POTENTIAL
USE
OF
METHYLTESTOSTERONE
SYSTEMS
BACTERIAL
DEGRADATION
TO
ELIMINATE
FROM INTESIVE TILAPIA MASCULINIZATION
Rosa M. Padrón-López1, Lucero Vázquez-Cruz1, Ulises Hernández-Vidal2, Wilfrido M.
Contreras-Sánchez*2 and Kevin Fitzsimmons.
1
Laboratorio de Microbiología. e-mail: lucerovc@gmail.com; 2Laboratorio de Acuicultura
Tropical. División Académica de Ciencias Biológicas, Universidad Juárez Autónoma de Tabasco,
km 0.5 carret. Villahermosa–Cárdenas, Col. Bosques de Saloya, 86039, Villahermosa, Tabasco,
México
To reduce the potential contamination of effluents with Methyltestosterone (MT) used in Tilapia
hatcheries, we have proposed the use of bacteria isolated from filters that trap MT in activated
charcoal. MT is commonly used in tilapia aquaculture to produce all-male populations and
certain concerns have been raised regarding the potential risks to the environment and farmers.
The filters we use to retain MT have a biofiltration component where microbial populations are
easily formed. We hypothesized that some of the MT degradation occurs in the biofilter due to
the active use of MT as carbon source. Based on this we isolated and characterized heterotrophic
bacteria obtained from biofilms formed in a filtration system used for tilapia (Oreochromis
niloticus) masculinization. We also determined the capacity of adaptation of isolated bacteria in a
culture media enriched with MT as the only source of carbon. Primary isolates were obtained
from biofilms collected at 7, 11, 20 and 28 days of the masculinization trial. Isolates were
inoculated in nutritious agar and eosin-methylene blue agar. Identification was conducted using
API WEB and dichotomic keys (Koneman et al.,1999). Adaptation trials were conducted in
flasks containing mineral medium enriched with MT (45 mg/100 ml) as the only carbon source.
Each flask was inoculated with 2ml of a bacterial suspension (0.5 in the McFarland scale) and
incubated at 30 ºC with agitation at 175 rpm for 26 days. Adaptation was measured by counting
bacteria daily using the plate counting method.
We isolated and characterized Bacillus ceresus, Bacillus subtilis, Pseudomonas aeruginosa,
Pseudomonas fluorescens and Serratia marcescens. All of them were able of using MT as source
of carbon and energy. P. aeruginosa was the species with the fastest adaptation; initial growth
was perceived at 48 hours and reached the highest number of microorganisms. B. subtilis y P.
fluorescens showed initial growth at 72 hours while B. ceresus y S. marcescens initiated growth
later (96 and 198 hours, respectively (Fig. 1). P. aeruginosa seems to be a species capable of
utilizing a large amount of organic compounds as substrate to grow. This capability allows it to
colonize niches and inhospitable environments where nutrients are scarce. Our results indicate
that the bacteria we isolated are potential MT biodegraders.
Figure 1. Growth kinetics of bacteria in mineral medium
enriched with MT.
P. aeruginosa;
B. ceresus;
B. subtilis,
P. fluorescens;
S.
marcescens.
10000000
1000000
UFC/ml
100000
10000
1000
Funding for this research was provided by F&A CRSP. Project
07MNE06UA under Grant No. EPP-A-00-06-00012-00 from the
United States Agency for International Development (USAID)
100
10
1
24 48 72 96 120 144 168 192 216 150 174 198 222 246 270 294 318 342 366 390 414 438 462 486 510
Horas
P.a
B.c
B.s
P.f
S.m