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Duel of the Microbes: Rhodospirillum rubrum vs Rhodopseudomonas palustris

All microbes are not nearly created equal. Each phylum, class, family, genus, species, strain and cell is imparted with a particular genetic potential. This unique array of genetic information manifests as a metabolic arsenal, one which allows the microbe to derive energy from its environment, persist and continue its genetic lineage. The amalgamation of millions of microbe varieties and their persistence drives the chaotic symphony of life. Simply put, microbes destabilize their environment to survive, yet it is their collective destabilization which detoxifies ammonia and nitrite, converts nitrate into harmless nitrogen gas, solubilizes phosphates and creates our glorious oxygen-rich atmosphere! The world of microbes is defined by competition and supremacy of the fit, but the existence of higher organisms (corals, fish, insects, plants, mammals etc.) is a testament to the reality that collective symbiosis is the most powerful of life’s attributes. Though there are plenty of destructively opportunistic or even pathogenic microbes,the broad majority of microbes perform some base environmental service which fosters the prosperity of other forms of life. However, it cannot be overstated that not all microbes are created equal:


Some are slackers.

Some are salarymen.

Some are superheros.


That is the mission of Hydrospace: to recon, recruit and refine the world’s most powerful

microbes and utilize them to maximize the health/growth of waters and soils! The purple non-sulfur bacteria (PNS) represent the vanguard of Hydrospace’s growing library of powerful

probiotics: Rhodospirillum rubrum and Rhodopseudomonas palustris. But what distinguishes

these two microbes? And what qualities make them so beneficial to rose gardeners, cannabis cultivators, shrimp/fish farmers and reef aquarists alike? Both Rhodospirillum rubrum and Rhodopseudomonas palustris are members of the gram-negative Proteobacter phylum. This was declared “the phylum of the purple bacteria and their relatives” by the microbiologist Carl Woese in 1987. Proteobacter is divided up into a growing number of Classes: Alphaproteobacter, Betaproteobacter, Gammaproteobacter, Epsilonproteoacter, Zetaproteobacter, Oligoflexia, Acidithiobacillia and Hydrogenphalialia. It is the Class Alphaproteobacter which contains dozens of commercially important probiotic species.


So then what is the difference between Rhodopseudomonas and Rhodospirillum?

The Nitrobacteracae (some now use Bradyrhizobiaceae) is a family which contains the nitrogen-fixing Bradyrhizobium, the nitrite-oxidizing Nitrobacter and of course, the purple non-sulfur bacteria Rhodopseudomonas. Rhodopseudomonas palustris possesses a ‘swiss army knife’ metabolism in which it is able to switch between metabolic pathways depending on the environmental conditions presented. For example, R. palustris is more than capable of biofiltration (i.e converting ammonia to nitrite, nitrite to nitrate) under anaerobic conditions. But whereas conventional biofilter species cannot occupy anaerobic substrates, R. palustris can while performing a different array of metabolic functions. Under anaerobic conditions, R. palustris can perform denitrification, where nitrate is removed as inert nitrogen gas. This species can also perform diazotrophy to fix atmospheric nitrogen into ammonia in oligotrophic environments.


Rhodopseudomonas palustris is also a photosynthetic powerhouse capable of consuming excess carbon dioxide, nitrate and phosphate. R. palustris converts all of this excess waste into proteins, lipids and other valuable nutritional compounds. The carotenoids and other pigments utilized by R. palustris for photosynthesis and photoprotection, act as incredible antioxidants/oxygen transporters when consumed by livestock and humans. In addition, R. palustris has been observed amongst the gut flora of species such as carp, cows and penaeid shrimps. There is mounting evidence that established gastrointestinal R. palustris facilitates digestion of food and secretes immunostimulating substances. R. palustris is also a potent photosynthetic symbiont of plants and corals through the sequestration of

atmospheric nitrogen, solubilization of phosphates and release of localized phytohormones. The R. palustris in Hydrospace PNS ProBio™ is cultivated in an organic carbon media. This media is a freshwater tea of the Eurasian watermilfoil (Myriophyllum spicatum) and is rich in cellulose, tannins, polyphenols and other difficult carbon forage. This 'trains' PNS ProBio to feast on the detritus, plant debris and uneaten feed which inevitably accumulates in any production system. Because of its extreme metabolic plasticity, R. palustris can release and absorb nitrogen/phosphorus into the surrounding environment as needed by the plants/animals associated with it. PNS ProBio sets itself apart by enhancing the functionality and long-term stability of already established systems; whether they be terrestrial (i.e. moist soil), freshwater, brackish or marine.


The Rhodospirillaceae is another incredibly diverse family but contains mostly aquatic genera with an assorted range of biofiltration capacities. Rhodospirillum rubrum is a gram-negative pink bacterium which can also operate under aerobic and anaerobic conditions. This species does not conduct photosynthesis under aerobic conditions. Under anaerobic conditions, Rhodospirillum rubrum produces a wide range of novel pigments such as bacteriochlorophylls and carotenoids, though not the same exact array as Rhodopseudomonas palustris. This species is also capable of diazotrophy and is associated with the gut microbiome, plant rhizosphere and is a holobiont of many terrestrial animals, plants and photosynthetic corals. Because of its ability to detoxify selenium and other heavy metals, Rhodospirillum rubrum is associated with hydrothermal vent species and has much potential in wastewater remediation. The R. rubrum in Hydrospace PNS Substrate Sauce™ is cultivated in a saltwater medium. This makes it more appropriate for direct application in reef aquariums, commercial mariculture and mangrove propagation. However R. rubrum will gradually adapt to freshwater and terrestrial systems. PNS Substrate Sauce is cultivated in an inorganic nitrogen (ammonia) media. It also contains supplemental phosphates to fuel the growth of other beneficial microbes. This makes it appropriate for dosing into new, ‘naive’ systems which require aggressive ammonia/nitrite cycling.


Should I seed my system with Rhodopseudomonas or Rhodospirillum?


Seed Both. Biodiversity is Power.


The answer to that question is multiplicity of metabolic function. Although chemical processes are generalized under the titles of ‘diazotrophy’ and ‘denitrification’, these are terms of relative convenience and fail to describe the overwhelming diversity of the reactions they describe. For example, denitrification depends on the enzyme nitrogenase. However enzymes are tools and multiple forms can perform the same function. Classically, it was understood that molybdenum was the important central base of nitrogenases--until vanadium based nitrogenases were discovered…and iron nitrogenases. Betancourt et al 2000 isolated/observed dominant populations of vanadium-nitrogenase bearing R. rubrum in mangroves swamp soils which were deficient in molybdenum. This demonstrates how MANY different enzyme and metabolic pathway combinations can result in the same ecological service be it removing ammonia, solubilizing phosphates or photosynthesizing. It is within these devilish details that microbial diversity reveals its true power.


Multiplicity of Metabolic Function is core to the long term stability of any ecological system be it a rose garden, a reef aquarium, a shrimp tank or a koi pond. The overall concept is that

multiple different microbes exist on the same general resource. Different microbes partition

resources so no single species is completely responsible for the biochemical service. If conditions change and the dominant species is depleted, there is a greater chance that other species/strains will possess the genetic tools to adapt. This is because like

Rhodopseudomonas palustris and Rhodospirillum rubrum, no two microbes photosynthesize the same, nor consume ammonia the same, nor fight Vibrio spp. the same, nor colonize animals/plants/corals the same. Diversity is strength, powerful diversity is infinite strength. Good growing soil, coral reefs, productive shrimp ponds: these things are all united by the collective functioning of competing microbes working towards greater biological synchrony. PNS ProBio and PNS Substrate Sauce are but the two vanguards of Hydrospace’s Greater Microbial Movement. Our mission: Build new ecosystems with nature’s elite bacteria. After all:


“It’s the little things that rule the world”


--E.O. Wilson


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