def dbes2dbes_strands(dBEs):
    """
    add reverse strand editing methods in the dBEs dataframe
    
    :param dBEs: pandas dataframe with BE methods
    """
    from beditor.lib.global_vars import nt2complement
    dBEs_ = dBEs.copy()
    dBEs_['strand'] = '-'
    for col_nt in ['nucleotide', 'nucleotide mutation']:
        dBEs_[col_nt] = dBEs_[col_nt].apply(lambda x: nt2complement[x])
    dBEs = dBEs.append(dBEs_, sort=True)
    return dBEs
