Post originally by JRM at 2004-07-28 09:51:50
Converted from Phorums BB System

Just to be pedantic, chemosynthesizers don't make sugar from Hydrogen Sulfide. You need Carbon to make a Carbohydrate, and there ain't any in H2S. The micro-organisms use Hydrogen Sulfide as a fuel, by oxidizing it, and may use this energy to make a sugar using Carbon from another source, such as Methane or Carbon Dioxide.

Incidentally, the micro-organisms that digest Sulphates use it as an oxidizer. They reduce the Sulphate to get the oxygen out, then use the oxygen to "burn" a fuel. I think most of them use Methane, but haven't bothered to look it up. It costs the microbe less energy to break the oxygen out of the Sulphate than they gain from burning the fuel, so they end up in the black.

Unless you're roleplaying a bunch of biochemists, this probably won't matter. However, as Conall said, these microorganisms could be the basis for a food chain in underground environments, some of which could be very hostile to adventurers.

To start with, Hydrogen Sulfide itself is a poisonous gas (as I learned in O-level chemistry) with symptoms resembling cyanide / carbon monoxide poisoning - i.e. headaches, chocking, turning blue and sudden death. According to the Emergency Medicine website (see http://www.emedicine.com/EMERG/topic258.htm) "Exposures of 700-800 ppm or greater usually result in death".

Furthermore, H2S it forms Sulfuric Acid when mixed with water. There are caves in the Yucatan that have so much H2S and H2SO4 in the air that scientists have to wear gas-masks to study its chemosynthesis-based ecology (it still has atmospheric oxygen, but they need to filter out the acid). The caves sustain a lot of invertebrates and even fish who are adapted to breathe the acidic air/water. Apparently, at least one of these sulphur-based ecologies is able to support bats! (see http://www.norwebster.com/speleoscope/speleo01.html)