Em perl:
#!/usr/bin/perl
my (%hotu, %hpc)=();
while(<>){
my($pc,$otu,$v)=split;
$hpc{$pc}=1;
($hotu{$otu} or $hotu{$otu}={})->{$pc}+=$v;
}
#headers
my @apc = sort keys %hpc;
print join ("\t", 'OTU_ID', @apc) . "\n";
#values
foreach my $otu (sort keys %hotu) {
print join ("\t", $otu, map {$_=0 unless defined; $_} @{$hotu{$otu}}{@apc}) . "\n";
}