Opening and editing multiple files in a folder with python

I am trying to modify my .fasta files from this:

>YP_009208724.1 hypothetical protein ADP65_00072 [Achromobacter phage phiAxp-3]
MSNVLLKQ...

>YP_009220341.1 terminase large subunit [Achromobacter phage phiAxp-1]
MRTPSKSE...

>YP_009226430.1 DNA packaging protein [Achromobacter phage phiAxp-2]
MMNSDAVI...

to this:

>Achromobacter phage phiAxp-3
MSNVLLKQ...

>Achromobacter phage phiAxp-1
MRTPSKSE...

>Achromobacter phage phiAxp-2
MMNSDAVI...

Now, I've already have a script that can do it to a single file:

with open('Achromobacter.fasta', 'r') as fasta_file:
    out_file = open('./fastas3/Achromobacter.fasta', 'w')
    for line in fasta_file:
        line = line.rstrip()
        if '[' in line:
            line = line.split('[')[-1]
            out_file.write('>' + line[:-1] + "\n")
        else:
            out_file.write(str(line) + "\n")

but I can't get to automate the process for all 120 files in my folder.

I tried using glob.glob, but I can't seem to make it work:

import glob

for fasta_file in glob.glob('*.fasta'):
    outfile = open('./fastas3/'+fasta_file, 'w')
    with open(fasta_file, 'r'):
        for line in fasta_file:
            line = line.rstrip()
            if '[' in line:
                line2 = line.split('[')[-1]
                outfile.write('>' + line2[:-1] + "\n")
            else:
                outfile.write(str(line) + "\n")

it gives me this output:

A
c
i
n
e
t
o
b
a
c
t
e
r
.
f
a
s
t
a

I managed to get a list of all files in the folder, but can't open certain files using the object on the list.

import os


file_list = []
for file in os.listdir("./fastas2/"):
    if file.endswith(".fasta"):
        file_list.append(file)