## 1 Introduction  
_Marinobacter_ belong to the class of \(\gamma\)-proteobacteria and these motile, halophilic, or halotolearnt bacteria all share the ability to use petroleum hydrocarbons as their sole energy and carbon sources [1]. Numerous strains of _Marinobacter_ have been described from ecological niches as diverse as high-latitude seawater and Antarctic sea ice [2; 3; 4], hypersaline mats [5; 6], oil-producing wells [7], oil-contaminated marine sediments [8], and even marine sponges [9]. In addition, this genus is often found in association with phytoplankton [10; 11; 12; 13; 14; 15]. Because of its wide ecological distribution, the _Marinobacter_ genus is ubiquitous in the ocean and its species can be described as \"opportuninprobs\" able to survive under a wide-range of conditions [16]. While _Marinobacter_ spp. account numerically for only a small proportion of the total bacteria present in the \"phycosphere\" of algae-associated environments, either in culture or in the field [17], they are almost always present in the core microbiome of phytoplankton in general and dinoflagellates in particular [10; 18; 19; 20; 21]. Thus, they appear to be a \"keystone\" taxon that may modulate the physiology of the host via iron acquisition through the secretion of iron siderophores [22], inducing cell aggregation [23; 24], or excystment through the release of growth factors [25; 26]. Although many potentially algal-associated bacteria occur in seawater, it is perhaps surprising that in general only a few individuals, on average 1.8-2.3 [18; 27], actually colonize the surface of a phytoplankton host at the same time, suggesting a possible intraspecies competition for this niche. In a more general sense, all bacterial communities compete for resources and niche space. This would include colonization of algal surfaces as part of various types of bacterial-algal interactions. Thus, there must be various ways that bacteria and/or algae can control the colonizing population of an algal surface, most of which likely invoke some sort of cell-to-cell communication. Indeed, previous studies have demonstrated that cell-to-cell communication across populations is concentrated within marine microhabitats such as biofilms, marine snow, and eukaryotic co-associations [28]. Currently the most well-studied and best-understood mechanism of bacterial communication is quorum sensing based on N-acyl homoserine lactone (AHL) signaling, which is utilized by Gram-negative bacteria within the alpha-, beta-, and \(\gamma\)-proteobacteria classes [29]. Cells within individual populations synthesize diffusible AHL molecules, the concentration of which increases proportionally with increasing population density until a critical threshold concentration is reached, at which time the AHL binds to receptor proteins responsible for the transcription and subsequent expression of target genes encoding for a particular phenotype [29; 30]. Quorum sensing dependent phenotypes include antibiotic production, biofilm formation, production of virulence factors, and swarming motility [28; 30; 31]. These behaviors are particularly important for successful colonization of higher organisms by opportunistic pathogens such as _Pseudomonas aeruginosa_ and _Vibrio harvest_[32]. The _Marinobacter_ group is phylogenetically similar to _Pseudomonas_[7; 33], however, there is only limited evidence that _Marinobacter_ are capable of producing AHLs [34; 35]. Thus, it is presently unknown whether AHL synthesis or utilization is a general characteristic of the genus. A parallel approach to controlling population density in bacterial communities is through the excretion of cell-to-cell signals that function as \"no trespassing\" or \"no-go zone\" signs such as bacteriocins [36]. Bacteriocins are biologically active small peptides or protein complexes that display an alleopathic or bactericidal mode of action towards the same or closely related species [37] and have been found in all major lineages of bacteria [38].