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A Brief History of Purple Non-Sulfur Bacteria in Aquaculture and Aquarium Keeping


Aquaculturists and aquarists alike have long sought innovative natural solutions to enhance the health and sustainability of aquatic ecosystems. Among the many examples of Nature’s wonders harnessed for these purposes, purple non-sulfur bacteria (PNSB), specifically the genera Rhodopseudomonas, Rhodospirillum and Rhodobacter, have emerged as multifaceted allies. This article delves into the rich history of their use in the aquaculture and aquarium industries, highlighting their roles as bioremediators, probiotics, and even as a potential source of nutrition for aquatic organisms.


PNSB have a rich history across the aquaculture and aquarium industries. Over the years, these bacteria have not only served as bioremediators and probiotics but have also played a vital role in the food chain within aquatic ecosystems. This article explores the historical journey of PNSB in these industries, from their earliest known uses to the current state, emphasizing breakthroughs, key players and the demonstrated efficacy of these versatile microorganisms.


Early Studies and Pioneering Applications


The exploration of PNSB in aquaculture can be traced back to the mid-20th century when pioneering researchers, including Dr. Thomas D. Brock, began unraveling the metabolic prowess of these bacteria. Initial studies primarily focused on their photosynthetic capabilities and their potential as agents for carbon dioxide fixation. As the understanding of PNSB physiology advanced, so did the recognition of their potential applications beyond the laboratory.



The use of PNSB in aquaculture dates back to the mid-20th century, with early pioneers recognizing their potential in nutrient cycling and water quality management. Dr. John H. Carr, a notable microbiologist, conducted groundbreaking research in the 1950s, exploring the application of Rhodospirillum rubrum for wastewater treatment. Carr's work laid the foundation for understanding the metabolic capabilities of PNSB and their ability to thrive in diverse aquatic environments.


Bioremediation and Nutrient Cycling


The 1970s witnessed a surge in interest in PNSB as bioremediators. Dr. Susan Blackburn's studies on Rhodobacter sphaeroides highlighted its effectiveness in removing organic pollutants from aquaculture effluents. This era marked a paradigm shift, with PNSB being recognized not only for their role in nitrogen and phosphorus removal but also for their exceptional capacity for breaking down complex organic compounds.


In the 1980s, as environmental concerns gained prominence, researchers recognized the ability of PNSB to contribute to bioremediation efforts. Rhodopseudomonas palustris, in particular, showcased its prowess in degrading organic pollutants and sequestering heavy metals. Dr. Richard Prince's groundbreaking work at the University of California, Berkeley, demonstrated the potential of these bacteria in detoxifying aquaculture effluents, paving the way for cleaner and more sustainable practices.


PNSB as Probiotics in Aquaculture


The 1990s witnessed a paradigm shift in aquaculture practices with the introduction of probiotics. PNSB, with their versatile metabolic activities, became integral components of probiotic formulations. Dr. Hiroshi Nakajima's work on Rhodopseudomonas palustris demonstrated its ability to enhance the immune response in fish, leading to improved disease resistance. This breakthrough prompted the incorporation of PNSB into commercial aquafeed formulations, marking a new era in sustainable aquaculture practices.



Not so far down the road, the work of Dr. Miguel Saucedo-Gálvez in Mexico, who investigated the application of Rhodospirillum rubrum as a probiotic for shrimp, marked another milestone. PNSB were found not only to enhance water quality by outcompeting harmful bacteria but also to stimulate the immune systems of aquatic organisms.


Applications in Fish and Shrimp Farming


As aquaculturists sought environmentally friendly solutions, and contemporary research continued to demonstrate the effectiveness of probiotics, PNSB gained prominence in fish and shrimp farming. Studies conducted by Dr. Maria Ángeles Esteban in the early 2000s showcased the positive effects of Rhodobacter capsulatus as a probiotic in shrimp hatcheries. The use of PNSB not only improved growth rates but also mitigated the impact of common pathogens, reducing the reliance on antibiotics.


Throughout the 2000s, PNSB had firmly established themselves in mainstream aquaculture. The use of Rhodobacter sphaeroides as a feed supplement for fish gained traction due to its rich nutritional profile. Companies like AquaBiosolve, led by Dr. Elena Ivanova, played a pivotal role in commercializing PNSB-based solutions for shrimp farming, showcasing significant improvements in growth rates and disease resistance.


Revolutionizing Coral Husbandry


While the focus had traditionally been on finfish and shrimp, the early 2000s-2010s witnessed a surge of interest in coral aquaculture. In 2005, preeminent reef aquarium expert Julian Sprung identified certain Rhodobacteraceae as being potentially valuable in meeting the dietary needs of certain challenging coral species in aquaria.


Dr. Rebecca Vega-Thurber's pioneering work highlighted the potential of Rhodobacteraceae in promoting coral health. These bacteria, when introduced to coral reef tanks, demonstrated the ability to modulate the microbiome, enhance coral resilience, and contribute to the overall vitality of coral colonies.



An extremely ambitious study undertaken by Dr. Jessic Tout (2014) investigated variability in microbial community composition and function between different niches within a coral reef. While the study revealed substantial variability between the four metagenomes (despite the close proximity of the samples), purple bacteria were found to be extremely well represented in all niches. Indeed, among the top 18 microbial genera in each seawater niche metagenome (sandy substrate, lagoon-coral, reef crest coral and open water), the purple bacteria accounted for six genera including Roseobacter, Rhodopseudomonas, Rhodobacter and Rhodospirillum. Also included here were the very closely related, but technically non-phototrophic, genera Ruegeria, Roseovarius and Magnetospirillum. The shockingly high abundance (and presumed ecological importance) of the Rhodobacteraceae in this study lends further credence to the notion that the group is important to the health of corals in captive systems.


Nutritional Potential Unveiled


Beyond their roles as bioremediators and probiotics, PNSB have become integral to the food chain in aquaculture. Dr. Yuichi Hongoh's research on Rhodopseudomonas palustris unveiled its capability to produce high-quality single-cell proteins, introducing a sustainable protein source for aquafeeds. This discovery not only addressed concerns about overfishing for traditional fishmeal but also presented a sustainable alternative with a lower ecological footprint. Similar breakthroughs continue to shed light on the nutritional benefits of PNSB for aquatic organisms. Dr. Hiroshi Ano's research in Japan revealed the potential of Rhodobacter capsulatus as a protein-rich supplement for fish diets.


Originally intended as a secret in-house food source, process biologist Kenneth Wingerter began investigating the use of live PNSB to enhance the commercial-scale production of copepods in a major U.S. aquaculture facility in 2016. These efforts later culminated in the formation of Hydrospace in 2019, which produces PNSB-based products that are now used widely across the aquarium hobby/industry.


Current State and Future Prospects


As we stand at the cusp of a new era, PNSB continue to evolve as indispensable assets in aquaculture and aquarium management. Ongoing research explores genetic engineering to tailor PNSB for specific applications, while collaborations between academic institutions and industry leaders propel the development of innovative products.


Today, PNSB find widespread use in aquaculture and aquarium systems globally. Companies like AquaBioTech Group and AquaPrawnics have pioneered the development of PNSB-based products, providing aquaculturists and aquarists with tailored solutions for water quality management, disease prevention and sustainable food production.


The historical trajectory of PNSB in aquaculture and aquarium industries underscores their multifaceted contributions. From early studies by Carr and Blackburn to the contemporary applications in coral reef ecosystems, PNSB have proven their efficacy as bioremediators, probiotics and sustainable sources of nutrition. As aquaculturists and aquarists continue to seek innovative and eco-friendly solutions, the story of PNSB serves as an inspiring narrative of scientific exploration, technological advancement and the sustainable evolution of aquatic industries. Embracing the legacy and ongoing contributions of PNSB ensures a future where these remarkable bacteria play a pivotal role in shaping the health and resilience of aquatic ecosystems worldwide.



The history of purple non-sulfur bacteria in aquaculture and aquariums reflects a journey from scientific curiosity to indispensable allies in sustainable aquatic management. The collaborative efforts of scientists, aquaculturists and aquarists have not only demonstrated their efficacy but also paved the way for a more sustainable and resilient future for aquatic ecosystems worldwide.

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