1.5-fold during growth. One reason for the changes in the enzymatic activity of PhaC and PhaZ could relate to a change in interaction with the phasin surface proteins on the PHA granule. SDS-PAGE analysis of isolated PHA granules demonstrated that during growth, the ratio of [phasins]/[PHA] decreased. In addition, it was found that after eliminating phasins (PhaF and PhaI) from the granules PhaC activity decreased further.

Conclusion: Using the assays developed in this study, we followed the enzymatic activities of PhaC and PhaZ during growth and correlated them to the amount of phasins on the PHA granules. It was found that in P. putida PhaC and PhaZ are concomitantly active, resulting in parallel synthesis and degradation of PHA. Moreover PhaC activity was found to be decreased, whereas PhaZ activity increased during growth. Availability of phasins on PHA granules affected the activity of PhaC.

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SDS-PAGE analysis of PHA granules isolated in different growth phases. Lanes: Molecular weight marker (kD, lane 1), PHA granules isolated from P. putida U after 8 hours (lane 2), 14 hours (lane 3), 20 hours (lane 4) and 25 hours (lane 5) of growth on octanoate. Increasing amounts of PHA granules were applied: 0.1 mg (lane 2), 0.5 mg (lane 3), 1 mg (lane 4) and 1.5 mg (lane 5), respectively. Experiments were performed three times. For different cultivations, the absolute values regarding total amount of PHA granule-attached proteins had variations due to sample taken at different time points; however, PHA reganule-attached proteins exhibited similar pattern relative to cell growth in these three experiments. In this study, only the results obtained from one experiment were presented.
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Figure 5: SDS-PAGE analysis of PHA granules isolated in different growth phases. Lanes: Molecular weight marker (kD, lane 1), PHA granules isolated from P. putida U after 8 hours (lane 2), 14 hours (lane 3), 20 hours (lane 4) and 25 hours (lane 5) of growth on octanoate. Increasing amounts of PHA granules were applied: 0.1 mg (lane 2), 0.5 mg (lane 3), 1 mg (lane 4) and 1.5 mg (lane 5), respectively. Experiments were performed three times. For different cultivations, the absolute values regarding total amount of PHA granule-attached proteins had variations due to sample taken at different time points; however, PHA reganule-attached proteins exhibited similar pattern relative to cell growth in these three experiments. In this study, only the results obtained from one experiment were presented.

Mentions: To understand the observed decrease of PhaC activities and increase of PhaZ activities, PHA granules were isolated from P. putida U after 8, 14, 20 and 25 hours of growth on octanoate. All four granule preparations were analyzed by SDS-PAGE in order to see differences in protein composition (Figure 5). No significant changes could be observed between the different granule preparations, except that the amount of the phasin PhaF was slightly decreased after 14 hours. When the amount of PHA granules which were loaded on the SDS-polyacrylamide gel was taken into account, it appeared that isolated granules harvested after 25 hours of growth contained much less proteins as compared to PHA granules harvested after 8 hours. This indicated that PHA granules harvested at a later growth stage had smaller surface areas for protein binding. Furthermore, there was an increased background of "contaminating" proteins at later growth stages (Figure 5), possibly caused by non-specific binding to the PHA surface [26].


Influence of growth stage on activities of polyhydroxyalkanoate (PHA) polymerase and PHA depolymerase in Pseudomonas putida U.

Ren Q, de Roo G, Witholt B, Zinn M, Thöny-Meyer L - BMC Microbiol. (2010)

SDS-PAGE analysis of PHA granules isolated in different growth phases. Lanes: Molecular weight marker (kD, lane 1), PHA granules isolated from P. putida U after 8 hours (lane 2), 14 hours (lane 3), 20 hours (lane 4) and 25 hours (lane 5) of growth on octanoate. Increasing amounts of PHA granules were applied: 0.1 mg (lane 2), 0.5 mg (lane 3), 1 mg (lane 4) and 1.5 mg (lane 5), respectively. Experiments were performed three times. For different cultivations, the absolute values regarding total amount of PHA granule-attached proteins had variations due to sample taken at different time points; however, PHA reganule-attached proteins exhibited similar pattern relative to cell growth in these three experiments. In this study, only the results obtained from one experiment were presented.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2959000&req=5

Figure 5: SDS-PAGE analysis of PHA granules isolated in different growth phases. Lanes: Molecular weight marker (kD, lane 1), PHA granules isolated from P. putida U after 8 hours (lane 2), 14 hours (lane 3), 20 hours (lane 4) and 25 hours (lane 5) of growth on octanoate. Increasing amounts of PHA granules were applied: 0.1 mg (lane 2), 0.5 mg (lane 3), 1 mg (lane 4) and 1.5 mg (lane 5), respectively. Experiments were performed three times. For different cultivations, the absolute values regarding total amount of PHA granule-attached proteins had variations due to sample taken at different time points; however, PHA reganule-attached proteins exhibited similar pattern relative to cell growth in these three experiments. In this study, only the results obtained from one experiment were presented.
Mentions: To understand the observed decrease of PhaC activities and increase of PhaZ activities, PHA granules were isolated from P. putida U after 8, 14, 20 and 25 hours of growth on octanoate. All four granule preparations were analyzed by SDS-PAGE in order to see differences in protein composition (Figure 5). No significant changes could be observed between the different granule preparations, except that the amount of the phasin PhaF was slightly decreased after 14 hours. When the amount of PHA granules which were loaded on the SDS-polyacrylamide gel was taken into account, it appeared that isolated granules harvested after 25 hours of growth contained much less proteins as compared to PHA granules harvested after 8 hours. This indicated that PHA granules harvested at a later growth stage had smaller surface areas for protein binding. Furthermore, there was an increased background of "contaminating" proteins at later growth stages (Figure 5), possibly caused by non-specific binding to the PHA surface [26].

Bottom Line: In addition, it was found that after eliminating phasins (PhaF and PhaI) from the granules PhaC activity decreased further.It was found that in P. putida PhaC and PhaZ are concomitantly active, resulting in parallel synthesis and degradation of PHA.Moreover PhaC activity was found to be decreased, whereas PhaZ activity increased during growth.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory for Biomaterials, Swiss Federal Laboratories for Materials Science and Technology (Empa), CH-9014 St, Gallen, Switzerland. qun.ren@empa.ch

ABSTRACT

Background: Medium chain length (mcl-) polyhydroxyalkanoates (PHA) are synthesized by many bacteria in the cytoplasm as storage compounds for energy and carbon. The key enzymes for PHA metabolism are PHA polymerase (PhaC) and depolymerase (PhaZ). Little is known of how mcl-PHA accumulation and degradation are controlled. It has been suggested that overall PHA metabolism is regulated by the β-oxidation pathway of which the flux is governed by intracellular ratios of [NADH]/[NAD] and [acetyl-CoA]/[CoA]. Another level of control could relate to modulation of the activities of PhaC and PhaZ. In order to investigate the latter, assays for in vitro activity measurements of PhaC and PhaZ in crude cell extracts are necessary.

Results: Two in vitro assays were developed which allow the measurement of PhaC and PhaZ activities in crude cell extracts of Pseudomonas putida U. Using the assays, it was demonstrated that the activity of PhaC decreased 5-fold upon exponential growth on nitrogen limited medium and octanoate. In contrast, the activity of PhaZ increased only 1.5-fold during growth. One reason for the changes in the enzymatic activity of PhaC and PhaZ could relate to a change in interaction with the phasin surface proteins on the PHA granule. SDS-PAGE analysis of isolated PHA granules demonstrated that during growth, the ratio of [phasins]/[PHA] decreased. In addition, it was found that after eliminating phasins (PhaF and PhaI) from the granules PhaC activity decreased further.

Conclusion: Using the assays developed in this study, we followed the enzymatic activities of PhaC and PhaZ during growth and correlated them to the amount of phasins on the PHA granules. It was found that in P. putida PhaC and PhaZ are concomitantly active, resulting in parallel synthesis and degradation of PHA. Moreover PhaC activity was found to be decreased, whereas PhaZ activity increased during growth. Availability of phasins on PHA granules affected the activity of PhaC.

Show MeSH
Related in: MedlinePlus