Effects Of Lytic Transglycosylases On β-lactams Resistance In Shewanella Oneidensis

Shewanella oneidensis is facultive anaerobic y-proteobacterium which is known for its diverse respiratory substrates. Apart from this, S. oneidensis possess native re-sistance against multiple β-lactams. In our former research, we found β-lactamase BlaA is the major contributor for the resistance. In Escherichia coli, lytic transglycosylases can release small molecules (peptidoglycan components) functioned to activate the expression of blaA, so their deletion would result in low resistance to β-lactams. In this paper some researchs were did in order to explore the role lytic transglycosylases played in the expression of blaA. The results were as follows:In S. oneidensis, there were seven LTs; they were SltY, MltBl, MltB2, MltC, MltD1, MltD2, and MltF。In this study, we found there were no changes in phenotype between all mutants and wild-type strain; however deletion of MltB1, MltB2, SltY and MltF could result in defective growth.In contrast with E. coli, mutants of mltBl, mltB2 and sltY gained enhanced β-lactams resistance in S. oneidensis. Experimental results showed BlaA was corre-lated with enhanced β-lactams resistance. Further study showed P-lactams resistance was additive in the ΔmltBlΔmltB2 and ΔmltB2ΔsltY strains,.Given the results we got from expression of LTs in wild-type, we thought LTs play different role in growth and blaA expression.MltF and MltB1 played important role in cell growth and blaA expression respectively, MltB2 and SltY had affection on both progress.In our previous study, ΔmrcA and AampG displayed similar levels of resistance to three different tested β-lactams. However there were differences between their blaA expression. The basal levels of BlaA activity were constitutively robust in the AmrcA strain, contrasting with the relatively low but inducible levels in the AampG strain. Given this, we further explored whether expression of blaA in mutants of LTs was mediated by MrcA and AmpGIn this study, we found blaA coluld be induced in the ΔmltB2ΔsltYΔmrcA strain but not in the ΔmltBlΔmltB2ΔmrcA strain. Apart from this, we also found the BlaA activities in the ΔsltYΔmrcA strain were comparable to those in the ΔmrcA strain, so MltB1 and MltB2 may play important but different role in the expression of blaA. We also found both ΔmltB1ΔmltB2ΔampG and ΔmltB2ΔsltYΔampG strains had higher BlaA activity than corresponding ΔmltBlΔmltB2, ΔmltB2ΔsltY and AampG strains, so it indicated that products of MltB1, MltB2 and SltY may entered into the cytoplasm through AmpG and play inhibitory role in the expression of blaA.