Screening and identification of polyhydroxyalkanoates producing bacteria and biochemical characterization of their possible application

Abstract

Polyhydroxyalkanoates (PHAs) accumulating bacteria were isolated under various selective conditions such as pH, salt concentrations and types of heavy metal. Fifty strains of bacterial isolates were found to belong to Bacillus, Proteus, Pseudomonas, Aeromonas, Alcaligenes and Chromobacterium, based on phenotypical features and genotypic investigation. Only twenty fi ve bacterial isolates were selected and observed for the production of PHAs. Interestingly, bacteria belonging to Firmucutes Bacillus sp. produced a high amount of PHAs. The maximum PHAs were accumulated by B. licheniformis PHA 007 at 68.80% of dry cell weight (DCW). Pseudomonas sp., Aeromonas sp., Alcaligenes sp. and Chromobacterium sp. were recorded to produce a moderate amount of PHAs, varying from 10.00 44.32% of DCW. The enzymatic activity was preliminarily analyzed by the ratio of the clear zone diameter to colony diameter. Bacillus gave the highest ratio of hydrolysis zone which corresponds to the highest hydrolytic enzyme activities. Bacillus licheniformis PHA 007 had the highest lipase and protease activity at 2.1 and 5.1, respectively. However, the highest amylase activity was observed in Bacillus sp. PHA 023 at 1.4. Determination of metabolic characteristics was also investigated to check for their ability to consume a wide range of substrates. Bacillus, Aeromonas sp. and Alcaligenes sp. had great ability to utilize a variety of substrates. To decrease high PHA cost, different sources of cheap substrates were tested for the production of PHAs. Bacillus cereus PHA 008 gave the maximal yield of PHA production (64.09% of DCW) when cultivated in anaerobically treated POME. In addition, the accumulation of PHA copolymers such as 3-hydroxyvalerate and 3-hydroxyhexanoate was also observed in Bacillus and Pseudomomas sp. strain 012 and 045, respectively. Eight of the nine isolates accumulated a signifi cant amount of PHAs when inexpensive carbon sources were used as substrates. Here it varied from 1.69% of DCW by B. licheniformis PHA 007 to 64.09% of DCW by B. cereus PHA 008.

Class IV polyhydroxyalkanoate (PHA) synthases and PHA-producing Bacillus

“…A number of Bacillus species, but not all, can accumulate PHA in their cells under unbalanced growth conditions. The Bacillus species reported as native producers of PHA are as follows: (Yilmaz et al 2005;Kaynar and Beyatli 2009;Sangkharak and Prasertsan 2012;Kumar et al 2013;etc.). The highest level of PHA accumulation reported so far is 88.7 wt% of dry cell by using B. licheniformis M2-12 (Sangkharak and Prasertsan 2013).…”

Bacterial polyhydroxyalkanoates-eco-friendly next generation plastic: Production, biocompatibility, biodegradation, physical properties and applications

“…Further, Koller et al have suggested to link ecology with economy, because bacteria residing at ecological niches like estuarine sediments, marine microbial mats, rhizosphere, groundwater sediments and engineered ecosystems with fluctuating nutrient contents support the population actively involved in PHA accumulation to meet the metabolic energy requirements during starvation period and this concept can be implemented industrially to reduce the cost of biopolymers commercially with sustainable production processes (268). Therefore, it is economical to use naturally producing microorganism due to safety and constant productivity rate, and there is great potential for producing PHAs in low-cost substrates, which can reduce PHAs production costs, because the cost of substrate is the most important factor for PHAs production (269)(270)(271). Moreover, novel-constituent polymers will reduce the unfavorable characteristics of PHA.…”

“…From an economical point of view, the price of the product ultimately depends on the substrate (mainly carbon source) cost, PHA yield on the substrate and the efficiency of product formulation in the downstream processing (31,107). It is a prerequisite to standardize all the fermentation conditions, and physical and chemical parameters for the successful implementation of commercial PHA production systems (269)(270)(271)(272)(273). PHAs production costs can be reduced by several means, including the use of cheap substrates, such as whey, favored in countries with important dairy industries, or the enhancement of product yield, for example by using recombinant E. coli (7,35,267,274).…”

“…and Alcaligenes sp. had ability to produce high amounts (2-6.58 g/l) of PHAs and high levels of hydrolytic enzyme activities which may result in efficient utilization of municipal wastewater, palm oil mill effluent, glycerol and molasses, and its conversion into PHAs with a variety of PHA monomers (270).…”

Isolation, Cloning and Sequencing of Poly 3-Hydroxybutyrate Synthesis Genes from Local Strain of Bacillus cereus mm7 and Expression them in E. coli

“…Furthermore, Ghate et al [8] isolated different Bacillus species for the production of polyhydroxybutyrate (PHB) from soil samples. Sangkharak et al [9] isolated twenty five Bacillus sp. strains that were able to accumulate polyhydroxyalkanoates (PHAs).…”