PNS CryoPak™: Frozen Probiotics for Clean Aquatic Feeding

Frozen foods are a staple of serious aquarium husbandry. They are convenient, nutritionally dense, readily accepted by many animals, and particularly useful when feeding delicate fish, corals, filter-feeding invertebrates, larvae, or live-feed cultures. But most frozen aquarium foods provide nutrition alone. PNS CryoPak™ is a bit different: it delivers concentrated nutrition in the form of living, probiotic purple nonsulfur bacteria (PNSB).

PNS CryoPak is a professional-grade frozen PNSB formulation featuring Rhodopseudomonas palustris and Rhodobacter sphaeroides. It is produced from active cultures using a carefully controlled centrifugation process that concentrates the bacterial biomass while removing most of the spent culture liquid before freezing. The result is a compact, high-cell-density frozen product intended for aquariums, ponds, aquaculture systems, and live-feed production vessels.

This format addresses an important distinction that can easily be overlooked when working with microbial aquarium products: the desirable component of a PNSB culture is principally its living microbial biomass—not necessarily every milliliter of dirty liquid in which that biomass was grown.

By separating and concentrating that biomass, PNS CryoPak provides substantially more of what the aquarist wants while substantially reducing what the aquarist does not.

Why Purple Nonsulfur Bacteria?

Purple nonsulfur bacteria are an unusually versatile group of phototrophic microorganisms. Unlike algae and cyanobacteria, their photosynthesis is anoxygenic: they harvest light energy without splitting water and releasing oxygen. They also possess remarkable metabolic flexibility, allowing many PNSB to grow under widely differing environmental conditions and utilize numerous organic compounds.

That flexibility has attracted attention far beyond the aquarium hobby. PNSB have been studied for wastewater treatment, nutrient recovery, agriculture, sustainable protein production, bioremediation, and commercial aquaculture. A 2023 review specifically examining PNSB as aquaculture probiotics described genera including Rhodopseudomonas and Rhodobacter as established subjects of aquaculture research and noted their practical use as probiotics and water conditioners. Their usefulness in aquaculture is especially interesting because PNSB can occupy two roles simultaneously. They are microorganisms with potential probiotic effects, but they are also food.

That second point is important.

Research on purple phototrophic bacterial biomass has repeatedly demonstrated impressive nutritional characteristics. Depending upon species and cultivation conditions, PNSB biomass can contain roughly 40–60% or more protein on a dry-weight basis, with useful essential amino-acid profiles. PNSB biomass may additionally contain lipids, carotenoids, bacteriochlorophylls, vitamins and other biologically active cellular compounds. Consequently, when an aquatic animal consumes PNSB, it is not merely ingesting a bacterial inoculant. It is consuming tiny packages of microbial nutrition.

Two Proven PNSB, One Product

PNS CryoPak features a select blend centered on two extensively studied PNSB species: Rhodopseudomonas palustris and Rhodobacter sphaeroides.

R. palustris has a particularly interesting history in aquaculture research. In a controlled study involving juvenile Nile tilapia, researchers compared several probiotic bacteria added directly to culture water. Fish receiving R. palustris G06 exhibited significantly greater final weight, daily weight gain, and specific growth rate than untreated controls.

More recent research has broadened the picture. Dietary supplementation with R. palustris in sea urchins has been associated with improvements in growth, digestive enzyme activity, antioxidant capacity, nonspecific immunity, intestinal microbial diversity, and several measures of gonadal development and nutritional quality.

Other work involving Rhodopseudomonas and related purple bacteria has repeatedly reported improved shrimp growth performance and feed conversion, as well as increased tolerance to ammonia stress. Notably, both live and freeze-dried PNSB demonstrated inhibitory activity against Vibrio pathogens in vitro in one study.

Rhodobacter sphaeroides likewise has a substantial aquaculture research history. A study of white shrimp cultivation found strains of R. sphaeroides, in combination with other PNSB, useful as probiotics for controlling water quality and improving shrimp growth and survival under experimental conditions involving acute hepatopancreatic necrosis disease (AHPND). The pigments and other metabolites associated with Rhodobacter are interesting as well. For example, research with a carotenoid extract derived from R. sphaeroides found improvements in growth and nonspecific humoral immune responses in seawater red tilapia.

These findings should not be interpreted to mean that every PNSB strain will produce every reported benefit in every aquarium animal. Probiotic effects are inherently strain-, dose-, diet-, host-, and environment-dependent. But taken together, the research makes a compelling case for PNSB as something considerably more sophisticated than simply another bacterial water additive. Countless anectdotes within the aquarium hobby community--particularly over the last five years--serve to build this case.

Microfood, Probiotic, and Nutritional Supplement

The extremely small size of bacterial cells creates feeding possibilities quite different from conventional frozen foods. PNSB biomass can enter microbial and planktonic food webs at their smallest scales. Depending upon the feeding biology of the organism and system, bacterial biomass may be consumed directly, incorporated into aggregates and biofilms, or consumed indirectly after being captured by protozoans and other microorganisms.

This makes concentrated PNSB particularly attractive for aquarists maintaining systems in which microbial nutrition matters: reef aquariums, larval systems, zooplankton cultures, shrimp systems, filter-feeding communities, and other highly managed aquatic environments. PNSB are also intriguing as a feed enrichment ingredient. Rather than broadcasting the product into the water, a thawed portion of PNS CryoPak can be incorporated into prepared foods immediately before feeding. This places concentrated PNSB biomass directly onto or among food particles. It similarly may be gut loaded into live feeds.

The nutritional rationale is substantial. Research on purple phototrophic bacterial biomass has reported approximately 58% protein in some preparations (often considerably higher), together with a broad spectrum of amino acids and measurable carotenoids and bacteriochlorophyll. Other research describes PNSB biomass as containing high-quality protein along with vitamins including B-group vitamins, vitamin E, and CoQ10.

A 2025 feeding study provides an especially interesting example of where this research is heading. In guppies, dietary purple bacteria were associated with an 18% improvement in growth and a 32% improvement in reproduction; certain treatments also increased pigmentation brightness, while PNSB-fed fish showed substantially higher survival following an experimental Aeromonas hydrophila challenge.

Again, PNS CryoPak should not be assumed to reproduce the results of a different strain or experimental diet. But such studies demonstrate why PNSB are increasingly being investigated not merely as bulk microbial protein, but as multifunctional aquafeed ingredients.

Why Concentrate the Culture?

This is where PNS CryoPak departs most significantly from conventional bottled PNSB products.

Growing microorganisms requires a culture medium containing water and nutrients. During cultivation, bacteria consume much of those nutrients and transform them into cellular biomass. But the finished culture liquid can still contain dissolved and suspended residual materials: unused nutrients, metabolic products, organic compounds, nitrogenous substances, phosphorus-containing compounds, salts, and other constituents of the growth medium. Some of these can contribute to the growth of unwanted bacteria or algae. Some are toxic or irritating to sensitive aquarium species. Some stink to high hell.

In a conventional whole-culture product, the consumer receives both the organisms and the culture liquid. That is not necessarily problematic when dosing small quantities of a well-formulated product. But if the goal is to deliver large numbers of PNSB cells as food, the accompanying liquid becomes increasingly unnecessary. In live feed vessels, that little bit of extra water volume can exceed the vessel's capacity, such as in a brine shrimp hatching cone. Worse, every additional volume of culture broth introduced to an aquarium represents material that the aquarium's biological filtration ultimately has to process.

PNS CryoPak approaches the problem differently. After cultivation, the culture is centrifuged. Centrifugal force separates much of the dense bacterial biomass from the surrounding liquid. Most of that liquid can then be removed, while the valuable cell fraction is retained and packaged. The concept is simple: keep the bacteria; leave much of their wastewater behind.

Less Wastewater Means Less Pollution Load

The environmental logic behind this process is supported by the very reason PNSB are so extensively studied for wastewater treatment: they are remarkably good at assimilating dissolved organic carbon and nutrients into biomass.

PNSB-based wastewater technologies have been investigated specifically for removal and recovery of organic matter, nitrogen, and phosphorus. Recent work with purple phototrophic bacteria treating saline seafood wastewater, for example, reported removal efficiencies reaching 88% for organic carbon, 75.5% for nitrogen, and 82.3% for phosphorus—with a substantial portion of those resources recovered as useful microbial biomass.

That provides a useful way to understand a mature PNSB culture. Nutrients have been transferred from the growth medium into bacterial cells, but the liquid phase does not magically become chemically empty. Some dissolved nutrients and organic compounds remain.

When the objective is aquarium feeding, adding that residual liquid along with every dose is inefficient. Dissolved organic compounds can contribute to biological oxygen demand and heterotrophic microbial activity. Nitrogen and phosphorus compounds ultimately join the aquarium's nutrient budget. Under unfavorable circumstances, excessive organic loading can contribute to cloudiness, biofilms, oxygen demand, nuisance microbial growth, and elevated dissolved nutrients.

Centrifugation does not make the bacterial biomass nutrient-free—the biomass is supposed to be nutrient-rich. Instead, it changes where the nutrient load resides. PNS CryoPak preferentially retains nutrients packaged inside the cells while reducing the amount carried as residual culture water. For a feeding product, that is a meaningful distinction--four little sticks are capable treating up to 16,000 gallons of aquarium water!

Less Culture Liquid, Less Odor

Concentrating the cells also provides a very practical quality-of-life benefit: reduced odor.

PNSB cultures can have a distinctive smell. Indeed, the scientific literature specifically notes that Rhodopseudomonas and Rhodobacter cultures can produce an unpleasant characteristic odor.

Much of what a person perceives as the odor of a microbial culture originates not simply from the intact cells, but from volatile and dissolved compounds in the surrounding culture broth and from microbial metabolites accumulating during growth. Removing a large proportion of that liquid therefore removes a large proportion of the reservoir capable of carrying those compounds.

PNS CryoPak is not intended to make living microbial biomass smell like nothing. Rather, concentrating the organisms and discarding excess culture liquid means that far less spent culture medium accompanies a given quantity of useful PNSB biomass. For home aquarists—and particularly anyone whose aquarium shares living space with other humans—that is no small advantage. For aquarium service providers or public aquarists who often feed while clients or visitors are present, this reduced release of odor is a real game-changer.

Why Freeze It?

Bottled PNSB products have an important advantage: Convenience at room or refrigerated storage temperatures, depending upon the formulation. PNS CryoPak is designed for a different objective. Freezing makes it possible to hold a dense, living concentrate in a relatively stable physical state without requiring the product to remain as a dilute liquid suspension.

The critical question, of course, is whether the organisms survive.

Internal viability testing of the strains used in PNS CryoPak was performed fllowing centrifugation and freezing. Both strains were found to remain highly viable following these processing steps. Thus, the product is not simply frozen bacterial biomass marketed on the assumption that some cells probably survive. The manufacturing concept was specifically evaluated to verify that its two defining processing steps—concentration and freezing—preserve high viability.

An “Ice Pop” Designed for Practical Dosing

PNS CryoPak is intended to occupy a useful middle ground between frozen food and probiotic culture: A frozen microbial food containing highly viable PNSB. Thus, proper handling remains important. Excessive heating can damage cells, and repeated freeze-thaw cycles can progressively compromise biological materials. The package should therefore remain frozen until needed. Do not microwave this product or expose it to excessive heat, and avoid unnecessary freeze-thaw cycles.

A microbial concentrate is only useful if it can be dispensed conveniently. PNS CryoPak therefore uses a distinctive elongated frozen “ice pop” format that is easy to store and portion. The including cutting board allows for better human and aquarium biosecurity--keeping this and other frozen foods in the fish room, and your favorite veggie chopping block in the kitchen. For broadcast feeding, simply remove the desired frozen portion and add it directly to the aquarium, pond, or culture vessel. The suggested maximum dosage is 12.5 mL per 40 gallons per day, with approximately one inch of the frozen pop treating 40 gallons.

For dietary supplementation, thaw the desired portion gradually under refrigeration or in cool water immediately before use, then mix it with dry food or previously thawed frozen food. Simple as that!

Who is PNS CryoPak for?

PNS CryoPak is likely to be especially useful to aquarists and aquaculturists who want to deliver large quantities of fresh PNSB biomass without simultaneously dosing large quantities of culture liquid. That includes:

• Reef keepers interested in wholistic, microbial-scale nutrition

• Breeders raising larval or juvenile fish and invertebrates

• Shrimp keepers

• Aquaculture operators

• Coral and ornamental aquaculture facilities

• Anyone maintaining rotifers, copepods, Artemia, or other live-feed cultures

It may be particularly attractive to advanced hobbyists who already use frozen feeds daily and would like to incorporate live microbial nutrition without adding another bottle-and-cap dosing routine.

High-density systems are another logical application. When nutrient management matters, minimizing unnecessary dissolved organic and nutrient inputs becomes increasingly valuable. A concentrated product makes it possible to distinguish between feeding microbial biomass and pouring microbial culture broth into the system.

And for users who already appreciate conventional PNSB products but wish they could administer dramatically more cells in dramatically less volume, CryoPak offers an entirely different, and arguably superior, delivery format.

More of What You Want—Less of What You Don't

PNS CryoPak is based on a straightforward idea: If PNSB themselves are the valuable nutritional and probiotic component of a culture, concentrate them.

Centrifugation removes much of the residual culture water. Freezing preserves the concentrated biomass in

a compact format. Viability testing confirms that both selected strains remain highly viable following concentration and freezing. The resulting frozen “ice pop” is easy to portion, broadcast into the water, incorporate into prepared diets, and store long-term.

At the same time, PNSB science continues to reveal why these organisms are so interesting in the first place. They are protein-rich microbial biomass. They contain valuable amino acids, pigments, and other bioactive compounds. Research across fish, shrimp, sea urchins, and other aquaculture applications has reported effects involving growth, feed utilization, immunity, stress tolerance, intestinal health, pathogen interactions, and water quality.

Of course, no single aquarium product replaces good nutrition, sensible stocking, filtration, water changes, or sound husbandry. Nor should results from individual aquaculture studies be treated as guarantees across species and systems. What abundant research does demonstrate, however, is that purple nonsulfur bacteria occupy an unusual and promising intersection between microbial ecology, probiotic supplementation, and nutrition.

PNS CryoPak makes that biology available in a new form:

• Fresh and concentrated

• Living and highly viable

• Nutritionally valuable

• Less residual wastewater

• Less odor

And perhaps most importantly, instead of shipping mostly water, PNS CryoPak concentrates the part that matters most—the PNSB themselves.

Selected References

Miyasaka, H., Koga, A., & Maki, T. (2023). Recent progress in the use of purple non-sulfur bacteria as probiotics in aquaculture. World Journal of Microbiology and Biotechnology, 39, 145. DOI: 10.1007/s11274-023-03592-6.

Zhou, X. et al. (2009). Effect of treatment with probiotics as water additives on tilapia (Oreochromis niloticus) growth performance and immune response.

Chumpol, S. et al. (2017). The roles of probiotic purple nonsulfur bacteria to control water quality and prevent acute hepatopancreatic necrosis disease (AHPND) for enhancement growth with higher survival in white shrimp (Litopenaeus vannamei) during cultivation. Aquaculture, 473, 327–336.

Delamare-Deboutteville, J. et al. (2019). Mixed culture purple phototrophic bacteria is an effective fishmeal replacement in aquaculture.

Alloul, A. et al. (2021). Purple bacteria as added-value protein ingredient in shrimp feed: Penaeus vannamei growth performance, and tolerance against Vibrio and ammonia stress. Aquaculture, 530, 735788.

Lu, H. et al. (2021). Purple non-sulfur bacteria technology: a promising and potential approach for wastewater treatment and bioresources recovery. World Journal of Microbiology and Biotechnology, 37, 161.

González Cámara, S. J. et al. (2025). Purple bacteria as sustainable nutraceutical ingredient in aquafeed: The case of guppies. Animal Feed Science and Technology, 326, 116394.