(Not) Spontaneous Generation

Spontaneous generation is a (once widely held) belief that organic matter contains a vital force that can spawn life from inanimate objects.

Spontaneous generation was first disproved in the case of macro (large) organisms when, in 1668, Francesco Redi debunked the idea that meat exposed to the environment could spontaneously generate maggots. He thought maggots arose from eggs laid on the meat by flies.

The following is a figure illustrating his experimental design (taken from here).

In the middle treatment, a piece of meat was overlaid with cheesecloth. The flies were able to lay the eggs into the cheesecloth and when this was removed no maggots developed. However, if the cheesecloth containing the eggs was placed on a fresh piece of meat, maggots developed, showing it was the eggs that "caused" maggots and not spontaneous generation.

In 1794 John Needham provided what he considered to be proof of the spontaneous generation (SG) of microorganisms, when he heat-treated chicken broth which later developed a thriving microbial community after being cooled, and left at a constant temperature.

Of course, the flask was exposed to air. When Lazzaro Spallanzani conducted the experiment again, this time modifying the design so that air was excluded from the heated broth, no microorganisms manifested. This is was not the end of the affair though, as proponents of SG countered that air was necessary to somehow activate the vital force. 

Pasteur put paid to SG about 100 years later (remember, this was in the late 1800's, not that long ago). First he demonstrated that air contained particulate matter bearing what looked suspiciously like microorganisms. Secondly, he demonstrated (creating the swan-necked flask in the process) that heated organic matter exposed to air only spawned microbial colonies if the particulate matter carried in the air was allowed to reach the organic matter. See figure below (also from here).

Both flasks are open to the air, but if the air is heated at the u-bend to kill microbes piggy-backing on dust particles no microbial colonies manifest. Air doesn't activate a vital force because, well, there ain't one....

Below is a photo of a 60L plastic tub in my backyard that contains a small population of Utricularia australis - an aquatic, carnivorous plant. Members of the genus are called commonly called bladderworts after their tiny suction traps. The bladderworts are, however, not the stars of this post. 

An outdoor aquarium for bladderworts. The small bottle with the green cap at the left is a DIY CO₂ generator - increased dissolved CO₂ gives submerged aquatic plants a boost for photosynthesis.

I made up the tank from scratch using peat, sand, some leaf matter and rainwater. I transplanted a few companion plants, the bladderworts themselves, and inoculated the tub with a jar of water from the lake of origin to provide a source of prey.

What I most certainly didn't put in the tank was this:

The wily "Corinichthyes"

... At least not knowingly, and not in their current form. My partner was the first person to spot them, about two days before this picture was taken. When told I was incredulous, something not helped by their habit of hiding at the bottom of the tub when approached. Eventually I spotted them, and it did indeed seem truly miraculous. 

They have been dubbed "Corinichthyes" pending further identification. Given the history of the lake where the bladderworts and water came from, I suspect they are a trout fry.