1
Introduction to Microbial Colorants

Luqman Jameel Rather1*, Shazia Shaheen Mir2 and Zeenat Islam3

1College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, PR China

2Laboratory Medicine Department, Faculty of Applied Medical Sciences, Al-Baha University, Al-Baha, Saudi Arabia

3Advanced Research Laboratory, Department of Zoology, School of Life Sciences, University of Kashmir, Srinagar, Jammu & Kashmir, India

Abstract

Microbial pigments have emerged as fascinating compounds with diverse applications, capturing the attention of researchers and industries alike. Developing microbial pigments poses a significant challenge, given the availability of cheap synthetic dyes in the market. Nevertheless, the adverse effects of the majority of azo and benzidine synthetic dyes have prompted numerous scientists and experts to redirect their focus toward more environmentally friendly methods of dye production. This chapter delves into the world of microbial pigments, offering an introduction that explores their significance, classification, structure, and applications. The discussion begins by highlighting the pivotal roles these pigments play in various biological processes, underscoring their ecological and industrial importance. A comprehensive examination of the classification of microbial pigments sheds light on the diversity present within microbial communities, showcasing the wide array of colors produced by bacteria, fungi, and other microorganisms. Furthermore, the chapter delves into the intricate structures of microbial pigments, unraveling the molecular architectures that contribute to their unique and vibrant hues. Understanding the structural nuances opens avenues for manipulation and optimization, crucial for both scientific exploration and practical applications. The latter part of the chapter navigates through the myriad applications of microbial pigments, ranging from the traditional realms of dyeing to modern applications in food, cosmetics, medicine, and textiles. By exploring the multifaceted roles of microbial pigments, this chapter aims to provide a holistic view of their potential, paving the way for further research and innovative utilization in diverse fields.

Keywords: Natural dyes, microbial colorants, biocompatible, biodegradable, textile coloration, food applications

1.1 Background and Significance

Humans have always been attracted by colors and employed natural resources from plants, animals, and minerals and their waste byproducts to color synthetic and natural textiles [1]. The advent of the synthetic colorant "Mauveine" in 1856 by W.H. Perkin, together with its subsequent proliferation and use, made natural colorants/dyes obsolete and only a small number of craftsmen and crafters continued to use them [2]. Researchers have been encouraged to investigate alternative dye sources to address the ecological and healthrelated issues associated with azo and benzidine dyes [3, 4]. The aim is to reduce the textile industry's reliance on dangerous synthetic colors and minimize their impact. As a reaction to this, several governments implemented stringent limitations on the utilization of synthetic dyes, leading to a spike in the utilization of natural dyes [5, 6]. These natural dyes have emerged as promising alternatives or partners in the field of green chemistry, offering a broad range of applications beyond just coloring textiles. Natural colorants not only provide aesthetically pleasing shades but also offer unique functional properties that are beneficial for the food and textile industries. These include antioxidant, insect repellent, deodorizing, antifeedant, antimicrobial, antifungal, fluorescence, and UV-protective effects [7-12]. The utilization of substantial quantities of water and auxiliary substances for dye extraction and subsequent dyeing procedures has raised significant apprehensions over the production of wastewater containing elevated concentrations of pollutants. The chemical composition of textile effluents from various textile laboratories and enterprises is very varied, resulting in detrimental effects on the aquatic ecosystems of various water bodies [13]. This factor forced scientists to consider alternate dyes and pigments that could be readily removed with little waste production.

This entails the use of cost-efficient cleaner manufacturing technologies and the incorporation of novel dye-producing flora and fauna derived from sustainable harvesting methods, which include various microorganisms, such as bacteria, fungi, algae, yeasts, and actinomycetes. Research investigations on the synthesis of pigments from microorganisms are in their nascent phase and need state-of-the-art research facilities to enhance the commercial feasibility of pigment manufacturing procedures and techniques. Bacterial farming has several benefits, including rapid and uncomplicated growing regardless of the season, high productivity, straightforward extraction, genetic alteration capabilities, and the ability to pick certain strains [14]. Yeasts, a kind of eukaryote, have some advantages over filamentous fungi. They exhibit faster growth rates but need cell disruption because of intracellular synthesis [15, 16]. Bacterial and fungal species from various groups create distinct secondary metabolites, including quinones, carotenoids, and anthocyanins, which are diverse types of colors [17]. The successful commercialization of carotenoid pigments from some distinct fungus species has garnered significant scientific interest in the textile industry [18]. Current research in textile coloring has made notable progress in developing pigments derived from Trichoderma sp. and Aspergillus sp. These pigments are utilized for dyeing cotton and silk, resulting in long-lasting color [19]. Several bacterial species that create various bio-pigments include Flavobacterium sp., A. aurantiacum, Micrococcus sp., P. aeruginosa, S. marcescens, Chromobacterium sp., and Rheinheimera sp. [15]. The first bio-pigment that was effectively grown and used for food purposes was ß-carotene, derived from the fungus Blakeslea. This pigment received approval from the European Union in 1995 to be used as a food additive. The production of this microbial pigment can readily meet the year-round demand in several areas of the food and textile industries [20]. Lichens have been used as a source of natural colors since prehistoric times. Paranoid lichens produce natural colors using the acetate-polymelonate pathway, which involves the biosynthesis of depsides and depsidones from phenolic rings [21]. The primary obstacle to producing anthocyanins on a large scale is the restricted availability of these compounds in plant tissues. A biosynthesis technique has arisen to address this disparity, using bacteria or yeast to produce natural chemicals on a huge scale in controlled environments. The use of second-generation lignocellulosic sugars may effectively meet the market demand for various pigments, hence enhancing the production of microbial pigments.

In this chapter, we provide current information on the extraction and chemical production of microbial pigments derived from various types of microorganisms including bacteria, cyanobacteria, fungi, algae, lichens, and others. This comprehensive study has also examined the techniques for enhancing the output of microbial pigment production by contemporary technologies, such as strain creation, co-substrate supplementation, and genetic engineering of bacteria. This also incorporates brief information about the uses of microbial pigments in different industries, such as pharmaceuticals, food, cosmetics, and textiles.

1.2 Classification of Microbial Pigments

1.2.1 Classification Based on the Source

Microbial pigments can be classified based on their source by categorizing them according to the microorganisms responsible for their production. This classification is based on the primary source of pigment production while certain pigments can be generated by more than one microbial source, such as bacteria, fungus, algae, etc. (Figure 1.1). In addition, the progress made in molecular techniques has resulted in the identification of new pigments derived from different microorganisms that were previously unexplored. This has broadened the range and intricacy of microbial pigments.

Figure 1.1 Classification of microbial pigments based on the type of microorganisms.

1.2.1.1 Bacterial Pigments

Researchers have shown significant interest in bacterial pigments due to their diverse industrial applications. These pigments have been extensively utilized in East and Southeast Asia across multiple sectors, including food, cosmetics, textiles, and pharmaceuticals. Bacteria demonstrate a remarkable ability to produce a wide array of natural compounds. Examples include carotenoids, bacteriochlorophylls, phenazines, quinones, melanins, flavins, monascins, violacein, prodigiosin, and indigo [22]. However, commercializing these pigments, especially for use in food or cosmetics, has encountered challenges due to the substantial investment required and the need for extensive toxicity evaluations. Technological advancements have significantly improved the extraction and large-scale commercialization of bacterial pigments, such as riboflavin, ß-carotene, and phycocyanin. There is also considerable potential for...