Genetic Complementation of the Obligate Marine Actinobacterium Salinispora tropica with the Large Mechanosensitive Channel GenemscLRescues Cells from Osmotic Downshock

Abstract

ABSTRACTMarine actinomycetes in the genusSalinisporafail to grow when seawater is replaced with deionized (DI) water in complex growth media. While bioinformatic analyses have led to the identification of a number of candidate marine adaptation genes, there is currently no experimental evidence to support the genetic basis for the osmotic requirements associated with this taxon. One hypothesis is that the lineage-specific loss ofmscLis responsible for the failure of strains to grow in media prepared with DI water. ThemscLgene encodes a conserved transmembrane protein that reduces turgor pressure under conditions of acute osmotic downshock. In the present study, themscLgene from aMicromonosporastrain capable of growth on media prepared with DI water was transformed intoS. tropicastrain CNB-440. The single-copy, chromosomal genetic complementation yielded a recombinantSalinispora mscL+strain that demonstrated an increased capacity to survive osmotic downshock. The enhanced survival of theS. tropicatransformant provides experimental evidence that the loss ofmscLis associated with the failure ofSalinisporaspp. to grow in low-osmotic-strength media.