CHARACTERIZATION OF SUPERNATANT EXTRACT AND VIABILITY OF BACILLUS SUBTILIS KM16 AND PSEUDOMONAS SPP. IN FISH FEED AS BIOCONTROL AGENTS AGAINST AQUACULTURE PATHOGENS

The use of biocontrol agent in aquaculture is being adapted as an effective alternative to antibiotics which can lead to the elaboration of antibiotic-resistant bacteria and confer unpleasant impacts to aquatic organisms. Aquatic bacteria have been discovered as biocontrol agents and potential probiotic candidates to improve the health of aquatic organisms, feed efficiency, and disease resistance to aquaculture pathogens. However, local isolate has not intensively been explored and used to increase aquaculture sector productivity. Therefore, this research aimed to determine minimum inhibitory concentrations of their antibacterial compounds against aquaculture pathogens and to characterize aquatic bacteria by their viability in the feed. Four isolates from several aquatic environments in Indonesia (Pseudomonas sp. S1.1, Pseudomonas sp. S1.2, Pseudomonas sp. SL1.1, and Bacillus subtilis KM16) were used to characterize of antibacterial compound and to determine the viability in feed. Ethyl acetate extracts from all isolates showed better antibacaterial activity against Aeromonas hydrophila and Vibrio vulnificus than chloroform and dichloromethane extracts, in which ethyl acetate extract from Bacillus subtilis KM16 showed the strongest antibacterial activity. Pseudomonas spp. were more effective against V. vulnificus (40 mg/mL) and Bacillus subtilis KM16 was more effective against A. hydrophila (20 mg/mL), as proved by the minimum inhibitory concentrations of their ethyl acetate extracts. In this research, Bacillus subtilis KM16 had stable viability in feed than Pseudomonas sp. isolates.

The Hydric Environment: A Hub for Clinically Relevant Carbapenemase Encoding Genes

Carbapenems are β-lactams antimicrobials presenting a broad activity spectrum and are considered as last-resort antibiotic. Since the 2000s, carbapenemase producing Enterobacterales (CPE) have emerged and are been quickly globally spreading. The global dissemination of carbapenemase encoding genes (CEG) within clinical relevant bacteria is attributed in part to its location onto mobile genetic elements. During the last decade, carbapenemase producing bacteria have been isolated from non-human sources including the aquatic environment. Aquatic ecosystems are particularly impacted by anthropic activities, which conduce to a bidirectional exchange between aquatic environments and human beings and therefore the aquatic environment may constitute a hub for CPE and CEG. More recently, the isolation of autochtonous aquatic bacteria carrying acquired CEG have been reported and suggest that CEG exchange by horizontal gene transfer occurred between allochtonous and autochtonous bacteria. Hence, aquatic environment plays a central role in persistence, dissemination and emergence of CEG both within environmental ecosystem and human beings, and deserves to be studied with particular attention.

Warming-enhanced priority effects at population and community levels in aquatic bacteria

The immigration history of communities can profoundly affect community composition. For instance, early-arriving species can have a lasting effect on community structure by reducing the immigration success of late-arriving ones through priority effects. Warming could possibly enhance priority effects by increasing growth rates of early-arriving bacteria. Here we implemented a full-factorial experiment with aquatic bacteria where both temperature and dispersal rate of a better-adapted community were manipulated to test their effects on the importance of priority effects, both on a community and a population level. Our results suggest that priority effects in aquatic bacteria might be primarily driven by niche preemption and strengthened by increasing temperature as warming increased the resistance of recipient communities against dispersal, and decreased the relative abundance of successfully established late-arriving bacteria. However, warming-enhanced priority effects were not always found and their strengths differed between recipient communities and dispersal rates. Nevertheless, our findings highlight the importance of context dependence of priority effects and the potential role of warming in mitigating the effects of invasion.