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Method Article
Here we present a protocol on adsorptive bioprocess to produce a biological product, especially a pigment that inhibits its own biosynthesis and inhibits the growth of the microorganism that produces it.
Melanins are natural pigments, and the presence of indole ring and numerous functional groups makes melanin an ideal choice for many applications such as UV protective agents, skincare, cosmetics etc. A marine Pseudomonas stutzeri produces melanin without the addition of tyrosine. The feedback inhibition was observed by melanin in the culture of a melanin-producing marine bacterium, Pseudomonas stutzeri. Melanin also demonstrated microbial growth inhibition. The Han-Levenspiel model-based analysis identified uncompetitive type product inhibition of melanin on the cell growth. Tyrosinase enzyme, which produces melanin, was inhibited by melanin. The double reciprocal plot of the enzymatic reaction in the presence of different melanin concentrations revealed uncompetitive product inhibition. An adsorbent-based adsorptive bioprocess was developed to reduce the feedback inhibition by melanin. Different adsorbents were screened to select the best adsorbent for melanin adsorption. Dosage amount and time were optimized to develop the adsorptive bioprocess, which resulted in an 8.8-fold enhancement in melanin production by the marine bacteria Pseudomonas stutzeri (153 mg/L to 1349 mg/L) without supplementation of tyrosine and yeast extract.
Melanins are polyphenol compounds whose monomeric unit is the indole ring. Melanins are responsible for most of the black, brown, and grey colorations of plants, animals, and microorganisms1. The most common melanins are eumelanins, which are dark brown or black pigments widely distributed in vertebrates and invertebrates2. Cephalopods, plants, and microbes are the major sources of melanin3. Melanin obtained from microorganisms has several advantages over melanin from cephalopods and plants. They are fast in growth and do not cause any problems of seasonal variations. Also, they modify themselves according to the growth medium and the operating conditions provided. Considering all these facts, the microbial sources are exploited as a major source of melanin with potential commercial applications4,5,6. Guo et al. used recombinant Streptomyces kathirae SC-1 to produce melanin up to 28.8 g/L in an optimized medium7. Lagunas-Muñoz et al. Obtained about 6 g/L of melanin in recombinant E. coli8. Wang et al. obtained about 4.2 g/L of soluble melanin after medium optimization9. Researchers also investigated marine cultures to produce melanin. Kiran et al. produced melanin from marine Pseudomonas species10. Kumar et al. isolated Pseudomonas stutzeri HMGM-7 from marine seaweed, which produced melanin in nutrient broth. All the reported melanin producers require medium supplements, yeast extract and/or peptone for melanin production, which may hinder the scale-up of the bioprocess. Raman et al. investigated melanin production from Aspergillus fumigatus AFGRD105, which did not require costly additives11.
A marine bacterium known as Pseudomonas stutzeri, isolated from seaweed, was selected for melanin production. This microorganism does not require additional supplementation of tyrosine and yeast extract for the production of soluble melanin and grows in seawater-based media, thereby reducing the potable water footprint and medium cost. Thaira et al. reported an optimized bioprocess using coconut cake meal for melanin nanopigment production using this marine bacterium in a previous publication12. The produced melanin was used for the highly efficient removal of heavy metals from the synthetic groundwater. However, during medium optimization, plausible feedback inhibition of melanin on the growth and product formation was identified. Therefore, in this protocol, feedback inhibition of melanin is investigated and quantified using the generalized Han-Levenspiel model. A simple and effective adsorptive bioprocess protocol is developed to reduce feedback inhibition to the maximum extent.
1. Growth and maintenance of Pseudomonas stutzeri culture.
2. Inhibition studies of melanin on the growth and enzyme activity
3. Modeling melanin inhibition kinetics
4. Development of the adsorptive bioprocess
5. Selection of the best adsorbent from different available adsorbents
6. Effect of dosage time of the adsorbent
7. Effect of amount of adsorbent dosage
8. Mathematical modeling of the bioprocess
9. Analytical techniques
Figure 1A,B demonstrates growth and melanin production under the influence of different initial melanin concentrations. The cell growth and melanin production decreased substantially with the increasing initial concentration of melanin. At 500 mg/L initial melanin concentration in the medium, the biomass and melanin reduced to almost 50% of the maximum value obtained in control. At 1000 mg/L of initial melanin concentration, there was marginal melanin production. The biomass...
Product inhibition is a major bottleneck in bioprocessing which leads to reduced productivity. Several methods exist to reduce product inhibition, such as continuous bioprocess and in situ product removal techniques. However, these options require a complete overhaul of the existing bioprocessing facility23,24,25,26,27,28<...
The authors do not have any conflict of interest
We thank the Department of Science and Technology (DST/TSG/WP/2014/58), India, and the National Institute of Technology Karnataka for providing funding for the development of the above protocol.
Name | Company | Catalog Number | Comments |
Alumina+A15A26A3:A13A3:A16A3:A17 | HiMedia | GRM1909 | |
Activated carbon | HiMedia | PCT1001 | |
Artificial Sea Water Medium | HiMedia | M1942 | |
Bradford reagent kit | HiMedia | ML106 | |
Celite | HiMedia | GRM226 | |
Centrifuge | REMI | CM-8 | |
Centrifuge tubes | HiMedia | PW1207 | |
Dinitrosalicylic acid | HiMedia | GRM1582 | |
Erlenmeyer flask | Borosil | 4980021 | |
fuller's earth | HiMedia | GRM232 | |
Glucose | HiMedia | MB037 | |
HCl | HiMedia | AS004 | |
L-tyrosine | HiMedia | RM069 | |
Microsoft Excel | Microsoft | ||
Nanoparticle analyzer | HORIBA Scientific | Nanopartica SZ-100 | |
Nutrient Agar medium | HiMedia | M001 | |
Petri plate | HiMedia | PW054 | |
Phosphate buffer | HiMedia | M1452 | |
Sodium hydroxide | HiMedia | MB095 | |
Spectrophotometer | Thermofisher | Genesys 10 | |
Stirred tank bioreactor | Scigenics | Bioferm LS | |
TE Buffer | HiMedia | ML060 | |
Transmission Electron Microscope | JEOL | JEM-2100 | |
Zeolite | HiMedia | GRM3834 |
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