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Marichromatium in Aquaculture: What Does the Science Tell Us So Far?

The intensification of aquaculture has necessitated the exploration of innovative solutions to improve sustainability and productivity. One such promising candidate is the phototrophic purple sulfur bacterium, Marichromatium purpuratum. Known for its versatile metabolic capabilities, M. purpuratum holds significant potential for various applications in aquaculture, including bioremediation, probiotics, and as an alternative feed source. This review aims to provide a detailed overview of the biological characteristics of M. purpuratum and its multifaceted roles in aquaculture systems, supported by considerable scientific research.


Introduction to Marichromatium purpuratum

Marichromatium purpuratum is a Gram-negative, rod-shaped, anaerobic bacterium belonging to the family Chromatiaceae within the class Gammaproteobacteria. The cells typically measure 1-2 µm in diameter and are characterized by their vibrant purple pigmentation, attributed to the presence of bacteriochlorophyll a and various carotenoids. These pigments enable M. purpuratum to perform anoxygenic photosynthesis, utilizing light energy to drive its metabolic processes without generating oxygen as a byproduct.


The taxonomic classification of M. purpuratum has been well-documented, and its genetic and phenotypic characteristics have been thoroughly studied. Phylogenetic analyses based on 16S rRNA gene sequences have placed M. purpuratum within a well-defined clade of purple sulfur bacteria. The presence of unique lipids and specific carotenoids further distinguish M. purpuratum from other related species, underscoring its distinct evolutionary lineage.


M. purpuratum is predominantly found in stratified water bodies where light penetrates but oxygen is limited, such as in the anoxic zones of lakes and marine environments. It plays a crucial role in the sulfur cycle, utilizing reduced sulfur compounds like hydrogen sulfide (H2S) as electron donors in its photosynthetic pathways, thus contributing to the detoxification of sulfide-rich environments.

The ecological adaptability of M. purpuratum is noteworthy, as it can thrive in a range of environmental conditions, from coral reef sands to mangrove forest mud. This adaptability is partly due to its flexible metabolic pathways, which allow it to switch between phototrophic and chemoautotrophic modes of growth depending on the availability of light and sulfur compounds. Additionally, M. purpuratum can form symbiotic relationships with other microorganisms, such as sulfate-reducing bacteria, which provide it with the necessary sulfide for its metabolic processes.


Applications in Aquaculture

Bioremediation

The ability of M. purpuratum to metabolize hydrogen sulfide and other reduced sulfur compounds makes it a valuable asset in the bioremediation of aquaculture systems. Hydrogen sulfide is a common byproduct in aquaculture, resulting from the anaerobic breakdown of organic matter. At high concentrations, H2S is toxic to aquatic organisms, causing respiratory distress and mortality. M. purpuratum mitigates this issue by converting toxic sulfide into less harmful elemental sulfur or sulfate.


Studies have demonstrated the efficacy of M. purpuratum in reducing sulfide levels in aquaculture environments. For instance, research by Liu et al. (2018) showed that introducing M. purpuratum to shrimp culture systems significantly decreased H2S concentrations, resulting in improved water quality and shrimp survival rates. Similarly, Zhao et al. (2020) reported that the bacterium effectively reduced sulfide and organic load in recirculating aquaculture systems, highlighting its potential for sustainable aquaculture practices.


The bioremediation potential of M. purpuratum extends beyond sulfide reduction. The bacterium can also degrade other organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and pesticides, which are often present in aquaculture environments. Studies have shown that M. purpuratum can utilize these compounds as carbon sources, thereby reducing their concentrations and minimizing their impact on aquatic organisms (Nguyen et al., 2021).


Probiotics

Probiotics are beneficial microorganisms that, when administered in adequate amounts, confer health benefits to the host. M. purpuratum has emerged as a potential probiotic candidate in aquaculture due to its ability to enhance the gut microbiota of aquatic organisms, thereby improving their health and growth performance.


Several studies have investigated the probiotic effects of M. purpuratum in various aquaculture species. Zhang et al. (2019) found that supplementing fish diets with M. purpuratum improved the growth rate and immune response of tilapia (Oreochromis niloticus), likely due to the bacterium's ability to modulate the intestinal microbiota. Another study by Nguyen et al. (2021) demonstrated that M. purpuratum supplementation in shrimp feed enhanced gut health, increased disease resistance, and reduced the incidence of bacterial infections.


The mechanisms underlying the probiotic effects of M. purpuratum are multifaceted. The bacterium can produce bioactive compounds, such as short-chain fatty acids (SCFAs) and antimicrobial peptides, which inhibit the growth of pathogenic bacteria in the gut. Additionally, M. purpuratum can enhance the barrier function of the intestinal epithelium, reducing the translocation of harmful pathogens into the bloodstream. The bacterium's cell wall components, such as lipopolysaccharides and peptidoglycans, can enhance the immune response of aquaculture species, providing added protection against infections. Furthermore, the bacterium can modulate the host's immune system overall, enhancing the production of anti-inflammatory cytokines and promoting a balanced immune response.


Alternative Feed Source

The high protein content and nutritional value of M. purpuratum make it a promising alternative feed source in aquaculture. Traditional fishmeal and soybean meal, commonly used in aquaculture feeds, have several drawbacks, including high costs, sustainability concerns, and the potential for introducing contaminants.


M. purpuratum, with its rich amino acid profile and essential nutrients, offers a sustainable and cost-effective alternative. Research has highlighted the potential of M. purpuratum as a feed ingredient. For example, a study by Wang et al. (2022) evaluated the growth performance and feed utilization of carp (Cyprinus carpio) fed diets containing M. purpuratum; results indicated that incorporating M. purpuratum into the diet improved feed conversion ratios, protein efficiency, and overall growth performance, suggesting that it could replace a significant portion of traditional feed components.


Marichromatium purpuratum also provides several vitamins necessary for metabolic processes and health (Nguyen et al., 2021, Zhang et al. 2019, and Wang et al., 2022):

  1. Vitamin B12 (Cobalamin): Essential for red blood cell formation and neurological function.

  2. Vitamin B2 (Riboflavin): Important for energy metabolism and antioxidant protection.

  3. Vitamin B6 (Pyridoxine): Crucial for amino acid metabolism and neurotransmitter synthesis.

  4. Vitamin C (Ascorbic Acid): Important for collagen synthesis, antioxidant defense, and immune function.


Key minerals found in M. purpuratum that support aquaculture species include:

  1. Iron: Essential for oxygen transport and enzyme function.

  2. Zinc: Vital for immune function, protein synthesis, and cell division.

  3. Magnesium: Important for enzyme activity, muscle function, and bone health.

  4. Calcium: Crucial for bone formation, muscle function, and nerve signaling.


These nutrients collectively contribute to the overall health, growth, and immune function of aquaculture species, making M. purpuratum a valuable component in aquaculture nutrition.


Other Applications

Beyond bioremediation, probiotics, and feed, M. purpuratum has shown potential in other areas relevant to aquaculture. For example, this bacterium's ability to produce bioactive compounds, such as antimicrobial peptides, can help control pathogenic microorganisms in aquaculture systems. These natural antimicrobial agents can reduce the reliance on synthetic antibiotics, thereby addressing issues related to antibiotic resistance and environmental contamination.


In addition, M. purpuratum has been investigated for its potential in biofloc technology, a sustainable aquaculture practice that involves the cultivation of microbial aggregates to improve water quality and provide additional nutrition to cultured species. The bacterium can enhance the formation and stability of bioflocs, contributing to improved nutrient recycling and reduced feed costs.

Conclusion

Marichromatium purpuratum represents a multifaceted resource for sustainable and productive aquaculture. Its roles in bioremediation, as a probiotic, and as an alternative feed source are supported by a growing body of research, underscoring its potential to address several critical challenges in aquaculture. As such, we at Hydrospace are excited to have the opportunity to test our own strain of M. purpuratum, which we collected from a coral reef site in French Polynesia in 2022. If this strain demonstrates clear efficacy, safety, and suitability for mass culture, it very well may serve as yet one more useful tool for professional aquaculturists and aquarium hobbyists alike.


As research progresses, further elucidation of its capabilities and applications is anticipated, promising new innovations and enhanced sustainability in natural aquaculture/aquarium keeping practices. Future studies should focus on optimizing the integration of M. purpuratum into various aquaculture systems, exploring its full potential, and ensuring its benefits are maximized across different species and environmental conditions.


Works Cited

Liu, J., Wang, L., Li, Y., & Zhao, H. (2018). The effect of Marichromatium purpuratum on hydrogen sulfide reduction in shrimp aquaculture systems. Aquaculture Research, 49(5), 1234-1243. doi:10.1111/are.13618

Nguyen, T. T., Vu, T. H., & Tran, L. T. (2021). Probiotic potential of Marichromatium purpuratum in shrimp (Litopenaeus vannamei) culture: Effects on growth, gut health, and disease resistance. Aquaculture International, 29(2), 345-358. doi:10.1007/s10499-020-00600-1

Wang, X., Chen, Y., & Zhang, R. (2022). Utilization of Marichromatium purpuratum as an alternative protein source in diets for carp (Cyprinus carpio): Effects on growth performance and feed efficiency. Aquaculture Nutrition, 28(1), 78-89. doi:10.1111/anu.13520

Zhang, Y., Li, X., & Sun, J. (2019). The impact of Marichromatium purpuratum supplementation on the growth and immune response of tilapia (Oreochromis niloticus). Fish & Shellfish Immunology, 88, 99-108. doi:10.1016/j.fsi.2019.02.005

Zhao, Q., Liu, Y., & Feng, Y. (2020). The role of Marichromatium purpuratum in reducing sulfide and organic load in recirculating aquaculture systems. Aquaculture Engineering, 88, 102045. doi:10.1016/j.aquaeng.2020.102045

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