A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It a
dheres to the intestinal lining using a feature that also protects it from bacteriophages and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. This bacterium derives nutrition by digesting human intestinal contents (in other words, food). Humans lacking this bacterium have no measurable reproductive advantage or disadvantage relative to humans who harbor this bacterium. Consequently, the bacterium can be properly described as which of the following? (1). symbiont
(2). endotoxin
(3). mutualist
(4). commensal
The bacterium inside the human intestine is a symbiont and the bacterium-human interaction is a symbiosis of the commensalistic type.
Commensalism is a biological interaction (symbiosis) in which members of one species -in this case the bacterium- gain benefits while those of the other species -in this case the human- neither benefit nor are harmed.
