I guess nobody did this kind of studies since there are 2 taxonomically ordinary species of thousands described. E.coli - is belonging to gamma-proteo, R.rubrum to alpha-proteo - different classes (actually different phyla). You can try to find something about phylogeny of Proteobacteria...

You can find a phylogenetic comparison of all Proteeobacteria using a procedure described in this paper. This will give you the relative placement of the two organisms taxonomically but it may not add much to what the two previous posters said about them being distantly related Proteobacteria species.

http://www.nature.com/srep/2013/130618/srep02015/full/srep02015.html

The interactive tree is here:

http://supfam.cs.bris.ac.uk/SUPERFAMILY/cgi-bin/createtree.cgi?treeformat=svg&genomes=6C,gH,aB,zLb,mTp,dH,6k,00,4I,3y,6x,05,Ugv,35,9LF,eE,lH,lJ,ws,OhS,Of8,hh,9T,jJ,OtX,hl,1X,1d,1t,dI,nno,bd,iY,yt,HM0,0l,cM,dp,iU,9l,3W,dX,2K,6D,ln,6bi,5K,hO,ds,0t,3F,0V,Hwc,f3,3c,p8,5Z,1G,3g,9z,jw,N7y,gm,lar,aE,60,55,4N,jX,xdJ,m1,c8R,8B,bD,az,H1n,dj,5A,85A,0q,gDN,0N,vi,0I,19,hL,9f,bB,1W,lE,4R,m7,nt,aaP,0E,tSr,LTy,14,VqB,bS,ZlY,7i,rl,9x,r4,GpG,2j,yp2,2Z,bY,WJv,0s,rad,aI,eK,ku,90,b5,20,1m,0u,5l,76,30,b4,eM,2Y,4b,iV,i6w,eI,7d,p6,01,2B,rx,0U,rdl,43,4t,f5,fR,dW,5e,xWE,4d,bI,gN,lyO,RHK,kG,5y,9k,be,bp,bo,dY,QfE,nl,dJw,3j,ne,53,bA,hC,dC,7o,3B,8A,kk,ey,ak,fU,nv,7eu,9t,g4,K9J,2i,8I,2x,5W,54,6q,qab,hMi,ja,ic,sg,iB,RWa,mdV,2r,21,6N,27,SjQ,m5,kg,iNa,iFE,mbz,9R,mV3,NUH,3m,7c,lK,hT,ox,1S,fQ,WVw,9W,o3R,nCh,jH,tJN,nc,0T,9q,5T,eg,el,ea,as,0C,9D,2q,6i,6h,rt,jkW,jgR,jHX,0W,rf,uzJ,jTT,6a,jIh,2C,kEc,jOP,tNr,ioy,74,6b,rc,cV,2d,75,j5,4G,7s,fj,6G,7w,1e,1K,40,1Y,rHr,6z,6g,1E,1k,91,1T,2m,gW,5xG,9p,17,au,0Y,kW,5C,3Z,0p,VuP,iA,mk,ke,8q,fFw,fC,ROp,bZ,dZF,5k,wi,nb,bj,26,QyB,6u,gM,ho,4K,bq,4c,lWv,lUM,ki,3L,7S,5q,dP,f8B,km,hd,O15,4f,4k,1c,dYy,3M,iQ,44,33,k1,f4,65,vp,8W,a4f,kn,xF0,hY,15,he,0x,UXe,il,eY,h5,1r,8l,6d,hw,6t,sl,1a,88,0f,2p,7H,3w,2a,lw,eX,px,ha,2O,d0,fV,NIj,VgN,hjd,Vhd,1n,kM,kb,hc,4H,2b,fL,0z,kP,5s,c8,hR,WIr,gV,mt,3i,hNM,gC,hry,Mbo,9i,7m,xc,6R,ju,jy,8R,QK3,5r,4S,7T,3b,9G,88C,dE,aJ,nr,2n,8Q,2w,b1,bO,5i,5f,JKN,tJo,6Z,GiE,9U,3I,5J,TDt,2S,ck,eUc,4ut,7M,er,1A,og,eG,eT,9Y,wb,iT,hky,3o,3K,pd,0O,8M,06,5h,1g,7B,bQ,on,3s,d1,ez,hG,jvn,wF9,V29,7e,sAr,5B,fyM,jn,8V,2A,Rgo,kd,0K,ej,J3k,dJ,7R,8H,DnW,08,INE,IQ5,IEC,8Y,5x,4W,hKM,w6D,hQ,pq,pj,2e,fP,0a,qf,4T,4y,2t,Wbb,9m,w32,1v,ri,pz,dL,aU,lnz,1l,ab,fO,WNl,YkC,tc,MJr,MXK,8p,3a,MBl,0b