How many bugs?
How many different kinds of bacteria are there on earth, and how does that compare to the few we know of so far? The true answer to those questions is that we don’t yet know, but we may be coming closer to an answer. Microbiologists have formally described 5,000 microbial ‘species’, but this barely scratches the surface. Some estimates suggest that there are probably more than 500,000 kinds of bacteria on Earth.
My own work a couple of years ago show that it’s not too difficult (armed with the right molecular tools) to find novel microorganisms (in my case, viruses). All you need a horse and a PCR machine. Armed with those two common household objects, we were able to find a couple of hundred new viruses without too much difficulty.
Similarly, it’s easy to find a few thousand distinct kinds of microbes in a litre of seawater, but the question then becomes, is that all there is? How do we know when to stop counting? A PNAS paper looking at the “rare biosphere”, that’s to say the ocean depths (which are less well studied than other planets in our solar system) shows that microbial diversity in the oceans (and elsewhere) is much greater than previous estimates based on conventional molecular techniques. Rather than the 1,000 to 3,000 expected, this study found more than 20,000 distinct bacteria in a single litre (about a quart) of seawater.
So how many bugs are there out there? We still don’t know. Keep counting.
hey ya’ll,
Here are a two other numbers and a question:
Brazilian researcher Marcio Lambais and his team from the University of Sao Paulo counted bacteria in the phyllosphere of 9 different tree spezies in the Atlantic forest of Brazil. Their calculations indicate that each tree of the forest could harbor anywhere between 95 and 671 different bacterial species. That could amount to 2 million to 13 million different bacterial species for the whole forest.
Science 30 June 2006: Vol. 312. no. 5782, p. 1917.
Found over at the biosingularity weblog:
Steven Gill and his colleages from the TIGR institute found that in the human colon 10 to 100 trillion bacteria of over 1000 different species thrive.
Science 2 June 2006: Vol. 312. no. 5778, pp. 1355 – 1359
And the question:
How many bacteria of how many species could there be in the whole human body? Is the colon community by far the biggest community?
Greetings,
Andreas Bäumer
The number from Steven Gill is fairly typical of those found by other researchers, although there are some slightly higher estimates. Because it’s nutrient rich, most people believe the colon probably has the richest bacterial flora in the body (that’s why we did our virus study on horse faeces – it’s easier waiting for the bugs to come out of the colon than going inside!). In fact, the whole of the digestive tract is rich in species, e.g. there are a lot of species between your teeth, although perhaps rather less in the extreme environment of the stomach.
The lower number of species from Marcio Lambais is typical of natural environments. The interesting thing is that most researchers have used similar, PCR-based methods, and come up with similar numbers. That’s why the Sogin PNAS paper is significant in this now rather crowded field. Because they found 10 times more species in seawater than such studies typically do, it suggests that the total number of species on the planet may be much higher than previously thought.
BTW Andreas, nice blog!
Alan: great idea!! Of course, our bandwidth at the University of Cape Town is too low for us to actually LISTEN to a podcast in anything approaching real time , but I will go home and do it from there (DSL line).
A great project; I look forward to seeing how it develops.
Ed Rybicki
I realize that bandwidth is still a problem for many people, but the situation is improving all the time. The mp3 file are as small as I can make them with reasonable sound quality (although the enhanced version files sound better and have lots of groovy extras included), but if anyone else is having problems, please let me know.
[...] A while back, I wrote about how many different kinds of bacteria are there on Earth. This proved to be a very popular topic, so in this week’s podcast, I describe recent work which explores a more direct but still not a simple question: How many different bacteria are there in a gram of soil? As the podcast describes, it’s not as easy to find out as you may think, but in summary, results suggest that in Alaskan soil there are 4,000 bacterial species per gram, and in soil from Minnesota, 10,000 per gram. Interestingly, only approximately 20% of the bacteria appear to be present in both soils, a perhaps unexpected degree of geographical variation. There’s a lot of bugs out there! [...]
[...] How many bugs? [...]
so how many BUGS are there this only talks about bacteria