Recent advances in genetic engineering have helped scientists engineer certain microorganisms, such as
and yeast, for large-scale carotenoid production. For example, an engineered
has been constructed to synthesize zeaxanthin from lycopene using two fusion protein-mediated substrate channels and introduce tunable intergenic regions to express
genes encode for the enzyme lycopene β-cyclase and a β-carotene hydroxylase, respectively
.
was genetically engineered for the production of lycopene by many modifications; firstly, its
. Secondly, the
gene, which blocked the competitive pentose phosphate pathway and reinforced the methyl erythritol phosphate pathway
. Thus, genetically engineered micro-organisms can be extensively employed for the large-scale production of pigments with many therapeutic and industrial uses.
Since the discovery of antibiotics, the fatality due to bacterial infections has drastically reduced. Over the past decades, not only has the average lifespan of human beings increased, but we have also learned how to tackle health care emergencies. Thanks to the ever-expanding pharma industry, which invest in the research and development of new drugs and manage their production and circulation amongst the human population. However, as years pass by, our knowledge of modern medicine still stands incompetent in front of the present-day challenges. Due to the injudicious circulation of heavy antibiotics, multidrug-resistant (MDR) strains of pathogenic microorganisms have developed. This is one of the challenges that have rendered us helpless. Another one is the unsolved puzzles of diseases, such as cancer, which lay an irreversible impact on patients and their families. To tackle the serious issues of antimicrobial resistance and expensive healthcare, the pharma industry was compelled to look into a new direction—‘bacterial pigments’. Bacterial pigments in recent years of research have revalued their importance; they might be the next big breakthrough in the field of modern medicine.
8. Application of Microbial Pigments in Food Industries
Vibrant and colourful food items appeal to the senses of people of all age groups. There are pieces of evidence that prove the early Egyptian and Roman empires used natural food colours in their food to make their product more appealing
[29]. Food industries have also begun to rely on food colourants, and to keep costs down, they encourage the use of synthetically manufactured food colourants due to their stability and low price. However, synthetic food colours are made out of the by-products of petroleum wastes and are not health-benefiting. In some cases, the long term use of artificial colouring can ill impact the health of the consumers
[30][31]. Plant-based colouring agents are often costly and unstable; hence, researchers are shifting their focus towards bacterial pigments since they are more stable and easier to produce than plant-based pigments
[32]. However, when compared to synthetic pigments, microbial pigments exhibit reduced stability in specific environmental circumstances (light, pH, oxygen, UV, temperature), which causes them to reduce their shelf-life and lose their colour over time
[32][33]. Thus, certain techniques have been developed, such as micro-encapsulation, preparations of nanoemulsion, or nanoformulations, which increase the market value of microbial pigments making them more durable for industrial applications
[34][35][36]. With the knowledge of recombinant DNA technology, bacterial pigment production can be increased multifold. Microorganisms produce pigments, such as flavin, melanins, monascins, violaceins, carotenoids, quinies, and many others
[13], which can be employed in the modern food industry, not only as colourants, but also as pro stabilizers due to their free radical scavenging activity
[37]. For example, a pinkish-red pigment, astaxanthin, produced by the bacteria
Agrobacterium aurantiacum and
Paracoccus carotinifaciens, is an excellent antioxidant, which, when used as a colourant in food items, not only imparts an attractive colour, but also increases the shelf life of the product, thereby acting as a preservative as well
[38]. Similar to astaxanthin is canthaxanthin, produced by
Bradyrhizobium Sepp. This orange-coloured pigment is also a potent antioxidant currently being used in the food industry
[39].
As discussed earlier, bacterial pigments also have many therapeutic properties associated with them; thus, the inclusion of such pigments in food products will enhance the visual appeal of the foods and fortify them with essential medicinal properties. For example, Heptyl prodigiosinis, a pink anti-plasmodial pigment (isolated from α-Proteobacteria), prodigiosin, a red anticancer pigment (isolated from
Serratia marcescenes), and pyocyanin, a proinflammatory green pigment (isolated from
Pseudomonas spp.)
[40], are a few examples of the pigments already being used by the food industry, which are also having therapeutic applications. In addition, many pigments, such as staphyloxanthin (isolated from
Staphylococcus aureus), trypanthirin (isolated from
Cytophaga/
Flexibacteria AM13,1 Strain)
[41], and undecylprodigiosin (isolated from
Serratia marcescenes), are under laboratory analysis and soon might be used in the food industry as a non-toxic, therapeutic food colourant. With more research investigations directed towards the search for new bacterial pigments and soon, a new class of immune-fortified foods might gain popularity, as these foods would be not only appealing, but also impart therapeutic immunity to the consumer, especially in the prevailing times where humanity is more than ever prone to infectious diseases and lifestyle disorders.
9. Application of Microbial Pigments in the Cosmetic Industry
Since synthetic dyes have toxicity and carcinogenicity issues, cosmetic industries also switch to safer alternatives. One of these is low cost yet highly efficient bacterial pigments. Most of these pigments are isolated from marine bacteria or extremophiles
[42]. The degradation of the dermal and epidermal layer’s extracellular matrix is the primary factor behind the skin’s ageing, which is mainly controlled by the intrinsic factor (genetics and personal diet). However, the external environment (smoke, pollution, UV exposure, weather, etc.) contributes to the premature ageing of the skin. Amongst all the known pigments, β-carotenoids are the active ingredients used in anti-ageing creams. Carotenoid is a lipid-soluble pigment with a characteristic carrot-like orange colour produced by
Deinococcus radiodurans [43], having an excellent capacity to prevent the production of ROS, which causes extensive damage to cells. Therefore, it is used in anti-ageing formulations, such as provitamin A. The anti-ageing property of cosmetics is due to high percentages of antioxidants. One of the pigments produced by
Haematococcus pluvialis is astaxanthin, which is known to have excellent antioxidant properties. These antioxidants scavenge upon the free radicals produced by the cells
[44]. The other two most commonly used antioxidants in the cosmetics industry are; myxol and saproxanthin. These pigments are members of the carotenoid family and are isolated from strains of marine bacteria belonging to the
Flavobacteriaceae family
[45].
Prolonged exposure to UV radiations causes dermatoheliosis, also known as photo-ageing
[46]. In the long run, UV exposure can also cause DNA damage and can cause skin cancer. Hence, nowadays, moisturizersizers and sunscreens add pigments that reprimand the UV damage. Most of the extremophiles produce pigments that assist them in avoiding DNA damage. Scytonemin is one such pigment, a UV-A inducible pigment made by cyanobacteria that may aid in UV radiation protection due to its potential for absorption in the UV-A and UV-B range
[47][48].
The modern-day cosmetic industry relies on bacterial pigments as effective preservatives since chemical preservatives can be harmful or toxic to the user and might decompose into undesirable compounds, rendering the product ineffective. A polyacetylene pigment, falcarindiol, obtained from the chloroform extract of
Crithmum maritimum [49], has antimicrobial effects against bacteria
Micrococcus luteus and
Bacillus cereus, thereby imparting long shelf life to the product. However, bacterial pigments have still not been profoundly studied for their skin whitening, but astaxanthin, a carotenoid, is known to have depigmentation properties that aid in the lightening of the skin spots developed due to skin ageing by reducing melanin production
[50]. Therefore, companies in cosmetic industries are investing more in researching marine bacterial pigments and utilization in preparing cosmetic concoctions, which are safe and more efficient in function.
10. Application of Microbial Pigments in Textile Industry
Since they are non-carcinogenic and safe for the environment, the textile industry now favours microbial pigments. Synthetic colours can have a harmful impact on your health in a number of ways, including skin responses and the emission of potentially dangerous compounds during synthesis. Prodigiosins, which are bright red in colour isolated from
Vibrio sp., can be used for dyeing silk, wool, nylon and acrylics
[51]. Additionally, prodigiosin, produced by
Serratia marcescens SB08, has found its potential use as a natural dye for various fabrics, such as acrylics, silk, polyesters and cotton
[52]. The fabrics dyed with such microbial-derived pigments also retained anti-microbial activities against microbes, such as
P. aeruginosa,
E.coli, and
Bacillus subtilis, making the fabrics much safer for human use.