Surface blebbing and membrane vesicle formation was observed in fresh cultures of F. columnare and during the revival process of starved cells similar to those reported in F. psychrophilum[26].

Although the role of bleb formation and release of membrane vesicles is not clear, it has been postulated they may play a role in host-pathogen interaction due to the high content of antigenic proteins present in F. psychrophilum membrane vesicles. Further studies on the role that these ultrastructures may play in F. columnare pathogenesis are needed. The typical learn more capsule described for F. columnare[5] and F. psychrophilum[14] was missing from our TEM images probably due to different sample preparation methods. It is likely that during sample preparation for TEM, the capsule or mucus layer observed by SEM was removed find more since we did not use a capsule stabilization protocol. Differences in cell culturability were observed between strains although those could not be correlated with their genetic group. The strains used in this study were choosen based on their genotype and source of isolation [15]. Strains ARS-1, ALG-00-530 and AL-02-36 behaved similarly throughout the experiment

and the numbers of coiled forms at 14 days were statistically identical. The initial length of the cells seemed not to influence the coiling process since both the shortest (ARS-1) and the longest (ALG-02-36) strains behaved similarly. In the type Nintedanib (BIBF 1120) strain ATCC 23643, coiled cells were covered by a matrix layer that made difficult to observe the cell structure in detail. SEM observations of starved ATCC 23643 cells resembled those described in starved Vibrio cholerae cells by Chaiyanan et al. [27] in where V. cholerae cells had remained viable for a 2-year period. The appearance of coiled cells covered by a matrix was also observed in strain ALG-00-530 after 5 months in ultrapure water. Cells were connected

by what appeared to be fimbriae, a characteristic structure that has also been reported in other long-term starvation studies [13, 27, 28]. Our results showed that strains of F. columnare followed a similar strategy to survive under lack on GSK2118436 nmr nutrients by adopting a coiled conformation and secreting a matrix layer, although this process occurred faster in some strains. Under starvation conditions and in absence of organic nutrients, F. columnare can survive for at least 5 months at ambient temperature in sterile water. In a previous study [10], the authors proposed that F. columnare survived the nutrient-deprived conditions by utilizing nutrients released from dead cells that allowed cultures to maintain constant growth over time. Our results contradict this assumption because in all our microscopic observations we failed to detect any cells undergoing cell division although we did note some lysed cells in our cell preparations that likely released nutrients into the medium. Based on our data, and at 5 months under starvation, more than 99% of the F.