The second messenger cyclic di-AMP (c-di-AMP) is a stress-signal in most Gram-positive bacteria that plays a regulator of osmotic resistance through its control of potassium and compatible solute transport. Our previous work in a model strain of Lactococcus lactis has revealed high c-di-AMP mutants can restore their salt resistance by acquiring mutations that simply lower the c-di-AMP level or by elevating potassium uptake. To identify more mechanisms whereby cells can alter their osmoresistance independently of c-di-AMP level changes, we carried out a salt resistance suppressor screen using a phenotypically different strain of L. lactis. Using a spontaneous mutant of this strain (gdpP) which has high c-di-AMP, we obtained 25 suppressor mutants that had restored salt resistance and identified 5 independent mutations in the jag gene. Jag is a putative RNA-binding protein that has been reported to be involved in cell elongation and cell size via its direct interaction with the peptidoglycan lytic transglycosylase MltG. The Jag-MltG interaction in Lactococcus was confirmed using a bacterial two-hybrid assay. We found jag mutant cells were significantly smaller than parent cells. This data suggests that cell ‘downsizing’ may be a coping mechanism to allow growth under low cell turgor conditions. Besides, this study also provides a potential non-GM method for designing innovative cheese-making strains.