Isolation and Characterization of Plasmid DNA in Streptococcus cremoris

Abstract

Nine industrially important strains of Streptococcus cremoris (HP, AM2, ML1, WC, C3, Ri, E8, KH, and Wg2) were shown to possess a diversity of plasmid molecules. Molecular weights of plasmids were determined from their relative mobilities after agarose gel electrophoresis and via electron microscopy. To illustrate the varied plasmid sizes, strain HP contained plasmids of 26, 18, 8.5, 3.3, and 2 megadaltons (Mdal); strain ML, contained plasmids of 29, 18, 9, 4, 2.2, and 1.8 Mdal; and strain AM2 had plasmids of 42, 27, 16, and 8.4 Mdal. The numbers of plasmids observed in the other strains were 6, 5, 5, 7, 5, and 4 for C3, E8, KH, R1, WC, and Wg2, respectively. A spontaneous proteinase-negative (Prt-) mutant of HP was missing the 8.5-Mdal plasmid, which suggests that in this strain prQteinase activity could be linked to this particular plasmid. A lactose-negative (Lac-) Prtmutant of ML, lacked the 2.2-Mdal plasmid. Under the conditions employed, antibiotic sensitivity and heavy-metal susceptibility did not correlate with the missing plasmid in Prt-HP or in the Lac-Prt-ML1. Curing experiments with AM2, using acridine dyes and elevated temperatures, did not yield Lacvariants. AM2 was also cultured at high dilution rates in a chemostat for 168 h by using a buffered milk or lactic broth at 18 or 32°C with no selection of Lacderivatives. The inability to obtain Lac-variants under conditions known to facilitate plasmid elimination suggests that lactose metabolism is not plasmidmediated in AM2.

Cloning and expression of a Streptococcus cremoris proteinase in Bacillus subtilis and Streptococcus lactis

“…According to this classification S. cremoris strains HP and Wg2 belong to the same group (11). Furthermore, it has been reported that S. cremoris HP carries a 9-Md proteinase plasmid (20). To investigate whether HindIII fragment C might specify proteinase activity, we examined its possible hybridization to the 9-Md proteinase plasmid of S. cremoris HP.…”

“…In many lactic acid streptococci proteolytic activity is an unstable trait. Plasmid curing studies suggested that this activity is specified by plasmids in some strains (19,20,25,26,29). However, only in a few cases has it been established that this proteolytic ability was actually plasmid encoded by showing the cotransfer of plasmid and character (12,15,25).…”

Conjugal Transfer of Lactose-Fermenting Ability Among Streptococcus cremoris and Streptococcus lactis Strains

“…Consecutive transfers in milk or broth containing fermentable carbohydrates other than galactose or lactose were observed to result in the appearance of organisms unable to ferment lactose. More recently, researchers demonstrated that the occurrence of lactosenegative (Lac-) mutants could be increased by consecutive transfers in broth containing acridine dyes (1,12,16,21), ethidium bromide (7,15,16), or by growing the culture at elevated temperatures which were restrictive to growth (1,7,15,16,21). Plasmid linkage of lactose metabolism was demonstrated in S. lactis and S. lactis subsp.…”

“…diacetylactis by the concomitant losses of plasmid deoxyribonucleic acid (DNA) and lactose-fermenting ability (7,12,15,21). Although similar studies were conducted with S. cremoris strains (16,21), only the atypical S. cremoris strain B1 was observed to simultaneously lose lactose metabolic capability and plasmid DNA (1). Studies directed toward confirming plasmid linkage to phenotypic properties have often employed genetic transfer systems (2,6,13,20,27,29).…”

Intergeneric transfer of the conjugative tetracycline-resistance transposon Tn916 from Streptococcus faecalis to Staphylococcus aureus

“…diacetylactis, and ^ cremoris) often harbor cryptic plasmids as well as plasmids responsible for lactose fermentation (Gasson, 1983;McKay et al, 1980;Walsh and McKay, 1982), casein degradation in milk (Larsen and McKay, 1978), citrate utilization by ^ lactis subsp. diacetylactis (Kempler and McKay, 1979), and diplococcin production (Dip+) by S.…”