Abstract
Diatoms, such as Chaetoceros, grow in a mutualistic relationship with bacteria. However, in some cases, it is necessary to grow them in bacteria-free cultures. To reduce bacterial load, antibiotics are used, and on certain occasions it is necessary to use a mixture with more than one antibiotic. This work aimed to obtain a quick and effective protocol to reduce the bacterial load and evaluate the response of three Chaetoceros species with aquacultural importance. Single and mix antibiotics were used. Microalgal and bacterial growth was measured. The growth parameters for diatoms showed that the significantly highest cell concentration was for C. muelleri (3.15 x106 cells mL-1) and the lowest values to C. calcitrans (2.98 x106 cells mL-1). The significantly highest growth rate was for C. calcitrans (0.77 divisions per day), and the lowest values for Chaetoceros sp. (0.60 divisions per day). The growth parameters for heterotrophic bacteria showed that the significantly highest bacterial load was for Chaetoceros sp. (19.16 x106 CFU (Colony-Forming Units) mL-1) and the lowest values were for C. calcitrans (12.23 x106 CFU mL-1). The growth rate of the heterotrophic bacteria present in Chaetoceros cultures was similar among the three studied species. Streptomycin® and sulfate G41® produced a partial reduction of bacterial load. The most effective treatment for all three species was the use of an antibiotic mix composed of ampicillin® (250 μg mL-1), kanamycin® (200 μg mL-1), neomycin® (50 μg mL-1), and streptomycin® (100 μg mL-1) for three days. The mix prepared with the highest antibiotic concentration produced a reduction of bacteria (100%) for three days; however, it also induced a significant reduction of the growth of the three Chaetoceros species.
Highlights
Diatoms are highly diverse photosynthetic organisms characterized by its silica frustules (Leynaert et al 2018)
Microalgae and bacterial growth The growth curve shows that C. muelleri and C. calcitrans had an exponential growth phase until day 4, after which the stationary-growth phase began, and during day 7, a decrease in cell concentration was evaluated
The growth parameters for heterotrophic bacteria show that the significantly highest bacterial load was for Chaetoceros sp. (19.16 x106 CFU mL-1) and the lowest values for C. calcitrans (12.23 x106 CFU mL-1; P < 0.05)
Summary
Diatoms are highly diverse photosynthetic organisms characterized by its silica frustules (Leynaert et al 2018) They are cosmopolite organisms that can be found in marine and seawater environments and are responsible for 20-25% of global primary production (Bozarth et al 2009). Chaetoceros is a primarily marine genus and one of the most abundant, reaching almost 228 described species (Guiry & Guiry 2021). (CHX1) was isolated in 1988 from Todos Santos Bay at Baja California, Mexico (Trujillo-Valle 1993). This strain has a high potential to be used on aquaculture due its high population growth rates and biochemical composition (Sánchez-Saavedra & Voltolina 1995, 2001, 2006). The species identification has remained uncertain, but it seems to be a strain of Chaetoceros gracilis (Tapia-Gallardo 2019)
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