July 17 (UPI) -- New research shows bacteria passed directly across generations, from mom to offspring, are more essential than bacteria acquired from the environment.
The study, published this week in the journal Nature Communications, offers scientists a better understanding of bacterial symbiosis.
Only a small percentage of bacteria is harmful. Most strains and species are harmless. Some bacteria are not just beneficial to their hosts, but essential.
Zoologists at the University of Oxford, in England, analyzed the evolutionary history of 106 bacterial symbioses among animal, plant and fungi species. They found bacteria passed vertically -- from mother to offspring -- are more beneficial to the organism's health than bacteria acquired from the environment.
Species evolve to depend on many of the vertically acquired bacteria strains. Aphids, small sap-sucking insects, die when robbed of their vertically acquired bacteria.
Bacteria acquired from the environment can still prove beneficial. Rhizobia bacteria, for example, is acquired by pea and bean plants from the soil and helps the plants absorb nitrogen gas from the atmosphere and use it as fuel. Take the bacteria away, however, and the plants won't die.
"If a bacteria is passed on vertically, it has a vested interest in its host's wellbeing," Stuart West, a professor of zoology at Oxford, said in a news release. "A healthy host, who is doing well, will produce more offspring, and in doing so, it will also pass on its bacteria as well."
"These offspring will then follow the same cycle with the next generation, and so on. The vertically transmitted symbionts have a lot to gain from a healthy, happy host," West said. "Whereas those passed on horizontally, via the environment, are less invested in their host's fitness and wellbeing, since it has no bearing on their own success."