The anchoring and mooring of boats mechanically damage Posidonia oceanica plants; however, no information is available on the effect of this kind of damage on the plant holobiont, i.e., on the associated bacterial and fungal communities. Indeed, bacterial communities are known to change under different plant stress conditions but the dynamics of seagrass-associated fungi remain largely unexplored. We used DNA metabarcoding to profile the bacterial and fungal colonizers of two nearby P. oceanica patches in the Villefranche-sur-Mer bay (France) differing by the amount of exposure to mechanical stress due to boat transit and anchoring. Bacterial communities showed a significant reduction in diversity with an increase in Vibrio sp. in the rhizome and root samples from the impacted site, where the accumulation of dead organic material favors opportunistic heterotrophs. Conversely, fungal communities showed increased diversity in the leaf samples from the impacted site, where a reduction in the dominant P. oceanica host-specific mutualistic endosymbiont, Posidoniomyces atricolor, was found. This change was probably due to the opening up of new colonizable niches for several fungal species. Although this study represents a preliminary assessment of the effect of mechanical stresses on P. oceanica-associated microbial communities, it further supports their putative use as a seagrass descriptor.

Wastewaters from household appliances, such as dishwashers and washing machines, are an untapped resource of recoverable water and/or nutrients. The Zero Mile system has been developed to reuse/upcycle dishwasher wastewaters through bioremediation activity carried out by an ad hoc engineered phototrophic/heterotrophic microbial consortium. The choice of both suitable microorganisms for engineering consortia and detailed knowledge on their structure, behaviour and interaction are essential to optimising consortium culture conditions and drive the biofilter container design (structure and topology). To these aims, the effect of abiotic conditions (i.e., irradiance, pH and organic load) on the microbial consortium growth and its capability to survive and thrive in different dishwasher wastewater dilutions have been evaluated. At the same time, the crucial interplay between biological and design research has allowed us to define the characteristics of the biofilter container and plan its development for the industrial application of the Zero Mile system, bringing sustainability benefits as it moves household wastewater from a traditional linear model to a more sustainable, circular approach.

The crucial role of plant–microbe interactions in seagrass growth and overall fitness is widely recognized and known to influence plant response to stress. Human-induced changes in coastal ecosystems necessitate efficient descriptors for seagrass monitoring. Recently, for Posidonia oceanica meadows, an integrative approach combining ecophysiological descriptors with bacterial communities has been successfully applied. Conversely, the mycobiota remains largely unexplored and fungal communities cannot be included yet as a putative descriptor. This study aims to evaluate the ecological status of two P. oceanica meadows in the Akrotiri Bay (Cyprus), located under different geomorphological features (depth and seabed type) and degrees of human pressure (port proximity vs. Marine Protected Area). A set of descriptors including morphometry, biochemical markers and bacterial communities collected in 2023 are compared with those collected, at the same sites, in 2017. Furthermore, the investigation of the leaf-associated microbial community included the underrepresented fungal communities, in addition to the bacterial ones, to evaluate their usefulness in evaluating the plant conservation status. Results indicated a good P. oceanica conservation status at both sites, showing an amelioration in the Limassol port meadow from 2017. In 2023, the biometrical/biochemical descriptors were found comparable across sites as the bacterial communities, differing from 2017 results. Noteworthy, fungal communities exhibited significant differences between sites, with a clear reduction, in the Limassol port meadow, of the dominant Posidoniomyces atricolor which is known as a specific colonizer of P. oceanica roots. These results confirm the strong relationship between P. atricolor and P. oceanica host, and suggest its sensitivity to environmental changes, able to keep track of ecological shifts.