Notes about COVID origins -


98.6% nucleotide identity in the partial RdRP fragment of RaTG13 is not unusual

In the 370-base partial RdRp sequence of 4991/RaTG13 which was published in 2016, there's 5 nucleotide changes and 1 amino acid change from Wuhan-Hu-1. So it has about 98.6% nucleotide identity with Wuhan-Hu-1 even though the whole genome of RaTG13 only has 96.1% identity, so people like Monali Rahalkar have been speculating that the rest of the genome of RaTG13 was fabricated to make it appear to be more distant to SARS2: []

WIV had deposited RdRp and ORF8 submission of 4991 in 2018 and so when they sequenced sars2 they should have found 4991 RdRp of almost 3000 bases with 98 percent and protein match should be 99 or more. What’s the guarantee that the rest was not that close too! Did they distance it

Was this the reason Shi lost her sleep that 4991 RdRp was 98 percent and on aa much more closer to sars2. So little tampering of this sequence into a synthetic or serial passage could result in a lab made sars2, and people would suspect them?

When the RaTG13 sequence came out on 27 Jan 2020, it was about 96.2 percent similar. Did they adjust it at other places so that the average came low? It’s like 98, 99 percent marks in many subjects and S protein 93 lowering the average marks to 96.2%?

However in the paper by Ge et al. from 2016 where the RdRp fragment was published, it was specifically called the "conserved 440-bp RdRp fragment": "Only two sequences detected in this study were homologous to betacoronaviruses. One of them (RaBtCoV/4991) was detected in a R. affinis sample and was related to SL-CoV. The conserved 440-bp RdRp fragment of RaBt-CoV/4991 had 89% nt identity and 95% aa identity with SL-CoV Rs672 (Yuan et al., 2010)." [] In the paper they also sequenced the same region from alphacoronaviruses, and it is one of the regions that is the most similar between alphacoronaviruses and betacoronaviruses.

The same region was also sequenced in the "discovery of a rich gene pool" paper by Hu et al. from 2016: "A total of 602 alimentary specimens (anal swabs or feces) were collected and tested for the presence of CoVs by a Pan-CoV RT-PCR targeting the 440-nt RdRp fragment that is conserved among all known α- and β-CoVs [20]." []

In the region of the RdRp fragment of RaTG13, for example Tor2 has only 3 nucleotide changes from WIV1 and SHC014, even though it has about 93-95% identity to them in the whole genome (but here the identity is a bit higher because I ignored positions where either sequence had a gap and I did a big multiple sequence alignment). Here the first column shows the number of nucleotide changes in the region of the partial RdRp sequence of 4991, and the second column shows the identity percentage in the whole genome:

$ curl -sL|gzip -dc>sarbe.fa;seqkit seq -g sarbe.fa>sarbe.ungap
$ wget
$ bow()([[ -e $1.1.bt2 ]]||bowtie2-build --threads 3 "$1" "$1";bowtie2 --no-unal -p3 -x "$@")
$ curl ''>4991.fa
$ bow sarbe.ungap -fU 4991.fa -a --score-min L,-1.5,-1.5|grep -v ^@|ruby -ane'puts [$F[2],$F[3],$F[3].to_i+$F[5].scan(/\d+(?=[MD])/).map(&:to_i).sum-1]*" "'|while read l m n;do seqkit grep -p $l sarbe.ungap|seqkit subseq -r $m:$n;done|seqkit grep -nrvp 'SARS coronavirus ZJ01'|mafft --quiet --thread 4 ->temp
$ x=Tor2;cat <(seqkit grep -nrp $x temp) temp|sed 's/\(,\| surface\).*//'|seqkit fx2tab|awk -F\\t 'NR==1{split($2,a,"");next}{split($2,b,"");d=0;for(i=1;i<=length;i++)if(a[i]!=b[i])d++;print d,$1}'|sort -n|awk 'NR==FNR{a[$2]=$1;next}{$1=$1"\t"a[$2]}1' <(awk -F\\t 'NR==1{for(i=2;i<=NF;i++)if($i~x)break;next}{print$i,$1}' x="$x" -|sed 's/ /\t/'|awk '$2==100||($2<98&&$0!~/SARS coronavirus/)'|head|column -ts$'\t'
0  100.0000  NC_004718.3 SARS coronavirus Tor2
1  93.5641   KP886808.1 Bat SARS-like coronavirus YNLF_31C
1  93.5506   KP886809.1 Bat SARS-like coronavirus YNLF_34C
2  92.0783   KU973692.1 UNVERIFIED: Severe acute respiratory syndrome-related coronavirus isolate F46
2  93.9236   KY417148.1 Bat SARS-like coronavirus isolate Rs4247
3  95.4596   KC881005.1 Bat SARS-like coronavirus RsSHC014
3  95.7228   KC881006.1 Bat SARS-like coronavirus Rs3367
3  95.6781   KF367457.1 Bat SARS-like coronavirus WIV1
3  95.8298   KY417144.1 Bat SARS-like coronavirus isolate Rs4084
3  93.8966   KY417149.1 Bat SARS-like coronavirus isolate Rs4255

RhGB05 and RhGB06 have only 1 nucleotide change in the region, but they have about 97% identity in the whole genome.

For example Anlong-112 also has 1-3 nucleotide changes in the same region with all the viruses in this simplot, even though the identity in the whole genome is around 90-96%:

Rahalkar also posted a screenshot of a SARS2 sample from 2024 at BLAST which had only 3 nucleotide changes from the 370-base RdRp fragment of 4991, and she wrote: "So now the virus is mutating back to the ancestor! Because the three base diff is a recent most sequence." [] However BLAST has millions of SARS2 samples, so just because one sample from 2024 has only 3 mutations doesn't mean it would be typical of all samples from 2024. NextStrain's global subset of SARS2 samples included 450 samples from 2024, but only one of the samples had 4 mutations in the 370-base region, 390 samples had 5 mutations, 56 had 6, and 3 had 7. So the average was higher than 5:

$ curl ''>4991.fa
$ curl|gzip -dc>global.fa
$ seqkit locate -f4991.fa -m8 <(seqkit head -n1 global.fa)|sed 1d|cut -f5,6|seqkit subseq -r $(tr \\t :) global.fa|seqkit grep -nrp '2024$'|seqkit grep -svp N|cat 4991.fa -|seqkit seq -s|awk 'NR==1{split($0,a,"");l=length;next}{split($0,b,"");d=0;for(i=1;i<=l;i++)if(a[i]!=b[i])d++;n[d]++}END{for(i in n)print i,n[i]}'
4 1
5 390
6 56
7 3

100% amino acid identity of the envelope protein of ZC45

Limeng Yan was making a big deal out of how the envelope protein of ZC45 had 100% amino acid identity to SARS2: []

The E protein is tolerant of mutations as evidenced in both SARS (Figure 2A) and related bat coronaviruses (Figure 2B). This tolerance to amino acid mutations of the E protein is further evidenced in the current SARS-CoV-2 pandemic. After only a short two-month spread of the virus since its outbreak in humans, the E proteins in SARS-CoV-2 have already undergone mutational changes. Sequence data obtained during the month of April reveals that mutations have occurred at four different locations in different strains (Figure 2C). Consistent with this finding, sequence blast analysis indicates that, with the exception of SARS-CoV-2, no known coronaviruses share 100% amino acid sequence identity on the E protein with ZC45/ZXC21 (suspicious coronaviruses published after the start of the current pandemic are excluded[18,27-31]), Although 100% identity on the E protein has been observed between SARS-CoV and certain SARS-related bat coronaviruses, none of those pairs simultaneously share over 83% identity on the Orf8 protein[32]. Therefore, the 94.2% identity on the Orf8 protein, 100% identity on the E protein, and the overall genomic/amino acid-level resemblance between SARS-CoV-2 and ZC45/ZXC21 are highly unusual. Such evidence, when considered together, is consistent with a hypothesis that the SARS-CoV-2 genome has an origin based on the use of ZC45/ZXC21 as a backbone and/or template for genetic gain-of-function modifications.

But if SARS1 has an identical envelope protein on the amino acid level with viruses where the ORF8 is less than 83% identical, then it suggests that there's nothing unusual if there's 100% aa identity for the envelope proteins of viruses that are not closely related.

The envelope protein of BtKY72 also has 100% amino acid identity to other African sarbecoviruses even though they only have about 85% nucleotide identity in the whole genome:

$ curl -sL|gzip -dc>sarbe.fa;wget
$ emu()(curl -sd "id=$(paste -sd,)" "${1:-nuccore}&rettype=${2:-fasta}&retmode=$3")
$ seqkit seq -ni sarbe.fa|emu '' fasta_cds_aa|seqkit grep -nrp 'gene=E\b|envelope|protein=E\b'>env.aa
$ sed 's/lcl|//;s/_prot.*//' env.aa|seqkit fx2tab|awk -F\\t 'NR==FNR{a[$1]=$2;next}{print">"$1" "a[$1]"\n"$2}' <(seqkit seq -n sarbe.fa|sed $'s/ /\t/;s/\(,\| surface\| ORF1\).*//') ->env2.aa
$ masog()(awk -F\\t 'NR==1{for(i=2;i<=NF;i++)if($i~x)break;next}{print$i,$1}' x="$1" "${2--}"|sort -n)
$ pid0()(seqkit fx2tab "$@"|awk -F\\t 'NR==1{split($2,a,"");l=length;next}{split($2,b,"");d=0;n=0;for(i=1;i<=l;i++){n++;if(a[i]!=b[i])d++}print 100*(1-d/n),$1}')
$ x=BtKY72;seqkit grep -nrp $x env2.aa|cat - env2.aa|pid0|sort -rn|awk 'NR==FNR{a[$2]=$1;next}{$1=$1" "a[$2]}1' <(masog $x -|head
100 85.3537 MT726045.1 Sarbecovirus sp. isolate PREDICT/PRD-0038/AABSMF
100 85.4618 MT726044.1 Bat coronavirus isolate PREDICT/PDF-2370/OTBA35RSV
100 85.4618 MT726043.1 Sarbecovirus sp. isolate PREDICT/PDF-2386/OTBA40RSV
100 100.0000 KY352407.1 Severe acute respiratory syndrome-related coronavirus strain BtKY72
99.359 81.7080 MZ190137.1 Bat SARS-like coronavirus Khosta-1 strain BtCoV/Khosta-1/Rh/Russia/2020
97.4359 78.1437 OR233314.1 Horseshoe bat sarbecovirus isolate Rt22SL92
97.4359 78.1471 OR233313.1 Horseshoe bat sarbecovirus isolate Rt22SL85
97.4359 78.1471 OR233312.1 Horseshoe bat sarbecovirus isolate Rt22SL58
97.4359 78.1437 OR233311.1 Horseshoe bat sarbecovirus isolate Rt22SL130
97.4359 78.0657 OR233303.1 Horseshoe bat sarbecovirus isolate Rt22SL9

Tor2 and HKU3 also have an identical envelope protein on the amino acid level even though they only have about 88% nucleotide identity in the whole genome (in a multiple sequence alignment where positions where either sequence has a gap are ignored):

$ x=Tor2;seqkit grep -nrp $x env2.aa|cat - env2.aa|pid0|sort -rn|awk 'NR==FNR{a[$2]=$1;next}{$1=$1" "a[$2]}1' <(masog $x -|awk '$1==100'|sort -nk2|head
100 82.2274 OR233309.1 Horseshoe bat sarbecovirus isolate Rt22SL67
100 88.0533 DQ084199.1 bat SARS coronavirus HKU3-2
100 88.0562 DQ084200.1 bat SARS coronavirus HKU3-3
100 88.0597 DQ022305.2 Bat SARS coronavirus HKU3-1
100 88.1371 OK017837.1 Sarbecovirus sp. isolate JX2021C
100 88.2051 OK017801.1 Sarbecovirus sp. isolate HB2020D
100 88.2333 OK017845.1 Sarbecovirus sp. isolate JX2021P
100 88.2441 OK017808.1 Sarbecovirus sp. isolate FJ2021A
100 88.3719 OK017844.1 Sarbecovirus sp. isolate JX2021O
100 88.3878 OQ503499.1 Severe acute respiratory syndrome-related coronavirus isolate RsHB190371

The novel HKU3-like virus mentioned in DRASTIC's HZAU paper was published in 2023 as RsGD2014A/RsGD2014B

The paper by DRASTIC titled "Unexpected novel Merbecovirus discoveries in agricultural sequencing datasets from Wuhan, China" said: []

A significant amount of reads of a SARS-r CoV most closely related to HKU3 was identified in a Mus Musculus splenocyte RNA-seq sequencing dataset SRR5819071 in BioProject PRJNA393936. The novel bat SARS-like HKU3-related CoV was identified via BLAST analysis of the dataset, with the reads only 96-98% similar to their closest related GenBank sequences (Supp. Fig. 27, Supp. Table 4). Although the sequences are far too few to be assembled, the presence of transcription regulatory sequence (TRS)-leader associated fusion reads between the TRS-leader and the TRS-N gene suggest active replication of the HKU3-r CoV within the Mus Musculus splenocyte sample.

Even though most of the other runs discussed in the paper were submitted by Huazhong Agricultural University or Fujian Agriculture and Forestry University, the SRR5819071 run which contained the HKU3-like virus was submitted by WIV.

When I aligned the reads in the run against sarbecovirus sequences, I got the highest number of covered bases for the isolates 141376 and 141341 which were published in 2023, and the average error rates for them were only about 0.40% and 0.08%:

$ curl -sL|gzip -dc>sarbe.fa
$ seqkit seq -g sarbe.fa|seqkit fx2tab|sed $'s/A*\t$//'|seqkit tab2fx| window=20 in=stdin out=sarbe.mask
$ bowtie2-build --threads 3 sarbe.fa{,}
$ x=SRR5819071;bowtie2 -p 3 --no-unal -x sarbe.mask -1 ${x}_1.fastq.gz -2 ${x}_2.fastq.gz --score-min L,-1,-1|samtools sort -@3 ->$x.sarbe.bam
$ covera()(samtools coverage "$1"|awk \$4|cut -f1,3-6|(gsed -u '1s/$/\terr%\tname/;q';sort -rnk5|awk -F\\t -v OFS=\\t 'NR==FNR{a[$1]=$2;next}{print$0,sprintf("%.2f",a[$1])}' <(samtools view $x|awk -F\\t '{x=$3;n[x]++;len[x]+=length($10);sub(/.*NM:i:/,"");mis[x]+=$1}END{for(i in n)print i"\t"100*mis[i]/len[i]}') -|awk -F\\t 'NR==FNR{a[$1]=$2;next}{print$0"\t"a[$1]}' <(seqkit seq -n "${2-~/viral.fa}"|gsed 's/ /\t/;s/,.*//') -)|column -ts$'\t')
$ covera $x.sarbe.bam sarbe.mask
#rname     endpos numreads covbases coverage err%  name
OQ503496.1 29646  10       1355     4.5706   0.40  Severe acute respiratory syndrome-related coronavirus isolate 141376
OQ503495.1 29657  8        837      2.82227  0.08  Severe acute respiratory syndrome-related coronavirus isolate 141341
OQ297705.1 30029  846586   350      1.16554  6.01  MAG: Severe acute respiratory syndrome-related coronavirus isolate CQ/L80.18/2021
OP776339.1 30600  3        234      0.764706 15.93 Sarbecovirus sp. isolate RhGB05
OQ297732.1 29568  2        200      0.676407 1.33  MAG: Severe acute respiratory syndrome-related coronavirus isolate GD/L105.18/2022
OK017815.1 29550  2        193      0.65313  0.33  Sarbecovirus sp. isolate GD2017I
KF294457.1 29676  2        182      0.61329  0.00  Bat SARS-like coronavirus isolate Longquan-140 orf1ab polyprotein
OL674076.1 29780  116980   159      0.533915 20.76 Severe acute respiratory syndrome-related coronavirus isolate Rs7907
OK017841.1 29350  1        150      0.511073 0.67  Sarbecovirus sp. isolate JX2021L
OQ503500.1 30385  146      151      0.496956 21.70 Severe acute respiratory syndrome-related coronavirus isolate 4105
OQ503498.1 30172  2        137      0.454063 16.33 Severe acute respiratory syndrome-related coronavirus isolate BDA190366
KY417144.1 29770  2        132      0.443399 0.00  Bat SARS-like coronavirus isolate Rs4084
OK017842.1 29337  2        120      0.40904  0.00  Sarbecovirus sp. isolate JX2021M
OQ503504.1 30325  11539    118      0.389118 22.24 Severe acute respiratory syndrome-related coronavirus isolate 162173

When I ran MEGAHIT on the reads which aligned against sarbecoviruses, my longest contig was 535 bases long and it was 100% identical to both 141376 and 141341:

x=SRR5819071;samtools view $x.sarbe.bam|grep -Ev 'OQ297705|OL674076|OQ503504'|cut -f1,10|seqkit tab2fx>temp.fa
megahit -r temp.fa --min-count 1 -o megatemp;seqkit sort -lr megatemp/final.contigs.fa

The 141376 and 141341 isolates actually have over 5% nucleotide distance from HKU3:

The 141376 and 141341 isolates were published in a paper by WIV titled "Isolation of ACE2-dependent and -independent sarbecoviruses from Chinese horseshoe bats", where the corresponding authors were Zhengli Shi and Michael Letko. [] In the paper the isolates were given the identifiers RsGD2014A and RsGD2014B. Supplementary Table 1 says that RsGD2014A and RsGD2014B are identical (even though at GenBank 141376 has two nucleotide changes from 141341, but I guess they're still virtually identical):

RsGD2014A seems to have some S1 recombination action going on, which is totally unexpected from a virus published by the WIV. The NTD is virtually identical to GD2017H and RaCH025:

If RsGD2014A is compared to GD2017H, there are also breakpoints in the slope of cumulative synonymous mutations near the start and end of the RBD:

The HA segment in WIV07-2 matches the 2013 refseq but other segments match newer strains of H7N9

In 2021 Steven Quay et al. published a preprint which showed that in the raw reads of samples from early COVID patients published by WIV, there were also reads which contained the HA segment of influenza A within a pVAC1 expression vector: Influenza viruses are segmented viruses which contain a total of 8 segments, similar to how the human genome is divided into chromosomes. Segment 4 codes for the hemagglutin protein, which is the equivalent of the spike protein in coronaviruses.

The WIV reads also contained a much smaller number of reads for other segments of H7N9, even though Quay wrote: "Mr. Cullen fails to state that the H7N9 sequences found in the patients were one gene only, attached to a laboratory vector." [] However later he corrected himself and wrote: "Correction: 5 of 6 did not have all of the influenza genes. 1 of 6 had all of the genes but non-HA genes at <2% of HA. HA is in a synthetic vector as in a vaccine." []

The run with the highest number of H7N9 reads has the ID WIV07-2. It has about 17,000 reads that match segment 4 but only about 150 reads which match other segments of H7N9.

The H7N9 reference sequence comes from a sample collected from a human patient in China in 2013, even though H7N9 samples from humans are otherwise fairly rare. When I aligned the reads of WIV07-2 against the refseq, I got an error rate of about 0.3% for reads that aligned against segment 4 (HA) and 0.3% for segment 8, but I got an error rate of 1.6-3.5% for the other segments (and there were only 4 reads which aligned against segment 8 so the low error rate may have been due to chance). So I thought that maybe the other segments come from a different source than segment 4:

brew install seqkit bowtie2 samtools gnu-sed

curl ""|sed 1d|cut -f1|tr \; \\n|sed s,^,ftp://,|xargs wget

esearch -db nuccore -query '(h7n9[organism] OR wuhan-hu-1) AND refseq[filter]'|efetch -format fasta|seqkit replace -isp 'a{5,}$'>h7n9sars2.fa

bowtie2-build h7n9sars2.fa{,}
bowtie2 -p4 --no-unal --local -x h7n9sars2.fa -1 SRR11092059_1.fastq.gz -2 SRR11092059_2.fastq.gz|samtools sort -@3 ->SRR11092059.local.bam

x=SRR11092059.local.bam;samtools coverage $x|awk \$4|cut -f1,3-6|(gsed -u '1s/$/\terr%\tname/;q';sort -rnk3|awk -F\\t -v OFS=\\t 'NR==FNR{a[$1]=$2;next}{print$0,sprintf("%.2f",a[$1])}' <(samtools view $x|awk -F\\t '{x=$3;n[x]++;len[x]+=length($10);sub(/.*NM:i:/,"");mis[x]+=$1}END{for(i in n)print i"\t"100*mis[i]/len[i]}') -|awk -F\\t 'NR==FNR{a[$1]=$2;next}{print$0"\t"a[$1]}' <(seqkit seq -n h7n9sars2.fa|gsed 's/ /\t/;s/,.*//') -)|column -ts$'\t'
#rname       endpos  numreads  covbases  coverage  err%  name
NC_026425.1  1708    17346     1685      98.6534   0.31  Influenza A virus (A/Shanghai/02/2013(H7N9)) segment 4 hemagglutinin (HA) gene
NC_045512.2  29870   5214      29843     99.9096   0.22  Severe acute respiratory syndrome coronavirus 2 isolate Wuhan-Hu-1
NC_026422.1  2280    107       2201      96.5351   3.29  Influenza A virus (A/Shanghai/02/2013(H7N9)) segment 1 polymerase PB2 (PB2) gene
NC_026427.1  980     27        543       55.4082   2.57  Influenza A virus (A/Shanghai/02/2013(H7N9)) segment 7 matrix protein 2 (M2) and matrix protein 1 (M1) genes
NC_026423.1  2297    10        671       29.212    3.47  Influenza A virus (A/Shanghai/02/2013(H7N9)) segment 2 polymerase PB1 (PB1) and PB1-F2 protein (PB1-F2) genes
NC_026428.1  841     4         140       16.6468   0.33  Influenza A virus (A/Shanghai/02/2013(H7N9)) segment 8 nuclear export protein (NEP) and nonstructural protein 1 (NS1) genes
NC_026426.1  1499    4         349       23.2822   2.00  Influenza A virus (A/Shanghai/02/2013(H7N9)) segment 5 nucleocapsid protein (NP) gene
NC_026424.1  2176    2         207       9.51287   1.67  Influenza A virus (A/Shanghai/02/2013(H7N9)) segment 3 polymerase PA (PA) and PA-X protein (PA-X) genes

Next I tried aligning the WIV07-2 reads against all H7N9 sequences from the NCBI's influenza virus database: The 5 samples with the highest number of aligned reads for segment 4 were all from the year 2013. Out of a total of 750 sequences for segment 4 in my FASTA file, I got the highest number of aligned reads for A/Shanghai/02/2013, which is the H7N9 refseq:

#rname    endpos  numreads  covbases  coverage  err%   name
KF021597  1708    621       1685      98.6534   0.34   A/Shanghai/02/2013;4;China;2013;03;05;Human
CY146908  1683    603       1674      99.4652   0.32   A/chicken/Guangdong/SD641/2013;4;China;2013;05;03;Avian
KJ395948  1683    600       1594      94.7118   0.26   A/chicken/Guangdong/G2/2013;4;China;2013;05;05;Avian
KP413700  1683    578       879       52.2282   0.26   A/chicken/Dongguan/4195/2013;4;China;2013;12;19;Avian
KM879322  1683    325       1505      89.4236   0.28   A/chicken/Zhejiang/DTID-ZJU06/2013;4;China;2013;12;;Avian

However segment 1 got most aligned reads against samples from 2017 (top 5 samples shown):

#rname    endpos  numreads  covbases  coverage  err%   name
MG575543  2280    50        1866      81.8421   1.69   A/chicken/Anhui/AH395/2017;1;China;2017;03;06;Avian
KY621539  2341    8         279       11.918    1.08   A/Qingyuan/GIRD01/2017;1;China;2017;01;14;Human
MF630106  2280    6         254       11.1404   1.00   A/chicken/Guangdong/SD027/2017;1;China;2017;01;18;Avian
KY643838  2340    6         484       20.6838   1.33   A/Guangdong/SP440/2017;1;China;2017;01;04;Human
MF630458  2280    4         248       10.8772   3.67   A/duck/Hunan/S40506/2015;1;China;2015;11;16;Avian

Segment 7 also seems to match newer samples from around the year 2017:

#rname    endpos  numreads  covbases  coverage  err%  name
MW100646  1027    4         247       24.0506   1.50  A/chicken/Hunan/5.24_YYGK49P2-OC/2017;7;China;2017;05;24;Avian
MZ803120  1000    2         227       22.7      0.00  A/mallard/South Korea/20X-20/2021;7;South Korea;2021;01;06;Avian
MW265394  982     2         160       16.2933   1.00  A/chicken/Shanxi/SX0256/2019;7;China;2019;01;10;Avian
MW109507  1027    2         125       12.1714   0.67  A/environment/Jiangxi/2.06_SRGFYF005-E/2017;7;China;2017;02;06;Environment
MW109475  982     2         226       23.0143   1.00  A/environment/Jiangxi/1.11_NCDZT98F2-E/2017;7;China;2017;01;11;Environment

So it could be that the HA plasmid was designed based on the refseq strain from 2013, but the full virus came from a newer strain of H7N9.

Is SARS2 phylogenetically closer to RaTG13 or BANAL-20-52?

Steve Massey has been saying that SARS 2 is phylogenetically closer to RaTG13 than to BANAL-52 because it groups together with RaTG13 in maximum likelihood trees: []

However the same thing can even happen in a distance-based tree. The tree below is based on a percentage distance of the whole genome so that positions where either sequence has a gap are not considered. I used the complete linkage method where the distance between two branches is the distance between the furthest nodes within the branches, so that for example the distance between SARS2 and the branch that contains the three BANAL viruses is the distance between SARS2 and the BANAL virus which is the furthest from SARS2, which happens to be BANAL-236. In my tree first BANAL-103 is joined with BANAL-236, and then their combined branch is joined with BANAL-52. And after that Wuhan-Hu-1 ends up being closer to RaTG13 than to the branch of the three BANAL viruses, so Wuhan-Hu-1 joins RaTG13 earlier:

The branching pattern remained the same even when I changed the linkage method from complete to ward.D2. But when I removed BANAL-236 and BANAL-103 from the tree, then Wuhan-Hu-1 joined with BANAL-52 before RaTG13:

brew install iqtree mafft seqkit xz
wget{pid,fa.xz};xz -d sarbe.fa.xz

# thin out a TSV percentage identity matrix to remove sequences with over n% identity to any previous sequence (default 99%)
thin()(awk -F\\t 'NR>1{for(i=2;i<NR;i++)if($i>x)next;print$1}' x="${1-99}" "${@:2}")

# matrix sort grep (sort TSV matrix by column that matches regex and print the column along with the first column)
masog()(awk -F\\t 'NR==1{for(i=2;i<=NF;i++)if($i~x)break;next}{print$i,$1}' x="$1" "${2--}"|sort -n)

# short name
shorn()(sed -E $'s/(,| surface| ORF1| orf1| genomic sequence).*//;s/Severe acute respiratory syndrome/SARS/;s/ isolate / /')
shorn2()(shorn|sed 's/ RNA$//;s/>.* />/')

# select sequences with at least 92% identity to Wuhan-Hu-1; omit sequences with over 99.9% identity to another sequence
masog Hu-1<|awk '$1>=90{print$2}'|sort|comm -12 <(thin 99.9|cut -d\  -f1|sort) -|seqkit grep -f- sarbe.fa|shorn2|mafft --thread 4 --quiet ->iqtree.fa
seqkit grep -nvrp '20-(103|236)' iqtree.fa>iqtree2.fa

curl -Ls>pid.cpp;g++ pid.cpp -O3 -o pid

hc=hclust(as.dist(m)) # complete linkage
# hc=hclust(as.dist(t),"ward.D2") # Ward linkage


In a world where more RaTG13-like viruses would be published, RaTG13 might join other RaTG13-like viruses earlier than SARS2. So then if the other RaTG13-like viruses would be further from SARS2 than RaTG13 is, it would increase the distance between SARS2 and the branch of RaTG13-like viruses, so then SARS2 might join the BANAL branch before the branch of RaTG13-like viruses. So therefore which branch is joined by SARS2 first might depend on which branch has more published sequences.

In the output below I used IQTree to generate maximum likelihood trees. On the left side where I included all 5 BANAL viruses, Wuhan-Hu-1 is grouped together with RaTG13. But on the right side where I again removed BANAL-103 and BANAL-236, Wuhan-Hu-1 is grouped together with BANAL-52 and not RaTG13. So a similar phenomenon I demonstrated above using a distance-based tree can also occur in a maximum likelihood tree:

$ iqtree -nt AUTO -s iqtree.fa;iqtree -nt AUTO -s iqtree2.fa
$ paste <(echo $'--- All five BANAL viruses included ---\n';sed '1,/^NOTE:/d' iqtree.fa.iqtree|sed 1d|sed '/^$/q') <(echo $'--- BANAL-103 and BANAL-236 excluded ---\n';sed '1,/^NOTE:/d' iqtree2.fa.iqtree|sed 1d|sed '/^$/q')|column -ts$'\t'
--- All five BANAL viruses included ---                                   --- BANAL-103 and BANAL-236 excluded ---
+**Ra22QT137                                                              +**Ra22QT137
|                                                                         |
+**Ra22QT106                                                              +**Ra22QT106
|                                                                         |
|  +--Ra22QT135                                                           |  +--Ra22QT135
+**|                                                                      +**|
   |  +--Ra22QT77                                                            |  +--Ra22QT77
   +--|                                                                      +--|
      |                           +--Wuhan-Hu-1                                 |                       +--Wuhan-Hu-1
      |                        +--|                                             |                    +--|
      |                        |  +-----RaTG13                                  |                    |  +--BANAL-20-52_Laos_2020
      |                     +--|                                                |                 +--|
      |                     |  +--BANAL-20-52_Laos_2020                         |                 |  +-----RaTG13
      |                  +--|                                                   |              +--|
      |                  |  |  +--BANAL-20-236_Laos_2020                        |              |  |      +--bat_Yunnan_RpYN06_2020
      |                  |  +--|                                                |              |  |  +---|
      |                  |     +--BANAL-20-103_Laos_2020                        |              |  |  |   |               +--PrC31
      |               +--|                                                      |              |  |  |   +---------------|
      |               |  |      +--bat_Yunnan_RpYN06_2020                       |              |  |  |                   |   +--YN2021
      |               |  |  +---|                                               |              |  |  |                   +---|
      |               |  |  |   |              +--PrC31                         |              |  |  |                       |        +--Rp22DB159
      |               |  |  |   +--------------|                                |              |  |  |                       +--------|
      |               |  |  |                  |   +--YN2021                    |              |  |  |                                +--BtSY2
      |               |  |  |                  +---|                            |              |  +--|
      |               |  |  |                      |        +--Rp22DB159        |              |     |        +--BANAL-20-247_Laos_2020
      |               |  |  |                      +--------|                   |              |     |    +---|
      |               |  |  |                               +--BtSY2            |              |     |    |   +--BANAL-20-116_Laos_2020
      |               |  +--|                                                   |              |     +----|
      |               |     |       +--BANAL-20-247_Laos_2020                   |              |          |            +--RacCS271
      |               |     |    +--|                                           |              |          +------------|
      |               |     |    |  +--BANAL-20-116_Laos_2020                   |              |                       |  +--RacCS253
      |               |     +----|                                              |              |                       +--|
      |               |          |            +--RacCS271                       |              |                          +--RacCS203
      |               |          +------------|                                 +--------------|
      |               |                       |  +--RacCS253                                   |                         +--GD_P79-9_2019
      |               |                       +--|                                             +-------------------------|
      |               |                          +--RacCS203                                                             +--MP789
                      |                       +--GD_P79-9_2019