# Laminar _Ulva_ Species: A Multi-Tool for Humankind?
## 2 The Biology of _Ulva_ sp.
### Algae Microbial Interaction
Molecular ion imaging of the metabolites unveiled dynamic alterations in surface-associated compounds. An extensive dataset comprising spatially and temporally resolved compounds, including DMSP and 55 specific molecular biomarkers, facilitated the distinction of four distinct time points in the gametogenesis process [13,39]. [PERSON] et al. [39] explored whether the algae-bacteria relationship arose due to the mutual exploitation of common environmental signals. They subjected a sample of _Ulva_ to axenic conditions, leading to the development of callus-like structures resembling pincushion morphotypes. These structures were characterized by unusual cell wall formations, a lack of cell differentiation, and slow growth. Upon the introduction of two bacterial strains--_Rosevourius_ sp. and _Maribacter_ sp.--the morphogenesis of _Ulva compressa_ (formerly _U. mutabilis_) was fully restored, resulting in the formation of a tripartite community, as previously described in studies by [PERSON] et al., 2016 [65] and [PERSON] et al., 2012 [63,65, 39]. DMSP was then identified as an attractant and tracked from algal production to bacterial uptake, i.e., _Ulva_ releases significant amounts of DMSP into its chemosphere. _Rosevourius_ sp. are attracted to DMSP and absorb this metabolite quickly. Although they do not directly stimulate bacterial growth, once a specific threshold is reached, bacteria uptake and store more DMSP than _Ulva_ releases de novo. This leads to bacterial biofilm expansion as _Ulva_ provides a boundary layer of glycerol, serving as a carbon source for _Rosevourius_ sp. Additionally, chemical communication can occur bidirectionally; bacteria can attract _Ulva_ zoospores using N-acyl homoserine lactones, as reported by [PERSON] et al., 2007 [66]. Upon initial interactions, morphogenetic compounds trigger cell division in _Ulva_ (_Rosevourius_ factor) and rhizoid formation (_Maribacter_ factor). These morphogenetic compounds overall promote biomass production and facilitate the formation of retention structures, allowing algae to integrate directly into the bacterial biofilm [39,66]. We can therefore say, taking into account the various examples described above, that bacteria are essential and play a crucial role in the physiology of _Ulva_ sp. from development and growth to the induction of reproduction, sporulation, and the settlement of its zoospores through various mechanisms, such as production of growth-promoting substances, quorum sensing, signaling mediated by bioactive compounds, etc. [54]. To this end, _Ulva_ sp. needs to cultivate bacteria that create protective biofilms around rhizoid cells and provide morphogens for their growth (Figure 2). Furthermore, they also release various organic compounds into their environment to harm other organisms and to maintain the balance of osmotic pressure in the surrounding seawater [39]. Because bacteria can selectively utilize nutrients from algae, they play a key role in biotransformation and nutrient recycling [54]. However, on the other hand, we can also find epiphytes. Epiphytic individuals can be other unwanted species of algae, viruses, bacteria, and fungi. They can attract herbivores such as crabs, lobsters, shrimps, crayfish, fish, and turtles, which have positive (enriched biodiversity throughout the food chain, ecosystem services, etc.) and negative (loss of yield, etc.) impacts on seaweed cultivation [67]. According to [PERSON] et. al. 2010 [68], epiphytic bacteria also provide a defensive function through their antibiotic activity or by forcing pathogenic bacteria to compete for space within the biofilm [47,54].