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Microbial Recycling of ‘Sustainable’ Bioplastics A Rational Approach?
Published in Ederio Dino Bidoia, Renato Nallin Montagnolli, Biodegradation, Pollutants and Bioremediation Principles, 2021
Mansi Rastogi, Sheetal Barapatre
Formation of clear zones and estimating the zone diameters formed in petri plates where bioplastic serves as a sole source of carbon for bacterial or fungal colony indicates bioplastic degradation is possible using isolated microbes (Emadian et al. 2017, Trivedi et al. 2016, Brodhagen et al. 2015). Further observations using scanning electron microscope (SEM) confirm the alterations in the polymeric structure as achieved by microbial amendment to the plastic biodegradation process (Shen et al. 2015). Besides this, Fourier Transform Infrared (FTIR) spectroscopy can also be used to identify variation in bond intensity caused by microbial degradation (Phukon et al. 2012). Cupriavidus necator and Pseudomonas chlororaphis have been found to accelerate decomposition of bioplastics manufactured from Polylactid acid (PLA).
Syngas as a Sustainable Carbon Source for PHA Production
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Véronique Amstutz, Manfred Zinn
Another category of bacteria that could be considered as potential candidates for syngas bioconversion to PHA is hydrogen-oxidizing bacteria. They can facultatively grow on a CO2 and H2 gas mix, in the presence of O2. The concentration of O2 needs to remain relatively low (micro-aerobic conditions) to avoid the inhibition of hydrogenase activity. Similarly, CO can affect cell energy intake by strongly binding to the active centers of hydrogenases. However, some hydrogen-oxidizing bacteria were reported to be carbon monoxide tolerant. This includes Ralstonia eutropha B5786 [91]. Bacteria of the Cupriavidus necator (this includes R. eutropha B5786) genera are generally recognized to be efficient PHA producers. They produce PHA from the acetyl-CoA intermediate using the same three enzymes as in R. rubrum (3-ketothiolase, acetoacetyl-CoA reductase, and PHB synthase). For R. eutropha B5786, it was observed that in the presence of CO, both growth metabolism and PHB accumulation capacities remain unchanged. Indeed, increasing the concentration of CO from 0 to 20 vol% only slightly decreased the final biomass concentration (from 20 to 17.5 g/L) and PHA content (from 76.4 to 72.8 wt.-%) in batch cultures [91]. It is interesting to note that the respective activity of hydrogenase and cytochrome oxidase increased when the CO concentration rose. Finally, it was observed that this bacterium was able to use CO as a substrate but only at low rates (30–50 µmol CO min–1 mgprotein–1).
Expression and cloning of catA encoding a catechol 1,2-dioxygenase from the 2,4-D-degrading strain Cupriavidus campinensis BJ71
Published in Preparative Biochemistry & Biotechnology, 2020
Lizhen Han, Sen Chen, Jing Zhou
The biodegradation pathway of 2,4-D, a widely used phenoxy herbicide, has been extensively characterized in Cupriavidus necator JMP134 and Pseudomonas strains.[27] In most cases, catabolism of 2,4-D is starts with the formation of 3,5-dichlorocatechol from the products of the 2,4-D-dioxygenase (tfdA) and 2,4-dichlorophenol hydroxylase (tfdB).[28] Chlorocatechol 1,2-dioxygenase, encoded by the tfdC gene, is the third enzyme involved in the 2,4-D degradation pathway and catalyzes ortho- or meta-cleavage of dichlorocatechol to produce 2,4-dichloro-cis, cis-muconate.[29] Although 2,4-D is thus well known to be degraded by microorganisms via the first intermediate compound 2,4-dichlorophenol (2,4-DCP), some studies have shown that 2,4-D is also degraded via p-chlorophenoxyacetic acid as the first intermediate compound. Balajee and Mahadevan[30] have reported that Azotobacter chroococcum first converts 2,4-D to 4-chlorophenoxyacetic acid by eliminating a chlorine molecule via 2,4-D dehalogenase, with subsequent conversion to 4-chlorophenol and 4-chlorocatechol using 4-chlorophenoxyacetate monooxygenase and 2,4-dichlorophenol hydroxylase (tfdB). Finally, 4-cholorcatechol is degraded to cis, cis-3-chloromuconate by ortho-cleavage using the enzyme 4-chlorocatechol 1,2-dioxygenase.[31] Cámara et al.[32] have reported that C12OcatA and C12OsalD convert 4-chlorocatechol into 3-chloro-muconate with different enzyme activities in Pseudomonas sp. strain MT1. In our previous study, we found that TfdA from BJ71 not only successfully used 2,4-D, but also catalyzed 4-chlorophenoxyacetic acid as a substrate with 34% relative enzyme activity.[33] In this study, CatA from BJ71 could use 4-chlorocatechol as a substrate. In addition, our whole-genome sequencing of BJ71 (unpublished data) revealed the genomic presence of 2,4-D dehalogenase and tfdB, but the tfdC gene was not detected and could not be amplified using reported primers. We thus tentatively propose that the first step of 2,4-D degradation in Cupriavidus campinensis BJ71 takes place via p-chlorophenoxyacetic acid, with subsequently encoded products of tfdA catalyzing 4-chlorophenoxyacetic acid into 4-chlorophenol, with the CatA enzyme using 4-chlorocatechol as substrate. To confirm this hypothesis, more experiments are needed.