90
et al. ( 1999 ) highlighted the inability of conventional systems to differentiate among
Renibacterium isolates, and investigated molecular methods that might be useful to
identify intraspecifi c variation. The outcome was the differentiation of isolates by
RAPD according to host and geographical location.
Box 3.2: Renibacterium salmoninarum
Characteristically, Ren. salmoninarum produces cream (non-pigmented),
shiny, smooth, round, raised, entire, 2-mm diameter colonies on KDM2 after
incubation at 15 °C for 20 days. Subclinical infections may lead to two colony
types, the smooth colonies described above and a thin fi lm of growth, the latter of which does not develop on SKDM (Hirvelä-Koski et al. 2006 ). Old
cultures, i.e. 12 weeks, may become extremely granular or crystalline in
appearance. Indeed, a transverse section through such colonies will reveal the
presence of a few Gram-positive rods embedded in a crystalline matrix.
Subculturing at this stage often leads to the development of more crystalline
‘colonies’. It is thought that the material is principally cystine, which has been
precipitated from the medium. For some strains, a uniformly turbid growth
occurs in broth, but for others, a sediment may develop. The cell wall peptidoglycan of renibacteria contains D-alanine, D-glutamic acid, glycine and
lysine as the diamino acids (Fiedler and Draxl 1986 ). The principal cell wall
sugar is glucose, but arabinose, mannose and rhamnose are also present
(Sanders and Fryer 1980 ). Here, there is a discrepancy with the more recent
work of Kusser and Fiedler ( 1983 ). These authors reported that the principal
cell wall sugar is galactose, with lesser amounts of N-acetyl-glucosamine,
rhamnose and N-acetyl-fucosamine. This is a curious anomaly insofar as the
same strain, i.e. the type strain (ATCC 33209), is common to both studies.
Mycolic acids are absent. Methyl-branched fatty acids form over 92 % of the
total fatty acid component of the cells, with 12-methyltetradecanoic (anteisoC 15 ), 13-methyldecanoic (iso-C 15 ) and 14-methylhexadecanoic (anteiso-C 17 )
as the major components. Straight chain fatty acids generally account for 1 %
of the total fatty acids, and unsaturated fatty acids are not detected at all. Over
81 % of the total fatty acids are composed of the lower melting point anteiso
acids, which may contribute to membrane fl uidity at low temperatures.
Unsaturated menaquinones with nine isoprene units are present. All strains
contain diphosphatidylglycerol, two major and six or seven minor glycolipids
and two unidentifi ed minor phospholipids (Embley et al. 1983 ). Although
renibacteria were considered to be serologically homogeneous (Bullock et al.
1974 ; Getchell et al. 1985 ), two antigenic groups have been described (Bandín
et al. 1992 ). These groups have been defi ned after analyses of membrane proteins, which determined the presence of 57 kDa and 30 kDa molecules in the
respective groups. The G + C ratio of the DNA has been calculated as 53.0
+/− 0.46 moles % by Sanders and Fryer ( 1980 ) and as 55.5 moles % by
Banner et al. ( 1991 ). Additional characteristics of Ren. salmoninarum have
been included in Table 3.1 .
(continued)
3 Aerobic Gram-Positive Rods and Cocci
et al. ( 1999 ) highlighted the inability of conventional systems to differentiate among
Renibacterium isolates, and investigated molecular methods that might be useful to
identify intraspecifi c variation. The outcome was the differentiation of isolates by
RAPD according to host and geographical location.
Box 3.2: Renibacterium salmoninarum
Characteristically, Ren. salmoninarum produces cream (non-pigmented),
shiny, smooth, round, raised, entire, 2-mm diameter colonies on KDM2 after
incubation at 15 °C for 20 days. Subclinical infections may lead to two colony
types, the smooth colonies described above and a thin fi lm of growth, the latter of which does not develop on SKDM (Hirvelä-Koski et al. 2006 ). Old
cultures, i.e. 12 weeks, may become extremely granular or crystalline in
appearance. Indeed, a transverse section through such colonies will reveal the
presence of a few Gram-positive rods embedded in a crystalline matrix.
Subculturing at this stage often leads to the development of more crystalline
‘colonies’. It is thought that the material is principally cystine, which has been
precipitated from the medium. For some strains, a uniformly turbid growth
occurs in broth, but for others, a sediment may develop. The cell wall peptidoglycan of renibacteria contains D-alanine, D-glutamic acid, glycine and
lysine as the diamino acids (Fiedler and Draxl 1986 ). The principal cell wall
sugar is glucose, but arabinose, mannose and rhamnose are also present
(Sanders and Fryer 1980 ). Here, there is a discrepancy with the more recent
work of Kusser and Fiedler ( 1983 ). These authors reported that the principal
cell wall sugar is galactose, with lesser amounts of N-acetyl-glucosamine,
rhamnose and N-acetyl-fucosamine. This is a curious anomaly insofar as the
same strain, i.e. the type strain (ATCC 33209), is common to both studies.
Mycolic acids are absent. Methyl-branched fatty acids form over 92 % of the
total fatty acid component of the cells, with 12-methyltetradecanoic (anteisoC 15 ), 13-methyldecanoic (iso-C 15 ) and 14-methylhexadecanoic (anteiso-C 17 )
as the major components. Straight chain fatty acids generally account for 1 %
of the total fatty acids, and unsaturated fatty acids are not detected at all. Over
81 % of the total fatty acids are composed of the lower melting point anteiso
acids, which may contribute to membrane fl uidity at low temperatures.
Unsaturated menaquinones with nine isoprene units are present. All strains
contain diphosphatidylglycerol, two major and six or seven minor glycolipids
and two unidentifi ed minor phospholipids (Embley et al. 1983 ). Although
renibacteria were considered to be serologically homogeneous (Bullock et al.
1974 ; Getchell et al. 1985 ), two antigenic groups have been described (Bandín
et al. 1992 ). These groups have been defi ned after analyses of membrane proteins, which determined the presence of 57 kDa and 30 kDa molecules in the
respective groups. The G + C ratio of the DNA has been calculated as 53.0
+/− 0.46 moles % by Sanders and Fryer ( 1980 ) and as 55.5 moles % by
Banner et al. ( 1991 ). Additional characteristics of Ren. salmoninarum have
been included in Table 3.1 .
(continued)
3 Aerobic Gram-Positive Rods and Cocci