The basic characteristics of the larger isolated 
elements, especially the giant DNA elements, are 
not unlike those of representative plasmids iso¬ 
lated from members of other genera of bacteria 
(Clowes, 1972). However, assignment of specific 
genetic functions to any of the B. thuringiensis or 
B. popilliae DNA elements is speculative at this 
time. There is some evidence, however, indicating 
that plasmid(s) may be involved in the synthesis of 
the parasporal crystals {B.t. 6-endotoxin) that are 
responsible for the pathogenicity of S. thuringien¬ 
sis to pest insects (Debavov et at., 1977; Stahly et 
al., 1978), 
Most of the described plasmids in bacilli (Lovett 
and Bramucci, 1 975; Lovett et at., 1976 ; Tanaka et 
al., 1977 ) are crytic elements lacking genetic 
markers and are unsuitable for selection of trans¬ 
formed colonies. Bernhard et al. ( 1978 ), however, 
have undertaken a search for plasmids in Bacillus 
species, mainly Bacillus cereus and B. subtilis, to 
characterize their properties and develop their 
potential use as vectors for gene cloning. Most of 
the S. cereus strains contained two or more plas¬ 
mids with molecular weights ranging from 1 . 6 'X 
1 0® to 1 05 X 1 06. Bacteriocin production could be 
attributed to a 45 x IQS-dalton plasmid from B. 
cereus, and tetracycline resistance to a 2.8 x 10^ 
plasmid from B. cereus. The plasmid carrying res¬ 
istance to tetracycline which was originally iso¬ 
lated from B. cereus, could be subsequently 
transformed in B.subtilis, where it was stably main¬ 
tained. Varietal types of 6. thuringiensis have been 
shown to be resistant to streptomycin (Afrikian, 
1960), penicillin, polymyxin B, nystatin. Bacitracin, 
viomycin (Ignoffo, 1963; Krieg, 1969), oxytetracy- 
cline (Fargette and Grelet, 1976), and tetracycline 
(Fargette et al., 1978; Rapport et al., 1978). Bacte¬ 
riocin production has also been identified in B. thu- 
ringienses (Krieg, 1970). Obviously, further 
genetic and biochemical studies are necessary 
for the determination of the biological functions of 
extrachromosomal DNA elements in 8. thurin¬ 
giensis and 8, popilliae and to definitely determine 
which isolated elements are indeed autonomous 
replicons. 
Asporogenic mutants of 8. thuringiensis are 
available (Nishiitsutsuji-Uwo and Yoshiharu, 
1975; Yousten, 1978) to preclude the supposed 
problem of persistence through sporulation. How¬ 
ever, if the researcher is not combining potentially 
hazardous DNA or hazardous heterlogous 
markers, or in cases where 8. thuringiensis, B. 
popilliae, or other safe entomopathogenic spe¬ 
cies, is being amplified in the same or other ento¬ 
mopathogenic species shown safe, I do not see 
the necessity of restriction to asporogenous 
strains. 
A number of bacteriophages have been 
reported in entomopathogenic bacteria and some 
have been suggested for use in mediating gener¬ 
alized transduction in 8. thuringlensis{Thome, 
1978; Van Tassell and Yousten, 1976; Acker- 
mannn et al., 1974; Chapman and Norris, 1966; 
Colasito and Rogoff, 1 969; De Barjac et al. 1974; 
Norris, 1961; Yoder and Nelson 1960). In fact 
some examples of cotransduction of linked 
markers in 8, thuringiensis have been presented, 
demonstrating the feasibility of chromosomal 
mapping in this organism (Thorne, 1978). Two lin¬ 
kage groups were demonstrated. One group 
included linkage of trp-1 to cys-1 and cys-2 but 
not to met-1. The second group included linkage 
of met-1 to arg-1 and arg-2 but not to arg-3. The 
cys-1 and cys-2 mutants were able to grow on 
cysteine, methionine, homocysteine, or cystathio¬ 
nine, but not on sulfide. Mutations conferring this 
phenotype are not represented on the current 8. 
subtilis chromosomal map (Young and Wilson, 
1975), The met-1 mutant has a strict requirement 
for methionine and may be analogous to metC or 
metD of 8, subtilis. The arg-1 and arg-2 mutants 
were able to grow on arginine, ornithine, or citrul- 
line and may be analogous to argO mutants of 8. 
subtilis, whereas the arg-3 mutant which grew 
only on arginine may be analogous to argA. 
Another bacteriophage (CP-51) grown in eight 
varieties of 8. thuringiensis has similar character¬ 
istics to those of the phage grown in 8 . cereus. 
Since this phage successfully transduced several 
auxotrophic markers in 6 . cereus. it appears pos¬ 
sible that it will also be able to mediate gene 
transfer in 8. thuringiensis (Van Tassell and 
Yousten, 1976). Transduction studies involving 
transducing phages and auxotrophic mutants 
would probably contribute significantly to an 
understanding of the molecular biology of 8. thu¬ 
ringiensis and to subsequent genetic engineering 
for producing more virulent strains. 
There are some disadvantages of the entomo¬ 
pathogenic bacteria for use as host systems. 
Chromosomal mapping and the knowledge of 
genetics and physiology of plasmids and bacterio¬ 
phages is ill-defined in these bacteria. High fre¬ 
quency, specialized transformation and 
transduction is not well known as a means of gene 
enrichment. To my knowledge the only work des¬ 
cribed on transformation in 6 . thuringiensis is that 
of Reeves (1966). Transformation of DNA mediat¬ 
ing the production of /3-exotoxin and 6-endotoxin 
from 8. thuringiensis var thuringiensis to 8 . thurin¬ 
giensis var finitimus was described. 8. thuringien¬ 
sis var finitimus does not produce /3-exotoxin, and 
the parasporal crystals produced by this variety 
are not toxic to most Lepidopteran larvae, espe¬ 
cially the cabbage looper and salt marsh caterpil¬ 
lar. Transformed isolates of 8. thuringiensis var 
6 
