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A critical challenge during volcanic emergencies is responding to rapid changes in eruptive behaviour. Actionable advice, essential in times of rising uncertainty, demands the rapid synthesis and communication of multiple datasets with prognoses. The 2020-2021 eruption of La Soufrière volcano exemplifies these challenges: a series of explosions from 9-22 April 2021 was preceded by three months of effusive activity, which commenced with a remarkably low level of detected unrest. Here we show how the development of an evolving conceptual model, and the expression of uncertainties via both elicitation and scenarios associated with this model, were key to anticipating this transition. This not only required input from multiple monitoring datasets but contextualisation via state-of-the-art hazard assessments, and evidence-based knowledge of critical decision-making timescales and community needs. In addition, we share strategies employed as a consequence of constraints on recognising and responding to eruptive transitions in a resource-constrained setting, which may guide similarly challenged volcano observatories worldwide.

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The GlgE pathway is thought to be responsible for the conversion of trehalose into a glycogen-like α-glucan polymer in bacteria. Trehalose is first converted to maltose, which is phosphorylated by maltose kinase Pep2 to give α-maltose 1-phosphate. This is the donor substrate of the maltosyl transferase GlgE that is known to extend α-1,4-linked maltooligosaccharides, which are thought to be branched with α-1,6 linkages. The genome of Streptomyces venezuelae contains all the genes coding for the GlgE pathway enzymes but none of those of related pathways, including glgC and glgA of the glycogen pathway. This provides an opportunity to study the GlgE pathway in isolation. The genes of the GlgE pathway were upregulated at the onset of sporulation, consistent with the known timing of α-glucan deposition. A constructed ΔglgE null mutant strain was viable but showed a delayed developmental phenotype when grown on maltose, giving less cell mass and delayed sporulation. Pre-spore cells and spores of the mutant were frequently double the length of those of the wild-type, implying impaired cross-wall formation, and spores showed reduced tolerance to stress. The mutant accumulated α-maltose 1-phosphate and maltose but no α-glucan. Therefore, the GlgE pathway is necessary and sufficient for polymer biosynthesis. Growth of the ΔglgE mutant on galactose and that of a Δpep2 mutant on maltose were analysed. In both cases, neither accumulation of α-maltose 1-phosphate/α-glucan nor a developmental delay was observed. Thus, high levels of α-maltose 1-phosphate are responsible for the developmental phenotype of the ΔglgE mutant, rather than the lack of α-glucan.

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The potential of NIS spectroscopy to study the iron-sulfur clusters in metalloproteins is illustrated using model compounds. The origin of the intense low energy transfer bands is discussed.