Oxytetracycline and Ciprofloxacin Exposure Altered the Composition of Protistan Consumers in an Agricultural Soil

Protists,
an integral component of soil microbiome, are one of
the main predators of bacteria. Bacteria can produce toxic secondary
metabolites, e.g., antibiotics to fight stress under the predation
pressure of protists; however, impacts of antibiotics on the profile
of protists in soils remain unclear. Here, we constructed a microcosm
incubation to investigate the effects of two common antibiotics, oxytetracycline
and ciprofloxacin, on the protistan and bacterial communities in an
arable soil. Rhizaria were the most abundant protist supergroup, followed
by Amoebozoa, Stramenopiles, and Aveolata. Among trophic functional
groups, consumers were predominant within the protistan community.
The protistan alpha-diversity was not significantly changed, while
the bacterial alpha-diversity was decreased under the pressure of
antibiotics. Nevertheless, the antibiotic exposure considerably reduced
the relative abundance of protistan lineages in Rhizaria and Amoebozoa,
which were the dominant supergroups of protistan consumers, while
increased the relative abundance of other consumer and phototrophic
protists. Altogether, we provide novel experimental evidence that
the bacterivorous consumers, an important functional group of protists,
were more sensitive to antibiotics than other functional groups. Our
findings have potential implications for the induced alterations of
protistan community and their ecological functions under the scenarios
of projected increasing global antibiotic usage.