Abstract
Marine natural products isolated from the sponge Fascaplysinopsis cf reticulata, in French Polynesia, were investigated as an alternative to antibiotics to control pathogens in aquaculture. The overuse of antibiotics in aquaculture is largely considered to be an environmental pollution, because it supports the transfer of antibiotic resistance genes within the aquatic environment. One environmentally friendly alternative to antibiotics is the use of quorum sensing inhibitors (QSIs). Quorum sensing (QS) is a regulatory mechanism in bacteria which control virulence factors through the secretion of autoinducers (AIs), such as acyl-homoserine lactone (AHL) in gram-negative bacteria. Vibrio harveyi QS is controlled through three parallel pathways: HAI-1, AI-2, and CAI-1. Bioassay-guided purification of F. cf reticulata extract was conducted on two bacterial species, i.e., Tenacibaculum maritimum and V. harveyi for antibiotic and QS inhibition bioactivities. Toxicity bioassay of fractions was also evaluated on the freshwater fish Poecilia reticulata and the marine fish Acanthurus triostegus. Cyclohexanic and dichloromethane fractions of F. cf reticulata exhibited QS inhibition on V. harveyi and antibiotic bioactivities on V. harveyi and T. maritimum, respectively. Palauolide (1) and fascaplysin (2) were purified as major molecules from the cyclohexanic and dichloromethane fractions, respectively. Palauolide inhibited QS of V. harveyi through HAI-1 QS pathway at 50 μg ml–1 (26 μM), while fascaplysin affected the bacterial growth of V. harveyi (50 μg ml–1) and T. maritimum (0.25 μg). The toxicity of fascaplysin-enriched fraction (FEF) was evaluated and exhibited a toxic effect against fish at 50 μg ml–1. This study demonstrated for the first time the QSI potential of palauolide (1). Future research may assess the toxicity of both the cyclohexanic fraction of the sponge and palauolide (1) on fish, to confirm their potential as alternative to antibiotics in fish farming.
Highlights
The overuse of antibiotics in the environment may have important economic and sanitary outcomes (Martinez 2009; Hatosy and Martiny 2015)
The purification of the cyclohexanic fraction conducted to the known palauolide (1) (0.005 g, yield 0.005% w/w) and the dichloromethylenic fraction to the alkaloid fascaplysin (2) (0.019 g, yield 0.02% w/w) (Fig. 1)
During the growth of V. harveyi bacterial strains, the growth rate (k parameter) of absorbance increased as the concentration of palauolide (1) increased (Table 1, Fig. 2c)
Summary
The overuse of antibiotics in the environment may have important economic and sanitary outcomes (Martinez 2009; Hatosy and Martiny 2015). The release of antibiotics in natural environments exerts a strong pressure on bacteria strains and supports the selection of resistant bacteria. The recurrent use of antibiotics decreases their effectiveness over time (Blair et al 2015). To reduce the overuse of antibiotics and minimize the impacts to the environment and human society, there is. In aquaculture antibiotic resistance causes mass mortality of cultured species (Karunasagar et al 1994) which result in economic loss for farmers (Shrestha et al 2018). Aquaculture itself largely contributes to the dissemination of antibiotics resistance genes in the aquatic environment (WHO, 2006; Shah et al 2014), which increases the risks on human health (Aly and Albutti 2014). Finding antibiotic alternatives in this field is the focus of the current research (Pérez-Sánchez et al 2018) due to
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