my @array = <FILE>; stores the lines of your file in the array. They still need to be split into columns:

use strict;
use warnings;
use Data::Dumper;
my @array = <DATA>;  # now contains the rows 
print Dumper(\@array);
$array[$_] = [ split /\s+/, $array[$_] ] for 0..$#array; # split lines
+ into columns
print Dumper(\@array);
print $array[0][0];

# does not look like CSV...
__DATA__
organism    O2_REQUIREMENT    Domain    Classification
a.acidocaldarius    Aerobe    BACTERIA    FIRMICUTES
a.actinomycetemcomitans    Facultative    BACTERIA    PROTEO
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