Cyanobacteria as a Promising Alternative for Sustainable Environment: Synthesis of Biofuel and Biodegradable Plastics

Abstract

With the aim to alleviate the increasing plastic burden and carbon footprint on Earth, the role of certain microbes that are capable of capturing and sequestering excess carbon dioxide (CO₂) generated by various anthropogenic means was studied. Cyanobacteria, which are photosynthetic prokaryotes, are promising alternative for carbon sequestration as well as biofuel and bioplastic production because of their minimal growth requirements, higher efficiency of photosynthesis and growth rates, presence of considerable amounts of lipids in thylakoid membranes, and cosmopolitan nature. These microbes could prove beneficial to future generations in achieving sustainable environmental goals. Their role in the production of polyhydroxyalkanoates (PHAs) as a source of intracellular energy and carbon sink is being utilized for bioplastic production. PHAs have emerged as well-suited alternatives for conventional plastics and are a parallel competitor to petrochemical-based plastics. Although a lot of studies have been conducted where plants and crops are used as sources of energy and bioplastics, cyanobacteria have been reported to have a more efficient photosynthetic process strongly responsible for increased production with limited land input along with an acceptable cost. The biodiesel production from cyanobacteria is an unconventional choice for a sustainable future as it curtails toxic sulfur release and checks the addition of aromatic hydrocarbons having efficient oxygen content, with promising combustion potential, thus making them a better choice. Here, we aim at reporting the application of cyanobacteria for biofuel production and their competent biotechnological potential, along with achievements and constraints in its pathway toward commercial benefits. This review article also highlights the role of various cyanobacterial species that are a source of green and clean energy along with their high potential in the production of biodegradable plastics.

Keywords: biodegradable; biofuel; bioplastics; biopolymer; clean energy; polyhydroxyalkanoates; sustainable.

Figure 1

Mic of Cyanobacterium Anabaena sp. (A) Phase contrast microscopic images, (B) scanning electron microscopic (SEM) images, and (C) fluorescence microscopic image showing auto-fluorescent pigments.

Figure 2

(A) Schematic representation of cyanobacterial metabolic pathways leading to biofuel (bioethanol) derivatives viz. ethanol, butanol, isobutanol, isopropanol, 2,3-butanediol, and fatty alcohol; all derived from Calvin cycle and associated intermediate biomolecules (especially pyruvate). (B) Synthesis of PHA copolymers (PHB and PHBV) through enzyme-mediated 3-step pathway i.e., condensation, reduction, and polymerization with precursor acetyl-CoA molecules and through fatty acid β-oxidation pathway.

Figure 3

From the first generation to the fourth generation: overview of steps involved in biofuel production technology.

Figure 4

Structure of PHAs (polyhydroxyalkanoates). In homopolymers, m can vary from 1 to 3 {polyhydroxybutyrate (PHB) - m = 1}, n can vary from 100 to 30,000 monomers, where R is a varied chain length alkyl group.