Bacteria are classified into four groups according to their means of obtaining nutrients:
The photoautotrophs make food via the process of photosynthesis, using sunlight and carbon dioxide. These include cyanobacteria.
The photoheterotrophs use photosynthesis but cannot use carbon dioxide. These bacteria need to obtain carbon from another source.
The chemoautotrophs gain energy from inorganic substances and get their carbon from carbon dioxide.
The chemoheterotrophs obtain energy from inorganic substances but cannot use carbon dioxide as their carbon source. Most pathogens are chemoheterotrophs. This group is further broken down based on how carbon is obtained:
parasites obtain nutrients from a host.
saprobes obtain nutrients from wastes or the remains of other organisms.
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