- (DESACTIVADA) Services
- (DESACTIVADA) Contact us
PHA-producing bacteria accumulate PHA within their cell. For these bacteria, PHA serves as carbon and energy reserves. In a similar way, humans store glycogen and fat. However, these bacteria only produce PHA when it is required for them to do so. Therefore, the biotechnology of PHA production lies in the creation of the conditions which induce optimal PHA production.
Depending on the type of process, PHA-producing bacteria is either isolated or grown from a natural source. The bacteria are cultured to grow to its log and stationary stage after which the cells are transferred to a different medium or the conditions in the bioreactor are adjusted to stimulate PHA production. These are carried out in batch or fed-batch systems at an industrial scale. The total time is around 24-72 hours on average after which the cell can accumulate around 52%- 90% PHA by dry weight.
The next stage is then to remove the bacteria from the medium slurry to extract the PHA. In most cases, the PHA is produced within the bacteria cell therefore cell lysis is carried out to break open the cell to extract the accumulated PHA. The recovery, separation, and purification stages then follow.
PHA can be obtained from bacteria using either pure or mixed culture.
Table 1 summarizes the difference between the two:
– High-purity substrate required mainly glucose
– Extremophiles like halophiles and thermophiles can be used to reduce the chance of contamination
– Relatively lower yield per bacteria cell dry weight but higher cell density
– Product is more homogenous due to the uniformity of the substrate
– Bacteria isolated and engineered for optimal PHA production
– Microbial growth occurs in a separate stage
Table 1. Comparing Mixed culture and pure culture PHA production
This is more widely used in industrial PHA production. However, the production cost is relatively high. This is in part due to the requirement for substrates of high purity which can add to around 45% of the total production cost.
The pure bacteria culture are isolated from different environments. The right cconditions are then provided to cultivate them in fermenters to promote PHA production. This method focuses on identifying a PHA-producing bacteria and engineering the bacteria for optimum PHA production.
The species most used in industrial PHA production are Alcaligenes latus Cupriavidus necator and Pseudomonas putida. Others include Paracoccus dentrificans, Pseudomonas aeruginosa and Bacillus megaterrium.
The type of bacteria PHA producer employed depends on the type of feedstock available as a cultivation medium. For example, Alcaligenes latus produces PHA optimally in cultivation mediums rich in carbon and nutrients whereas Cupriavidus necator is better suited for cultivation mediums low in essential growth nutrients like nitrogen and phosphorus. It also depends on whether a mixed of pure culture is being used as discussed in the next sections.
Saccharophagus Degradan, is a species of marine bacteria that are capable of degrading complex polysaccharides such as cellulose, alginate, chitin, starch, pectin, and xylan. One advantage of this bacteria in PHA production is the possibility of carrying out saccharification of lignocellulosic polysaccharides simultaneously with PHA production. This can reduce the production cost.
Caldimonas Taiwanensis is another strain of bacteria, a thermophile, that can produce PHA in the form of PHB granules. The advantage of this strain is the high temperature needed for the cultivation of this bacteria reduces or eliminates the risk of contamination since other microbes will not survive these extreme temperatures.
Halophites such as Haloferax mediterranei and Bacillus megaterrium have also been explored for PHA production. Because non-halophilic organisms are unable to survive in such high salt concentrations, the use of halophilic PHA-producing bacteria has the advantage of minimizing the risk of contamination. It also reduces the need for freshwater since seawater can be used.
These bacteria strains also have the added advantage of being able to survive in a wide range of temperatures and pH. One major disadvantage of using high saline mediums for PHA production is the corrosion of the fermenters and the pipes which are typically made of stainless steel. This will require modification of the system to incorporate materials like plastics and ceramics to prevent corrosion.
Bacteria strains like Bacillusm Pseudomonas, rhodococcus, and sphingobacterium are being explored for the combined bioremediation and PHA production. Some of these are genetically diverse and have versatile catabolic activities. Pseudomonas strains like P. putida for example have been observed to produce PHA from hydrocarbons such as styrene with PHA accumulation of up to 32% crude dry weight. This offers the potential for bioremediation in contaminated soil and oily sludge from oil refineries.
Recent innovations also include the chemo-biotechnological conversion of polystyrene to styrene oil followed by the conversion of the styrene oil into PHA using P. putida bacteria. Textile dye-degrading bacteria have also been identified to produce PHA.
This involves the production of PHA using open, non-sterile conditions comprising of a mixed consortium of microorganisms. This method focuses on engineering the growth environment to promote the growth and activity of the microorganism that produce PHA.
Mixed culture PHA production is based on the concept that microbes are naturally present in the environment. The types of microbes that colonize a given system depend on having the precise environmental conditions that allow those microbes to thrive over other microbes.
In mixed culture PHA production it is often necessary to have a pretreatment stage to convert the complex substrate into VFAs (Volatile fatty acids). This prevents the formation of undesired glycogen hence improving PHA yield and homogeneity. Mixed culture PHA production has been known to reach a yield of up to 90%.
The stages of Mixed culture PHA production are summarized in figure 1:
Figure 1. Flow chart of PHA production
Future polymer biotechnology is directed at making PHA production more environmentally sustainable as well as cost-effective. Approaches being adopted include for example using sea water or recycled water rather than fresh water, adopting continuous rather than processes, synchronizing PHA production with bioremediation, simultaneous hydrolysis of polysaccharides and PHA production, and engineering PHA producers for improved yield.
The current state of the art in PHA biotechnology is in the utilization of renewable waste as substrate. This is in alignment with the goal of more sustainable and cost-effective PHA production. VEnvirotech specializes in the production of bioplastic formulations incorporating PHA from organic waste. This is achieved through the development of highly efficient bacteria culture using advanced biotechnology.
VEnvirotech has developed a range of bioplastic blends incorporating PHA as well as innovative biotechnology for revaluation of organic waste into raw materials for PHA and other bioplastic formulations.
Contact us today to find out more about our products and services.