Kenneth Wingerter
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There are a lot of things that can and should be said here. You are likely referring to Dr. Hovanec’s comments from the September 9 ReefBum episode (around 16:34/32:30). He says “Just because you throw the bacteria in there doesn’t mean that there’s a niche for them–-a place that they can live.”
This is true for PNSB as it is for all types of bacteria. Hence why we provide a dark, highly aerobic habitat when attempting to promote the growth of nitrifying bacteria. We posit that providing an illuminated, anaerobic habitat can similarly promote (if not guarantee) the establishment of persistent PNSB populations. However, as with nitrifiers and any microbial group, we cannot predict with any certainty the size of a PNSB population that will arise in a given aquarium due to the uniqueness of each system; this depends entirely upon many, many factors such as nutrient availability, organic carbon availability, lighting characteristics, substrate composition, water flow characteristics, temperature, pH, levels of bactivory, presence of bacterioviruses and especially the abundance/composition of competing microbial groups. As Tim alludes to in his following reference to Aquabiomics, it appears that ecologically important genera such as Rhodopseudomonas and Rhodospirillum indeed succumb to competitive exclusion in captive systems (and/or they tend to die off en rout from the natural habitat). To the point, our aquaria differ markedly from natural reefs physicochemically; this leads to very different microbiomes. Tim may himself be alluding to similar observations I described during my interview on Reefstock@Home Episode 5 (22:25-1:24:46 through 24:53-1:24:46). These differences in microbial communities are almost certainly not without negative consequences where the health of our corals is concerned.
Tim doesn’t at all seem to imply here that it’s pointless to add PNSB just because they may not persist indefinitely. In fact, he immediately goes on to make the point that some of his own products (which we can assume he considers to be useful) must be replenished for continued utility (ReefBum, from 17:00-32:30 until the technical difficulty occurs).
The reasons to add PNSB to a reef tank are pretty compelling to me:
- They are shown to be extremely abundant on healthy natural reefs.
- Corals are demonstrated to form unusually close symbiotic relationships with certain PNSB genera (e.g. Rhodopseudomonas).
- These microbes are important competitors of sometimes harmful genera (most notably Vibrio).
- They may be outcompeted in the unnatural environment of an aquarium system.
- Their numbers can however be boosted through the use of live, concentrated, bottled cultures.
- Dosing (and, if necessary, re-dosing) PNSB replenishes an important coral food source/symbiont and serves as a “re-set button” for the resident microbial community.
I can understand why aquarists would seek to “seed” PNSB, much in same way as they do nitrifying bacteria, copepods, etc. Having an established population would reduce both the expense of product as well as the task of regular dosing. This is why so many aquarists are now experimenting with techniques aimed at accomplishing that very objective–-creating an ideal niche for PNSB. Kind of like when we worked so hard collectively to master the culture of nitrifying bacteria back in the 70s and 80s…
Let’s not yet get disheartened by the apparent paucity of PNSB in our systems. There remains a lot to learn here. First, how many of the tanks cited in those Aquabiomics reports had ever dosed PNSB? Any? Was there any attempt to provide an appropriate biomedium for them? And how were these samples taken? We know that PNSB live in two distinct microhabitats within an aquarium that are unlikely to be sampled: Anaerobic zones and mucus/tissues of the living corals themselves. Thus, prior tests may easily have underrepresented PNSB as they typically occur in captive systems. I don’t know of many hobbyists who dose PNSB and have independently sent samples to Aquabiomics for analysis. However, to my knowledge, there are individuals working on that as I write this. As many aquarists try different biomedia, cultivation methods etc. and share Aquabiomics reports, we’ll get a better idea of what we may best do to promote bigass, persistent populations of PNSB. And of other probiotics such as Bacillus, and so on. And if more investigation reveals that the typical reef aquarium simply cannot support permanent establishment of these very natural and very beneficial bacteria? Then the argument will be whether or not there is an explicit advantage to adding them via a regular dosing regimen. Considering their demonstrated nutritional/probiotic benefits as stony coral symbionts alone (which I observe and hear about from others daily), I think I already know where I’ll stand on that one.
