Supplemental Information Supplemental Text Math for back calculating the per-cell division rates in Henson et al. 2018 assuming 15%--55% viability. "# Denote the initial cell count as �!, and the cell count in � generation as�$. If all the cells are viable, per each generation, all the cells are doubling: �$ = �$%& ⋅ 2 (eq. S1.1) And therefore, after �generations, the cell count �$would be: $ �$ = �! ⋅ 2 (eq. S1.2) When not all the cells are viable, for each generation, instead of simply doubling the whole population, only a portion of the cells (denoted as� < 1) replicates. In this case: �$ = �$%& ⋅ (1 + �) (eq. S1.3) Here we can see that (eq. 3.1) is actually a special case of (eq. 3.3), when � = 1, �$ = �$%& ⋅ (1 + 1) = �$%& ⋅ 2 When � < 1, after � generations: $ �$ = �! ⋅ (1 + �) (eq. S1.4) Denoting the total time to get � generations as �, which means the number of generations per unit time, also known as the per-cell division rate, is � = �/�. Rewriting (eq. 3.4), we have: '⋅" '⋅)*+!(&-.)⋅" �$ = �! ⋅ (1 + �) = �! ⋅ 2 (eq. S1.5) According to (eq. 3.5), a cell population of �viability and � per cell division rate, the population division rate is: �0*01)2"3*$ = � ⋅ ���4(1 + �) (eq. S1.6) %& Henson et al. 2018 show that the optimal population division rate of SAR11 LD12 is �0*01)2"3*$ = 0.5 ��� , assuming the viability of LD12 is � = 0.15, by plugging in these two numbers to (eq. S1.6), we can get the per-cell division rate of LD12 is: � = �0*01)2"3*$/���4(1 + �) %& = 0.5 ��� /���4(1 + 0.15) = 0.5 ���%&/0.20163 = 2.48 ���%& If assuming � = 0.55, � = 0.79 ���%&. Therefore, given the range of the viability of LD12 is between 15%-- 55%, the corresponding per cell division rate is between 0.79 divisions to 2.48 divisions per day. Supplemental Table Supplemental Table S1 is a spreadsheet, Table_S1.xlsx. This includes MWH media recipes, ASV and OTU tables, taxonomic and relative abundance information for all isolates, NMDS information, biogeochemical data for the samples, and the BLAST results of isolate hits. Available at https://doi.org/10.6084/m9.figshare.12142113. Supplemental Figures follow, with captions embedded gi 1434172709 gb MH671546 1 Terrabacter sp strain Actino-50 98 gi 260150789 gb GQ369088 1 Terrabacter sp Z0-YC6820 76 Figure S1 98 gi 322184102 gb JF198697 1 Uncultured bacterium clone ncd2318c07c1 gi 1434172666 gb MH671503 1 Terrabacter sp strain Actino-6 95 gi 1219688315 gb MF526112 1 Terracoccus sp strain MadaFrogSkinBac DB 2810 93 9377 gi 929046992 gb KR010185 1 Terrabacter terrae strain NSB-36 8295 7896gi 1219687689 gb MF525486 1 Terracoccus sp strain MadaFrogSkinBac DB 3694 95 96 gi 33309345 gb AF408945 1 Terrabacter sp Ellin103 96 gi 675399428 gb KJ878630 1 Terrabacter sp ES3-48 95 93 gi 984880284 emb LN876372 2 Terrabacter sp URHB0043 94 gi 984880215 emb LN876345 1 Terrabacter sp URHB0013 gi 1056940501 gb KX753012 1 Uncultured bacterium clone VLK 16 gi 411023858 gb JQ376619 2 Uncultured bacterium clone W031c9 11143 gi 636560307 ref NR 116367 1 Terrabacter aeriphilus strain 5414T-18 gi 109391678 gb DQ643663 1 Uncultured soil bacterium clone W4Ba03 gi 375244974 gb JQ625316 1 Uncultured bacterium clone OLH168 54 93 100 gi 381138672 gb JQ782930 1 Terrabacter sp 8-140 gi 166202141 gb EU262306 1 Uncultured bacterium clone 2005-MA-2-100207 gi 399762847 gb JX079240 1 Uncultured Terrabacter sp clone BG2-162 gi 226816208 dbj D84624 2 Phycicoccus sp S23430 92 gi 984880275 emb LN876406 1 Phycicoccus sp URHC0019 92 96gi 307593624 gb HM049681 1 Uncultured bacterium clone SZS-0 6 76 90 gi 359815377 emb FR853183 1 Uncultured bacterium 68 LSUCC0193 86 gi 38195153 gb AY360576 1 Uncultured actinobacterium clone H5Ba24 91 gi 636560657 ref NR 116717 1 Phycicoccus cremeus strain V2M29 Phycicococcus sp. 97 100 gi 9944265 emb AJ277696 1 Uncultured bacterium ARFS-29 partial gi 1341394009 ref NR 153681 1 Phycicoccus ginsengisoli strain DCY87 91 gi 356032913 gb GQ344406 2 Phycicoccus ochangensis strain B5a-b5 gi 1146076795 gb KY012263 1 Phycicoccus ginsenosidimutans strain AS4-17 99 gi 511194379 gb KC554448 1 Uncultured bacterium clone 8-586 100 gi 341925932 dbj AB649010 1 Phycicoccus aerophilus gi 327342252 gb JF417737 1 Uncultured bacterium clone QQSB18 96 gi 902940936 gb KP639140 1 Phycicoccus sp LZB055 72 81 99 gi 322184042 gb JF198637 1 Uncultured bacterium clone ncd2317b12c1 66 88 53 gi 511201697 gb KC606872 1 Uncultured bacterium clone CSbiofilm 18 040210 G04 68 gi 627529353 gb KJ473526 1 Uncultured Tetrasphaera sp clone BB32 46 gi 322160805 gb JF175399 1 Uncultured bacterium clone ncd2025g03c1 46 gi 1066599747 gb KX858544 1 Uncultured bacterium isolate DGGE gel band b1 93 gi 162137989 gb EU298817 1 Uncultured Tetrasphaera sp clone GASP-KB3W1 D12 100 gi 1124890878 gb KY386418 1 Knoellia sp strain R-68061 82 gi 1150392589 gb KY176950 1 Tetrasphaera sp strain S512 66 gi 1150392751 gb KY445722 1 Tetrasphaera sp strain TM-S120 68 gi 1150392586 gb KY176947 1 Tetrasphaera sp strain S405 gi 1434131666 gb MG594811 1 Janibacter hoylei strain O18 93 gi 928195899 gb KR054059 1 Janibacter cremeus strain HB45 93 gi 1189442627 gb KY775504 1 Janibacter anophelis strain IC B3 2 90 gi 918464473 gb KT382393 1 Bacterium BEL B20 24 79 gi 322211313 gb JF225908 1 Uncultured bacterium clone ncd2570c07c1 100 gi 322211930 gb JF226525 1 Uncultured bacterium clone ncd2581c01c1 10066 gi 643406902 gb KF086612 1 Uncultured bacterium clone ncm23c02c1 gi 1434172683 gb MH671520 1 Janibacter sp strain Actino-23 55 20 gi 27497666 gb AY167846 1 Janibacter limosus strain SAFR-043 74 98gi 595250671 gb KJ000756 1 Janibacter sp SCU-B24 gi 498905833 gb KC195789 1 Janibacter sp AB7 100 gi 1261504570 gb MG205908 1 Janibacter terrae strain NIOER183 25 99gi 498905834 gb KC195790 1 Janibacter sp AB9 98 83 gi 363991874 gb JQ014316 1 Janibacter sp LC420 gi 826022232 gb KP345928 1 Janibacter sp 3329 gi 221706541 gb FJ595986 1 Janibacter sp LI-80 19LSUCC0537 12gi 1287453529 dbj LC338047 1 Janibacter sp ASH66 29 Janibacter sp. 99gi 725096926 gb KM253202 1 Janibacter sp UR 2-02 gi 190364966 gb EU730944 1 Janibacter anophelis strain 221 24 gi 643428046 gb KF107716 1 Uncultured bacterium clone ncm61d02c1 100 gi 116871391 gb EF028236 1 Tetrasphaera remsis strain 3-M5-R-7 72 gi 636559739 ref NR 115799 1 Tetrasphaera remsis strain 3-M5-R-4 100 gi 238331493 gb GQ095316 1 Uncultured bacterium clone nbw437a10c1 gi 1219688047 gb MF525844 1 Intrasporangium calvum strain MadaFrogSkinBac DB 2536 100 gi 846386474 gb KR856422 1 Intrasporangium mesophilum strain SG66 gi 1185542091 emb LT631758 1 Micrococcus luteus LSUCC0042 17gi 330717791 gb JF792083 1 Micrococcus yunnanensis strain 17D 86 55gi 441090801 gb KC203087 1 Micrococcus sp WY22 55 53 gi 1388592975 gb MF093190 1 Micrococcus luteus strain B8 Micrococcus sp. 100 gi 493664540 emb HF952653 1 Micrococcus luteus gi 728852048 gb KJ544037 1 Bacterium AM0325 gi 826022277 gb KP345973 1 Micrococcus sp 3738 gi 1041571625 gb KX097063 1 Micrococcus sp A1S138 gi 194475415 gb EU861822 1 Uncultured soil bacterium clone A07 bac con 96 gi 8017974 emb AJ244799 1 Gram-positive bacteria SOGA22 gi 223034390 gb FJ354115 1 Uncultured bacterium clone L73 ML 217 53 gi 940373643 gb JX193447 2 Uncultured bacterium clone Q31020 100 100 gi 223030234 gb FJ349959 1 Uncultured bacterium clone 051011 T3S4 W T SDP 331 69 gi 482680808 gb KC836020 1 Uncultured bacterium clone C-101 70 gi 197359976 gb EU703237 1 Uncultured Actinomycetales bacterium clone XZNMC38 100 gi 223033479 gb FJ353204 1 Uncultured bacterium clone C7p3 ML 273 83 gi 223033973 gb FJ353698 1 Uncultured bacterium clone I9S18D ML 083 87 100gi 793958782 gb KP687038 1 Uncultured bacterium clone T6 0611 94 gi 260072812 gb GQ850555 1 Uncultured actinobacterium clone u101 100 gi 260072831 gb GQ850574 1 Uncultured actinobacterium clone d118 96 51 gi 197131256 gb EU930663 1 Uncultured actinobacterium clone PLF173 LSUCC0392 acSTL clade gi 312860470 gb HM856511 1 Uncultured Actinomycetales bacterium clone YL147 97 gi 317573447 gb HQ661252 1 Uncultured bacterium clone H-37 gi 1246764471 gb MG002170 1 Uncultured bacterium clone PS207 86 gi 193795783 gb EU852548 1 Uncultured actinobacterium clone SBC31 85 85 gi 4996392 dbj AB021332 1 Bacterium rJ14 75 gi 643403313 gb KF083030 1 Uncultured bacterium clone ncd985h01c1 54 88 gi 359327483 emb FQ660334 1 Uncultured bacterium 87 gi 24935355 gb AY145533 1 Actinomycetales bacterium GP-5 100 gi 24935356 gb AY145534 1 Actinobacterium GP-6 gi 294471361 gb GU591555 1 Uncultured bacterium clone M72 67 gi 217388856 gb FJ524959 1 Uncultured bacterium 051102 S1 W T SDP18 183 41 62 gi 388951535 gb JQ196204 1 Uncultured bacterium clone SeaWat O253 26 gi 61676995 gb AY948359 1 Uncultured bacterium clone sponge clone11 12 12gi 388954039 gb JQ198708 1 Uncultured bacterium clone SeaWat F743 27 2198gi 61676993 gb AY948357 1 Uncultured bacterium clone sponge clone8 1565 39 gi 1132313789 gb KX932758 1 Uncultured marine bacterium clone 70S3Bb05Y 29 gi 1132314281 gb KX933250 1 Uncultured marine bacterium clone 70SA1b05G 19 30 gi 224496639 gb FJ744948 1 Uncultured Actinomycetales bacterium clone SHWH night1 38 90 gi 672374989 gb KJ811951 1 Uncultured bacterium clone 0806N7 3 81 H06914 100 gi 1216866617 gb MF498123 1 Uncultured bacterium clone W1-60 gi 239775476 gb FJ999603 1 Uncultured Actinomycetales bacterium clone B61 72 gi 952074740 gb EU182063 2 Uncultured bacterium clone D15 7 SW G 42 63 gi 238481764 gb FJ937867 1 Uncultured actinobacterium clone MWLSB148 19 100 96 gi 239939247 gb GQ144861 1 Uncultured actinobacterium clone a-26 90 gi 891166350 dbj AB974135 1 Uncultured bacterium