Loss of Motility as a Non-Lethal Mechanism for Intercolony Inhibition (“Sibling Rivalry”) in Marinobacter

Abstract

Bacteria from the genus Marinobacter are ubiquitous throughout the worlds’ oceans as “opportunitrophs” capable of surviving a wide range of conditions, including colonization of surfaces of marine snow and algae. To prevent too many bacteria from occupying this ecological niche simultaneously, some sort of population dependent control must be operative. Here, we show that while Marinobacter do not produce or utilize an acylhomoserine lactone (AHL)-based quorum sensing system, “sibling” colonies of many species of Marinobacter exhibit a form of non-lethal chemical communication that prevents colonies from overrunning each other’s niche space. Evidence suggests that this inhibition is the result of a loss in motility for cells at the colony interfaces. Although not the signal itself, we have identified a protein, glycerophosphoryl diester phosphodiesterase, that is enriched in the inhibition zone between the spreading colonies that may be part of the overall response.

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“…The cells in freshly populated space displayed higher activity due to distance from established populations. A similar decrease in motility and respiration was observed during the study of sibling rivalry in M. algicola [25]. Bacteria, in general, spread outward for constant supply of a better nutritional environment [48].…”

“…To determine whether colony arrest was due to death of cells, we stained colonies by flooding plates with , BacLight (Molecular Probes; Kit L13152) [25], and viewed fluorescence after 15 min using a fluorescence stereomicroscope (Olympus SZX16). Images obtained using GFP and RFP filters were composited in ImageJ.…”

“…Images obtained using GFP and RFP filters were composited in ImageJ. To assess the respiratory activity of the cells across the colony, we conducted the TTC (2,3,5-triphenyltetrazolium chloride) assay [25]. In brief, a 0.01% TTC (MP Biomedicals, LLC, SR00767) solution was prepared in water, and 5 ml was poured over 10-day-old swimming colonies.…”

“…B. subtilis was capable of forming swarming colony boundaries with less phylogenetically related soil isolates, and the isolates that exhibited boundary formation were also reported to compete for root surface colonization [23]. While kin rivalry between nonidentical strains is well established, isogenic strains of swimming Marinobacter algicola, and Pseudomonas putida and swarming Paenibacillus dendritiformis have been reported to develop a boundary between two colonies, termed sibling rivalry [25; 26; 27; 28]. Recently, Kastrat and Cheng reported inhibition within and across Escherichia coli strains and other bacteria [28].…”

“…In P. dendritiformis , subtilisin, a lethal protein that regulates colony density, is secreted at higher cell density, resulting in the development of a demarcation line between the two swarming colonies [29]. M. algicola arrest in swimming populations has been linked to the protein glycerophosphoryl diester phosphodiesterase (GDPD), but its role in this process remains unclear [25]. No chemical compounds were detected in the case of P. putida, where compression waves among opposing colonies cause the development of the demarcation line [27].…”