You are Indestructible

Whenever a player taps a land for mana, this enchantment deals 1 damage to that player.

You can't get poison counters. Creatures you control can't have -1/-1 counters put on them. Creatures your opponents control lose infect.

You don't lose the game for having 0 or less life. As long as you have 0 or less life, all damage is dealt to you as though its source had infect. (Damage is dealt to you in the form of poison counters.)