Combined collapse by bridging and self-adhesion in a prototypical polymer model inspired by the bacterial nucleoid

Recent experimental results suggest that the E. coli chromosome feels a self-attracting interaction of osmotic origin{,} and is condensed in foci by bridging interactions. Motivated by these findings{,} we explore a generic modeling framework combining solely these two ingredients{,} in order to characterize their joint effects. Specifically{,} we study a simple polymer physics computational model with weak ubiquitous short-ranged self attraction and stronger sparse bridging interactions. Combining theoretical arguments and simulations{,} we study the general phenomenology of polymer collapse induced by these dual contributions{,} in the case of regularly spaced bridging. Our results distinguish a regime of classical Flory-like coil-globule collapse dictated by the interplay of excluded volume and attractive energy and a switch-like collapse where bridging interactions compete with entropy loss terms from the looped arms of a star-like rosette. Additionally{,} we show that bridging can induce stable compartmentalized domains. In these configurations{,} different {"}cores{"} of bridging proteins are kept separated by star-like polymer loops in an entropically favorable multi-domain configuration{,} with a mechanism that parallels micellar polysoaps. Such compartmentalized domains are stable{,} and do not need any intra-specific interactions driving their segregation. Domains can be stable also in the presence of uniform attraction{,} as long as the uniform collapse is above its theta point.