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#           Stimulation of aquatic bacteria from Mammoth Cave, Kentucky, by sublethal concentrations of antibiotics      

      May 1, 2023    

Many microorganisms secrete secondary metabolites with antibiotic properties; however, there is debate whether the secretions evolved as a means to gain a competitive edge or as a chemical signal to coordinate community growth. The objective of this research was to investigate if select antibiotics acted as a weapon or as a chemical signal by exposing communities of aquatic cave bacteria to increasing concentrations of antibiotics. Water samples were collected from six cave locations where actinobacterial mats appeared to be plentiful. Bacterial growth was measured using colony counts on 10 % tryptic soy agar augmented with increasing concentrations of erythromycin, tetracycline, kanamycin, gentamicin, or quaternary ammonia compounds (QAC). Colony counts generally decreased as the gentamicin, kanamycin and QAC dose increased. In contrast, the colony numbers increased on agar plates supplemented with 0.01 mg L−1, 0.10 mg L−1 and 1.00 mg L−1 erythromycin or tetracycline. A 10.00 mg L−1 dose of each antibiotic treatment reduced bacteria colonies by 98 % or more. Community-level physiological capabilities were evaluated using Ecolog plates inoculated with cave water dosed with either 0.00 mg L−1 or 0.10 mg L−1 of erythromycin. Incubation with the antibiotic almost doubled the number of food substrates used in the first 24 hours. There was a significant increase in the use of acetyl glucosamine, arginine, and putrescine when bacteria were exposed to 0.10 mg L−1 erythromycin triggered by the antibiotic acting as a chemical messenger. Principal component analysis confirmed a shift in substrate preferences when erythromycin was added. A conceptual ecological model is proposed based on the response of aquatic cave bacteria to sublethal antibiotics. 

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January 11, 2021

####                 Average well color development data for water samples from six locations within the historic section of Mammoth Cave National Park, Kentucky              

Cooperative Research Units, Lower Mississippi-Gulf Water Science Center

#### Thomas D Byl, Ph.D.

##### Research Biologist

Lower Mississippi-Gulf Water Science Center

tdbyl@usgs.gov

615-837-4750

## Related Content

January 11, 2021

####                 Average well color development data for water samples from six locations within the historic section of Mammoth Cave National Park, Kentucky              

Cooperative Research Units, Lower Mississippi-Gulf Water Science Center

#### Thomas D Byl, Ph.D.

##### Research Biologist

Lower Mississippi-Gulf Water Science Center

tdbyl@usgs.gov

615-837-4750

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#### Lower Mississippi-Gulf Water Science Center - Nashville, TN Office

640 Grassmere Park DriveNashville, TN37211United States

GS-W-TNnsh Webmaster@usgs.gov

(615) 837-4700

(615) 837-4799 

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