From the cultures of Photobacterium damselae subsp. piscicida, the aetiological agent of fish pasteurellosis, a new siderophore named piscibactin (1), was isolated as its gallium and iron(III) complexes along with a possible intermediate of its biosynthesis, prepiscibactin (2). Analysis of the gene cluster involved in the siderophore biosynthesis allowed the partial prediction of the structures. Thus, an NRPS‐mediated mechanism similar to that for yersiniabactin was suggested by protein sequence comparisons. The final structures were solved by NMR and MS methods and by DFT molecular modeling. The results obtained in the structural and functional characterization of piscibactin enabled the proposal of a biosynthetic pathway.

The iron uptake mechanisms based on siderophore synthesis used by the fish pathogen Aeromonas salmonicida subsp. salmonicida are still not completely understood, and the precise structure of the siderophore(s) is unknown. The analysis of genome sequences revealed that this bacterium possesses two gene clusters putatively involved in the synthesis of siderophores. One cluster is a candidate to encode the synthesis of acinetobactin, the siderophore of the human pathogen Acinetobacter baumannii, while the second cluster shows high similarity to the genes encoding amonabactin synthesis in Aeromonas hydrophila. Using a combination of genomic analysis, mutagenesis, biological assays, chemical purification, and structural determination procedures, here we demonstrate that most A. salmonicida subsp. salmonicida strains produce simultaneously the two siderophores, acinetobactin and amonabactin. Interestingly, the synthesis of both siderophores relies on a single copy of the genes encoding the synthesis of the catechol moiety (2,3-dihydroxybenzoic acid) and on one encoding a phosphopantetheinyl transferase. These genes are present only in the amonabactin cluster, and a single mutation in any of them abolishes production of both siderophores. We could also demonstrate that some strains, isolated from fish raised in seawater, produce only acinetobactin since they present a deletion in the amonabactin biosynthesis gene amoG. Our study represents the first evidence of simultaneous production of acinetobactin and amonabactin by a bacterial pathogen and reveals the plasticity of bacterial genomes and biosynthetic pathways. The fact that the same siderophore is produced by unrelated pathogens highlights the importance of these systems and their interchangeability between different bacteria.

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The benefits of homework on student learning and academic achievement, to a large extent, depend on the degree of student engagement. Motivational engagement (my intention or why I do the homework), cognitive engagement (how I get involved in homework), and behavioral engagement (how much homework I do, how much time I devote to it, how I manage that time) are key aspects that condition the quality of the process of doing homework, learning, and academic achievement. Prior academic achievement is one of the variables that seems to be positively related to student engagement (both due its motivational component and to the training to do homework). The main purpose of this work was to study in detail this relationship in students of the last stage of Primary Education (N = 516). The results showed that (i) as achievement levels rise, the use of a shallow focus to doing homework decreases (and the use of a deep approach increases); (ii) there is also a progressive increase in the amount of homework done and in the management of the time dedicated to homework. On another hand, as in previous research, (iii) no relationship was observed between the levels of prior achievement and the amount of time spent doing homework.

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