How can we make bacteria that metabolize waste plastic?

Answered Jul 31, 2019

You wouldn’t necessarily “make” microbes that can do this.

There is at least one species of fungus that can break down certain types of plastic to use for food.

However, there are various problems. Some of which are biological, and some are physical.

The “plastic-eating fungus” uses enzymes called esterases, which will only work on certain classes of polymers that are structured a certain way.

Also, a chunk of plastic will only be vulnerable to reactions on its surface, which might take a long time to eat all the way through. Plus, if I recall correctly, there is a physics thing called “water activity”, which is necessary for the enzymes to work, but is going on at very low levels on the surface of the plastic (even with the fungus and/or enzymes present).

Attempting to insert the enzyme gene into bacteria for mass production has various biological problems, including protein folding, toxicity to the bacteria, etc.

If mankind hit a maximum population limit, will we resort to “population control”? Or will we have enough time to expand to other worlds before it gets to that point?

Answered Jul 5, 2019

First, you can forget about the “expand to other worlds” idea.

Space travel is hugely expensive, in money, technology, and time. It is a major set of problems just to get a car-sized machine to the Moon or to Mars.

For humans, space travel is also dangerous, from launching a rocket, to landing, to the reliance on life-support systems, to the long-term effects of low-gravity, radiation, and living inside vehicles, stations, etc.

If you go to the Moon or Mars, you need to bring all of your resources with you, to last your entire stay. Hugely expensive to get it all there, even for just a few days visit. Uncrewed resupply craft are expensive, take a long time to reach Mars, and might crash or otherwise be lost.

Changing the atmosphere on the Moon or Mars (so you could go outdoors without a spacesuit) would take enormous physical resources, and centuries of time, and may be physically impossible. Temperatures and radiation may also be insurmountable issues. Living permanently inside protective structures would be extremely expensive.

As I understand it, chemical analysis of Martian soil suggests that it might be impossible to ever grow plants or fungi in it.

There are fantasies of geological mining of the Moon and Mars. Which would require hugely expensive machinery and other resources, which make Earthly colonisation and resource-extraction (e.g. centuries-past North America and Africa) look cheap and easy by comparison.

Forget about the other planets and their moons. Heat, radiation, pressures, toxic gasses, planets made entirely of gasses, or solid but really cold planets and moons.

Forget about ever visiting any planet outside our solar system. The distances are too great, the expenses too high, and the timeframe too long.

So, back to the real world…

Maximum population is contextual, in place, time, and technology.

This was described back in 1798, by Thomas Malthus. The idea is that, population control is a natural, universal mechanism, affecting all life-forms.

Malthus observed that, population numbers increase based on food supply. This can be plants with plentiful space/water/nutrients, herbivores with plentiful plants available, or carnivores with plentiful prey available. It can also be humans with increasing agricultural efficiency and technology.

While microbiology wasn’t understood in Malthus’s time, the principle includes single-celled organisms, which have a common growth curve of increasing exponentially, and then leveling off.

The population will increase to the contextual maximum, where everyone is just barely obtaining/producing enough to survive.

Then, there are two suppressing scenarios:

  1. Something reduces the food supply at some level of the food chain or food web. It could be an especially harsh winter, or an extended drought, or a disease of plants or animals. Starvation ensues.
  2. The food supply remains stable, but the population compulsively keeps reproducing/expanding, and overshoots the supply. Starvation ensues.

This may be cyclic. Food-suppressing events like weather and diseases will occur either yearly, or repeatedly over a longer timeframe. Humans improve technologically, overshoot the population, and suffer until the next big improvement.

There may be hard, regional or global upper limits on food production, fresh waters, etc. Where humans will never be able to improve efficiency past the Earth’s “carrying capacity”.

Another suppressor is communicable diseases.

Increased population leads to increased crowding, leads to increased disease transmission. Anything from the medieval plagues to the 1918 influenza could replay. Global warming may increase the geographic range of malaria-carrying mosquitoes.

High-intensity farming (to feed the current overpopulation) may increase the risk of microbial diseases of plant crops and animal livestock, leading to famine, and starvation of humans.

Another pressure is interspecies and intraspecies competition. A slightly more efficient (for the particular environment) species may out-compete other species, who may then starve. Animals – either individuals or groups – may compete with others of their same species.

The highest level of this is human warfare, which is always (either overtly or thinly disguised) economically motivated. Humans fight over farmland, water, or natural resources (oil, mining, forestry, fishing) which can be used or sold. Which ultimately leads to food and other means to support the population numbers of a particular country or tribe.

Even losing sides can do great damage. This includes ancient retreating armies pouring NaCl salt onto the ground, to impair future farming use, up to modern retreating armies setting oil wells on fire.

Conflicts which are ostensibly about religion or ethnicity are really just using those characteristics to organise and motivate groups for economic competition over natural resources.

In warfare, both sides will have many people killed, or die from degraded conditions, including starvation, diseases, etc. The losers may be completely genocided.

Warfare can be a means of increasing one’s own tribal population. However, it can also result in mass burning-off of surplus impoverished young males (i.e. “cannon fodder”).

Another aggressive angle is China’s “one-child policy”. It seems abusive and micromanaging, but the alternative is, ultimately, mass starvation. China has a mismatch of a high percentage of the world’s people, and relatively low percentage of the world’s farmland.

A gentler angle is advancements in contraception technology and distribution of it. Personally, I strongly support government efforts for free, easy contraception to anyone and everyone who will accept it. Anything from handing out condoms to offering cash payments for welfare recipients to get long-term implants or permanent sterilisation.

All of this sounds somewhat unpleasant to some people. But those people cannot imagine how unpleasant things would be with 20 billion humans on the only planet we will ever have.

And, lest anyone think to accuse me of any kind of hypocrisy or snobbery… I am childfree, never wanted any sprogs, and going to stay that way. At an age and condition where I actually do know what I am talking about on that.

Why is New Zealand not recycling? Is New Zealand not recyling?

Answered Dec 21

Other commentators have focused on the actions of households. The problem is the ultimate destination of the material.

On the surface, there appears to be plenty of recycling occurring. Cities have recycling bins available, and pick up the contents weekly.

But where does it go?

Into a big pile.

The reasons are economic.

The material must be transported to a recycling facility. Which may be hundreds of kilometres away. Or may be overseas, such as in China. The cost of transport may be higher than the market value of the material.

What do you do when the Chinese government restricts importation of the material?

Put it in a big pile, right here in New Zealand.

An alternative is sending it to Malaysia. Where they put it in a big pile, and openly burn it.

NZ’s recycling crisis after China ban: ‘This situation is not sustainable’

New Zealand’s plastic stockpile is at 400 tonnes and could be going mouldy

Kiwis’ recycling is piling up in Malaysia and being burnt in secret, environmentalists say

What would happen if there were no plants on earth?

Answered Dec 18, 2017

I am guessing that you mean, “If all the plants disappeared right now”(?)

All humans and other terrestrial animals (e.g. livestock like cattle and chickens) would starve to death. Most people would be dead within a year, from immediate shortages, and competition/conflict over dwindling resources.

Anyone living longer would need to have stockpiles of grains, rice, canned goods, or other long-shelf-life food. They would still die when that ran out.

On a very long-term scale, the atmosphere would change, due to the lack of CO2 uptake, and the lack of O2 being pumped out.

All animals (including carnivores) are directly or indirectly dependent on plants.

On a more positive note, many of the bacteria, archaea, and fungi would still survive, although the balance of particular species would gradually change with the new environmental conditions.

Are there any study to design bacteria so they can produce all essential nutrients by photosynthesis?

Answered Dec 15, 2017

Thanks for the A2A.

The answer is “no”, because photosynthesis is about using the energy from sunlight, to help use carbon dioxide as a building-block to put together sugar molecules, which are made of carbon, hydrogen, and oxygen. Those sugars function as energy storage (which is how plants survive every night), and also as building material, which is how plants grow new stems, leaves, etc.

Some bacteria can do photosynthesis for sugar-assembly, but there are many other essential nutrients.

If the organism has the necessary enzymes, they can use certain “carbon skeletons” (including acetyl-CoA and Krebs cycle intermediates) as building blocks for lipids and part of amino acids.

However, it still needs to get certain other, vital things from the environment (which cannot be generated by photosynthesis, either by bacteria or by plants).

It needs things like:






Those need to be obtained from the environment, which can be anything from the jelly-like medium in a petri dish, based on various recipes, by microbiologists (ahem), to just the regular, random soil in your backyard (different places support different microbes).

Another commentator seemed to interpret your question as being about food for humans. And the answer on that is “no”, because your food needs to get the above-listed nutrients from someplace that isn’t just photosynthesis.

What would the earth be like if there are no bacteria to decompose animal and plant remains?

Updated Feb 6, 2018

Those are called saprophytes, although there is a wide range, and some fungi also perform this function.

If no decomposition was happening at all, then the nutrients wouldn’t be available for recycling into plants, so my guess is that all other life on earth would eventually starve. It might take awhile.

Also, partly decayed plant and animal matter is among the things consumed by worms, insects, etc, so it would disrupt the food-chain / food-web from that angle, as well.

Edited To Add: Another group of bacteria whose absence would be disastrous are the participants in the nitrogen cycle, because all plants need nitrogen in a form that is generated by those bacteria.

Edited To Add Again: I recall reading an article stating that, plant matter (fallen leaves, etc) near the Chernobyl nuclear disaster site wasn’t breaking down as normal. If true, that suggests that, the radiation has harmed a range of saprophyte bacteria and fungi. This could have a sort of secondary impact on the ecosystems there, for future plants and animals.