Abstract
Phasins are amphiphilic proteins involved in the regulation of the number and size of polyhydroxybutyrate (PHB) granules. The plant growth promoting bacterium Azospirillum brasilense Sp7 accumulates high quantities of bioplastic PHB as carbon and energy source. By analyzing the genome, we identified six genes that code for proteins with a Phasin_2 domain. To understand the role of A. brasilense Sp7 PhaP1 (PhaP1Abs) on PHB synthesis, the phaP1 gene (AMK58_RS17065) was deleted. The morphology of the PHB granules was analyzed by transmission electron microscopy (TEM) and the PHB produced was quantified under three different C:N ratios in cultures subjected to null or low-oxygen transfer. The results showed that PhaP1Abs is involved in PHB granules morphology and in controlling early biopolymer accumulation. Using RT-PCR it was found that phasin genes, except phaP4, are transcribed in accordance with the C:N ratio used for the growth of A. brasilense. phaP1, phaP2 and phaP3 genes were able to respond to the growth conditions tested. This study reports the first analysis of a phasin protein in A. brasilense Sp7.
Highlights
Since it was reported for the first time in 1926 (Lemoigne 1926), polyhydroxybutyrate (PHB) has been the best studied bacterial biopolymer
Two putative phasin genes are in plasmid 1: AMK58_RS17065 (Gene ID: 36110503) and AMK58_RS20955 (Gene ID: 36111302) and the other putative phasin genes are in the chromosome: AMK58_RS04265 (Gene ID: 36107916), AMK58_RS04270 (Gene ID: 36107917), AMK58_ RS07520 (Gene ID: 36108566) and AMK58_RS13850 (Gene ID: 36109844) (Additional file 1)
Phasin proteins have been mainly implicated in PHB granule stabilization which occurs due to their amphiphilic properties (Pötter and Steinbüchel 2005) that avoid the a
Summary
Since it was reported for the first time in 1926 (Lemoigne 1926), polyhydroxybutyrate (PHB) has been the best studied bacterial biopolymer. PHB exhibits similar characteristics with respect to petrochemical plastics in addition to its biodegradability and biocompatibility properties. These characteristics enable PHB convenient to reduce the use of petrochemical plastic derivatives (Madison and Huisman 1999; Anjum et al 2016). More than 300 microorganisms have been reported to be PHB-producers (Koller et al 2010; Alarfaj et al 2015). PHB-producing microorganisms synthesize PHB by three enzymatic reactions. PHB-producing microorganisms synthesize PHB by three enzymatic reactions. β-ketothiolase (PhaA) condenses two acetyl-CoA into acetoacetyl-CoA,
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