PgFur participates differentially in expression of virulence factors in more virulent A7436 and less virulent ATCC 33277 Porphyromonas gingivalis strains

Abstract

Background Porphyromonas gingivalis is considered a keystone pathogen responsible for chronic periodontitis. Although several virulence factors produced by this bacterium are quite well characterized, very little is known about regulatory mechanisms that allow different strains of P. gingivalis to efficiently survive in the hostile environment of the oral cavity, a typical habitat characterized by low iron and heme concentrations. The aim of this study was to characterize P. gingivalis Fur homolog (PgFur) in terms of its role in production of virulence factors in more (A7436) and less (ATCC 33277) virulent strains. Results Expression of a pgfur depends on the growth phase and iron/heme concentration. To better understand the role played by the PgFur protein in P. gingivalis virulence under low- and high-iron/heme conditions, a pgfur -deficient ATCC 33277 strain (TO16) was constructed and its phenotype compared with that of a pgfur A7436-derived mutant strain (TO6). In contrast to the TO6 strain, the TO16 strain did not differ in the growth rate and hemolytic activity compared with the ATCC 33277 strain. However, both mutant strains were more sensitive to oxidative stress and they demonstrated changes in the production of lysine- (Kgp) and arginine-specific (Rgp) gingipains. In contrast to the wild-type strains, TO6 and TO16 mutant strains produced larger amounts of HmuY protein under high iron/heme conditions. We also demonstrated differences in production of glycoconjugates between the A7436 and ATCC 33277 strains and we found evidence that PgFur protein might regulate glycosylation process. Moreover, we revealed that PgFur protein plays a role in interactions with other periodontopathogens and is important for P. gingivalis infection of THP-1-derived macrophages and survival inside the cells. Deletion of the pgfur gene influences expression of many transcription factors, including two not yet characterized transcription factors from the Crp/Fnr family. We also observed lower expression of the CRISPR/Cas genes. Conclusions We show here for the first time that inactivation of the pgfur gene exerts a different influence on the phenotype of the A7436 and ATCC 33277 strains. Our findings further support the hypothesis that PgFur regulates expression of genes encoding surface virulence factors and/or genes involved in their maturation. Electronic supplementary material The online version of this article (10.1186/s12866-019-1511-x) contains supplementary material, which is available to authorized users.

PgRsp Is a Novel Redox-Sensing Transcription Regulator Essential for Porphyromonas gingivalis Virulence

“…Recently, we have shown that P. gingivalis ferric uptake regulator homolog (PgFur) is an important transcription factor, regulating genes involved in interaction with host cells and other periodontopathogens [13,16]. A P. gingivalis mutant strain lacking a pgfur gene showed reduced tolerance to H 2 O 2 and was more sensitive to air exposure, although we did not observe regulation of typical genes responsible for the oxidative stress response [13,16].…”

“…Prevotella intermedia strain 17 (GenBank: CP003502.1 and CP003503.1) and Tannerella forsythia (ATCC 43037) were maintained as described previously [37]. Streptococcus gordonii (ATCC 10558) was grown in TSB agar or liquid medium (5% TBS) under an increased concentration of CO 2 using the Atmosphere generation system (Thermo Scientific, Waltham, MA, USA) as reported previously [16].…”

“…Gene expression was initially examined in bacteria cultured for 20 h in iron/heme rich (Hm) or depleted (DIP) medium using microarray analysis as reported previously [13,16]. Additionally, reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) was used as reported previously [16,40].…”

“…P. gingivalis has developed numerous sophisticated mechanisms for the acquisition of nutrients, enabling its survival as well as its proliferation inside and spread between host cells [12][13][14][15][16]. Among the most important virulence factors are proteases, mainly lysine-and arginine-specific gingipains encoded by kgp, rgpA, and rgpB genes, which play a crucial role in the degradation of host proteins and tissue components [17][18][19].…”

“…Recently, we have shown that P. gingivalis ferric uptake regulator homolog (PgFur) is an important transcription factor, regulating genes involved in interaction with host cells and other periodontopathogens [13,16]. A P. gingivalis mutant strain lacking a pgfur gene showed reduced tolerance to H 2 O 2 and was more sensitive to air exposure, although we did not observe regulation of typical genes responsible for the oxidative stress response [13,16]. We discovered that the expression of many genes involved in regulation of gene expression was altered in the mutant strain, including the downregulated PGA7_00004090 gene, encoding a putative transcription factor belonging to the cAMP receptor protein/fumarate and nitrate reductase regulator (Crp/Fnr) superfamily.…”