Determination of Raman spectrum under different culture conditions: preliminary research on bacterial fish pathogens.

The intensive labour and time required for conventional methods to identify bacterial fish pathogens have revealed the need to develop alternative methods. Raman spectroscopy has been used in the rapid optical identification of bacterial pathogens in recent years as an alternative method in microbiology. Strains of bacterial fish pathogens (Vibrio anguillarum, Lactococcus garvieae and Yersinia ruckeri) that often cause infectious diseases in fish were here identified and analyzed in terms of their biochemical structures in different media and at different incubation times, and the data were specified by using Raman spectroscopy. The results demonstrated that Raman spectroscopy presents species-specific Raman spectra of each disease-causing bacteria and that it would be more appropriate to choose general microbiological media over selective media for routine studies. Additionally, it was found that species-specific band regions did not differ in 24- and 48-hour cultures, but there could be a difference in peak intensity which may lead to difficult characterization of spectrum. The current study, conducted for the first time with bacterial fish pathogens under different incubation conditions, is believed to provide a basis for the routine use of Raman spectroscopy for quick pathogen identification and the precise determination of the methodology for further research.

Mass mortality of the keratose sponge Sarcotragus foetidus in the Aegean Sea (Eastern Mediterranean) correlates with proliferation of Vibrio bacteria in the tissues.

In the last two decades, episodes of mass mortality in benthic communities have often been associated with climatic anomalies, but the ultimate mechanisms through which they lead to death have rarely been identified. This study reports a mass mortality of wild sponges in the Aegean Sea (Turkey, Eastern Mediterranean), which affected the keratose demosponge Sarcotragus foetidus in September 2021. We examined the occurrence of thermo-dependent bacteria of the genus Vibrio in the sponges, identified through 16S rRNA of colonies isolated from sponge tissue in specific culturing media. Six Vibrio sequences were identified from the sponges, three of them being putatively pathogenic (V. fortis, V. owensii, V. gigantis). Importantly, those Vibrios were isolated from only tissues of diseased sponges. In contrast, healthy individuals sampled in both summer and winter led to no Vibrio growth in laboratory cultures. A 50 years record of sea surface temperature (SST) data for the study area reveals a progressive increase in temperature from 1970 to 2021, with values above 24°C from May to September 2021, reaching an absolute historical maximum of 28.9°C in August 2021. We hypothesize that such elevated SST values maintained for several months in 2021 promoted proliferation of pathogenic Vibrio species (thermo-dependent bacteria) in S. foetidus, triggering or aggravating the course of sponge disease. Thus, vibrioisis emerges as one of the putative mechanisms through which global water warming in the Mediterranean Sea translates into sponge mortality. The historical time course of temperature data for the studied area in the Aegean Sea predicts that recurrent waves of elevated SST are likely to occur in the coming summers. If so, recurrent disease may eventually eliminate this abundant sponge from the sublittoral in the midterm, altering the original bathymetric distribution of the species and compromising its ecological role.

First preliminary study on identification of bacterial fish pathogens with Raman spectroscopy.

Accurate and rapid determination of bacterial disease agents of fish is an important step for sustainable and efficient aquaculture production. In general, biochemical and molecular methods are used for pathogen detection but they are usually time-consuming and required qualified personnel. Recently spectroscopic methods are preferred in clinical and food microbiology and declared as a promising alternative method for pathogens diagnosis with many advantages. In this study, the significant spectra of three important bacterial fish pathogens (Lactococcus garvieae, Vibrio anguillarum and Yersinia ruckeri) were determined by Raman spectroscopy. The first data of the pathogens were obtained and the distinctive differences in polysaccharides, nucleic acids, fatty acids and amino acids were identified. This preliminary study aimed to be pioneer for further studies in aquaculture and veterinary microbiology toward developing an alternative method for routine identification.