Mak­ing a Liv­ing in the Nu­cleus

Note­wor­thy

When it comes to in­tra­cel­lu­lar pathogens, we usu­ally think of those that re­main in­side a mem­brane-en­closed vac­uole and those that es­cape into the cy­to­plasm. Much rarer are cases of par­a­site that make a liv­ing in­side the nu­cleus. Makes sense, en­ter­ing the space where the DNA re­sides is likely coun­ter­pro­duc­tive as it could eas­ily trig­ger apop­to­sis (pro­grammed cell death). Fast death of the in­fected host cell would serve to limit the in­fec­tion. But, per­haps not sur­pris­ingly, some bac­te­ria have found the way to make a liv­ing in the nu­cleus.

A sin­gle 'Ca. En­donu­cle­obac­ter' in­fects the mus­sel nu­cleus (early in­fec­tion stage), grows through elon­ga­tion and di­vi­sion (mid-in­fec­tion stage), and fi­nally di­vides through sep­ta­tion of the elon­gated cells to as many as 80,000 cells (late in­fec­tion stage). In the fi­nal in­fec­tion stage, the nu­cleus is en­larged by as much as 50-fold in vol­ume, the host cell bursts and the par­a­sites are re­leased to the en­vi­ron­ment. a, 'Ca. En­donu­cle­obac­ter' in­fec­tious cy­cle in the early, mid and late stages of in­fec­tion, shown in the left, mid­dle and right columns, re­spec­tively, of the top row (mid­dle row, FISH im­ages of 'Ca. E. puteoser­pen­tis'; bot­tom row, TEM im­ages of 'Ca. E. chil­dressi'). FISH with spe­cific probes shows the par­a­site (in yel­low) in­side mus­sel nu­clei (DAPI-stained DNA in blue) and neigh­bour­ing sym­biont-con­tain­ing cells (in­di­cated with dot­ted lines) with sul­fur-ox­i­diz­ing sym­bionts (in green) and methane-ox­i­diz­ing sym­bionts (in pink) (se­quences of all FISH probes are listed in Sup­ple­men­tary Ta­ble 6). e, 'Ca. En­donu­cle­obac­ter' cell; c, chro­matin; ne, nu­clear en­ve­lope. The re­sults are rep­re­sen­ta­tive of five in­de­pen­dent ex­per­i­ments. Scale bars, 1 μm. Source

One such clever nu­clear in­vader in­fects mus­sels that re­sides in the vicin­ity deep ocean vents and is known as "Ca. En­donu­cle­obac­ter" (Ca. since it has yet to be cul­tured.) In a re­cent pub­li­ca­tion the au­thors show just how a sin­gle cell that reaches the nu­cleus can lead to >80,000 prog­eny cells be­fore caus­ing ma­jor nu­clear dam­age. It's se­cret? It doesn't even try to eat the DNA or RNA. Rather, it ex­press im­porters for nu­tri­ents such as sug­ars, lipids, amino acids and mucin. And it se­cretes apop­to­sis in­hibitors! Strik­ingly, the genes that en­code these in­hibitors in the bac­terium orig­i­nally came from the host, via eu­kary­ote-to-bac­te­ria hor­i­zon­tal gene trans­fer. You should dive deep into this fas­ci­nat­ing pa­per. (See the pa­per for fig­ure ex­pla­na­tion.)

Our 2018 piece The Nu­clear Op­tion men­tioned"Ca. En­donu­cle­obac­ter" al­ready, be­sides other bac­te­ria that pur­sue this un­usual lifestyle.
 

 

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