In this Rapid Communication, we have examined the superconducting ground state of the HfV2Ga4 compound using resistivity, magnetization, zero-field (ZF), and transverse-field (TF) muon-spin relaxation and rotation (μSR) measurements. Resistivity and magnetization unveil the onset of bulk superconductivity with TC∼3.9 K. TF-μSR measurements show the temperature dependence of the superfluid density, indicating, surprisingly, a nodal two-gap s+d-wave superconducting order parameter. In addition, the ZF muon relaxation rate increases with decreasing temperature below 4.6 K, suggesting the presence of weak spin fluctuations. These observations pointed to an unconventional multiband nature of the superconducting ground state. To better understand these findings, we carry out first-principles electronic-structure calculations, further highlighting multiple disconnected sheets with very different orbital weights and spin-orbit coupling composing the Fermi surface, bridging the way for a nodal multiband superconductivity scenario. In this vein, therefore, the HfV2Ga4 family stands out as an open avenue to novel unexplored unconventional superconducting compounds and an ideal playground to investigate the mechanisms behind such phenomena.

Background: A central theme in (micro)biology is understanding the molecular basis of fitness i.e. which strategies are successful under which conditions; how do organisms implement such strategies at the molecular level; and which constraints shape the trade-offs between alternative strategies. Highly standardized microbial laboratory evolution experiments are ideally suited to approach these questions. For example, prolonged chemostats provide a constant environment in which the growth rate can be set, and the adaptive process of the organism to such environment can be subsequently characterized. Results: We performed parallel laboratory evolution of Lactococcus lactis in chemostats varying the quantitative value of the selective pressure by imposing two different growth rates. A mutation in one specific amino acid residue of the global transcriptional regulator of carbon metabolism, CcpA, was selected in all of the evolution experiments performed. We subsequently showed that this mutation confers predictable fitness improvements at other glucose-limited growth rates as well. In silico protein structural analysis of wild type and evolved CcpA, as well as biochemical and phenotypic assays, provided the underpinning molecular mechanisms that resulted in the specific reprogramming favored in constant environments. Conclusion: This study provides a comprehensive understanding of a case of microbial evolution and hints at the wide dynamic range that a single fitness-enhancing mutation may display. It demonstrates how the modulation of a pleiotropic regulator can be used by cells to improve one trait while simultaneously work around other limiting constraints, by fine-tuning the expression of a wide range of cellular processes.