Over the last five years, we’ve exhaustively researched the use of purple nonsulfur bacteria (PNSB) in aquacultural applications. This intensive effort has served to 1) position Hydrospace as the foremost source of information about PNSB for aquarium hobbyists, and 2) guide the development of our flagship product, PNS ProBio™.
Born to reef
PNS ProBio™ is a premium, small-batch formulation of PNSB, made specifically for the home aquarist, that is matched by no other. It’s exceptionally clean. It’s exceptionally dense. It’s highly viable. It’s cultured under special conditions to promote the production of certain energy-reserving polymers that enhance viability as well as shelf stability.
And, perhaps best of all, it contains each of the Big 3 PNSB for aquatic use: Rhodopseudomonas palustris, Rhodospirillum rubrum and Rhodobacter sphaeroides. While the efficacy of various mixed-strain purple bacteria-based feed supplements and bioremediators has been demonstrated thoroughly (1, 2, 3, 4, 5, 6, 7, 8), these three species arguably have emerged as the most favored for use in professional aquaculture facilities worldwide.
So, how exactly do PNSB improve aquatic environments, and what is the purpose of including all of the Big 3 in tandem? Let’s start by briefly describing PNSB ecology. Like all purple bacteria, PNSB are quite similar to their extremely archaic ancestors. They’re regarded by biologists to be among the most metabolically versatile organisms on Earth:
They may utilize both organic and inorganic carbon (such as CO2) for growth (9).
They may obtain energy either through photosynthesis, but nevertheless can thrive in total darkness as strict heterotrophs (10).
They are predominantly euryhaline and so can move between freshwater, brackish and marine environments (11, 12, 13).
While they convert N2 gas into NH4 (i.e., nitrogen fixation), thereby generating a biologically available form of N for plants and algae (including zooxanthellae) (14), some PNSB are additionally capable of converting NO3 into N2 (i.e., denitrification)(15).
They survive within the guts of wild and captive fish, crustaceans and corals (16, 17, 18, 19, 20) where they not only act as probiotics, but also promote the growth of certain other probiotics (21).
One polyculture, many uses
PNSB are (despite their impressive adaptability) most often observed in a rather marginal habit: Moderately illuminated, poorly oxygenated pockets or layers in the substrate that are rich in organic matter. Though each of the Big 3 species is more or less restricted to this type of environment, each has its own unique survival strategy. A few examples of such differences include:
Each of the three is armed with its own unique array of pathogen-inhibiting antimicrobial and antibiotic compounds (some of which grant probiotic effects for host organisms) (22).
Each has a unique carotenoid profile, collectively maximizing their nutritional value as a live feed (23).
While Rhodobacter is a strong biofilm builder, effectively competing against less desirable benthic microbes such as red cyanobacteria, Rhodospirillum is a strong swimmer, presenting ample grazing opportunity for bacterioplanktivores such as corals, bivalve mollusks, larval copepods, etc.
Rhodopseudomonas is unique among the three in its ability to perform denitrification (24).
Thus, while the three PNSB in PNS ProBio™ share numerous benefits for aquatic plants and animals, and none of these (or any PNSB) are known to be pathogenic (25), each also exhibits its own distinctive capabilities. The result is a highly effective consortium with a functional impact that is greater than the sum of its parts!
Gently shake the bottle before each use. As with any other live microfeed, cutting UV sterilizers, ozone generators and protein skimmers for one hour after each feeding is advised.
Special applications
Direct transfer of PNS ProBio™ to dry rock and porous biomedia can promote colonization. This is accomplished simply by soaking product into the material under anaerobic conditions (i.e., no aeration). Place the rock/media in a clean, sealable container that is just large enough to contain the material. Add to the container a sufficient volume of PNS ProBio™ to thoroughly soak the material. Place lid on the container and allow material to condition for 24 hours. After the conditioning period, add the material (along with the cultures) directly to the tank, filter system, etc.
PNS ProBio™ may be gut loaded into live feeds such as rotifers, copepods, adult brine shrimp, etc. While optimal dosage and loading time will depend upon numerous factors such as type/density of food items, we recommend a starting point of 4 mL/gal (holding vessel volume) for approximately 30 min. Product is best applied after the food items are strained and rinsed. Maintain adequate aeration throughout the entire loading period.
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