AbiG, a genotypically novel abortive infection mechanism encoded by plasmid pCI750 of Lactococcus lactis subsp. cremoris UC653

Abstract

AbiG is an abortive infection (Abi) mechanism encoded by the conjugative plasmid pCI750 originally isolated from Lactococcus lactis subsp. cremoris UC653. Insensitivity conferred by this Abi manifested itself as complete resistance to 712 (936 phage species) with only partial resistance to c2 (c2 species). The mechanism did not inhibit phage DNA replication. The smallest subclone of pCI750 which expressed the Abi phenotype contained a 3.5-kb insert which encoded two potential open reading frames. abiGi (750 bp) and abiGii (1,194 bp) were separated by 2 bp and appeared to share a single promoter upstream of abiGi. These open reading frames showed no significant homology to sequences of either the DNA or protein databases; however, they did exhibit the typical low G؉C content (29 and 27%, respectively) characteristic of lactococcal abi genes. In fact, the G؉C content of a 7.0-kb fragment incorporating the abiG locus was 30%, which may suggest horizontal gene transfer from a species of low G؉C content. In this context, it is notable that remnants of IS elements were observed throughout this 7.0-kb region.

Detection and sequencing of the microcystin LR-degrading gene,mlrA, from new bacteria isolated from Japanese lakes

“…The identity was 35%, and positives were 50% on putative amino acids translated from positions 421–724 of the mlrA gene of MD‐1. The CAAX amino‐terminal protease originated from a part of the DNA in the plasmid pSOL1 sequence in Bacillus anthracis [21], and the CAAX protease family consists of various hypothetical protein sequences for which the function is unknown [22,23]. The sequence contains a highly conserved Glu‐Glu motif at the end of the alignment, plus two histidine residues that may be involved in zinc binding.…”

Control of Staphylococcus aureus Quorum Sensing by a Membrane-Embedded Peptidase

“…In S. aureus, there are at least four putative type II CAAX metalloproteases that are also annotated as members of the abortive infectivity (Abi) protein family. The Abi nomenclature for this class of metalloproteases was originally assigned based upon studies of phage resistance mechanisms in Lactococcus lactis (55). Despite the frequent use of this terminology, members of the Abi protein family are not believed to exert functions related to phage resistance (50).…”

Nucleotide sequence and analysis of the new chromosomal abortive infection geneabiNofLactococcus lactissubsp.cremorisS114

“…The DNA fragment of 817 bp containing ORF7 showed no significant homologies with any GenBank‐listed DNA sequences, particularly with abiA [2], abiB [3], abiC [4], abiD [5], abiD1 [6], abiEi , abiEii and abiF [7], abiG [8], abiH [9], abiI [10], abiJ or abi‐859 [11] and abiK [12]. Apparently a new unique lactococcal abi gene has been sequenced which was designated abiN .…”

“…Many natural lactococcal phage resistance mechanisms occur, classified as interference with phage adsorption, inhibition of phage DNA injection, DNA restriction modification, and abortive infection, as previously reviewed [1]. Several genes conferring abortive phage infection (Abi + ), usually associated with plasmid DNA elements, were cloned and sequenced [2–12]. Only one was shown to be located in the chromosome [9].…”