Chromosome interactions and expression in fused Bacillus protoplasts

Heterodiploid bacteria can be regenerated from fused mixed protoplasts. In both B. megaterium and B. subtilis, early selective effects during regeneration may strongly affect the phenotype of the products. Among the products are diploid prototrophs, whose stability is still in doubt. It is not known whether the prototrophy results from complementation or from recombination during the selection. In the case of B. subtilis, regeneration in a permissive, uncrowded and non-selective environment leads to production of rather large yields of heterodiploids, either biparental or recombinant. These seem to be only partially stable, but while remaining diploid they give rise to a wide variety of genetic recombinants. In general rather few prototrophs are found when selection is applied to the bacterial diploids. The phenotypic properties of B. subtilis diploids reveal incomplete expression of the demonstrable gene inventory. Biparental diploids appear commonly to show the phenotype of only one of the contained parent types, as if one chromosome remains unexpressed. For diploid recombinants data are insufficient to reveal the status of the chromosomes. Non-expression is believed to be due to structural complexity of particular chromosomes, or their parts. Recombination occurring within bacterial heterodiploid clones appears to satisfy many of the expectations for genetic recombination in eukaryotes--including that of being in part at least classically reciprocal, with intraclonal reciprocals in equivalent numbers. While short map intervals show reduced recombination, large numbers of recombinations (one to two thirds) involve exchanges at or near the terminus and origin of bidirectional replication.(ABSTRACT TRUNCATED AT 250 WORDS)