Evolving understanding of the type VII secretion system in Gram-positive bacteria

While these effectors share minimal sequence homology across T7SSb subtypes and species, WXG100 proteins, WXG100-like SACOL2603 proteins, other small alpha-helical proteins, and LXG toxins are commonly encoded downstream of EssC in T7SSb loci and may share similar functions across systems [2]. [...]more work is needed to confirm secretion of these putative effectors in other Gram-positive organisms to understand their unique contributions to bacterial fitness and host–pathogen interactions. [...]in S. intermedius, LXG toxin TelC (a lipid II phosphatase) mediated killing against S. intermedius strains, Streptococcus pyogenes, and E. faecalis, but not against the Gram-negative organisms tested [3]. Recently, the T7SSb of rhizobacterium Bacillus velezensis was shown to promote iron acquisition and root colonization [11], and the S. aureus T7SSb is regulated by iron availability [2]; thus, the role for T7SSb in nutrient acquisition may be underappreciated. Because of these functions and because the T7SSb also promotes functions such as development of Streptomyces scabies [5], it is hypothesized that the T7SSb may have evolved for housekeeping roles and/or bacterial competition and niche establishment [2]. Interestingly, in S. aureus, T7SSb promotes resistance to host fatty acids [16], as well as modulates cytokine responses and dampens macrophage recruitment during murine blood infection [17], but not in zebrafish [18]. [...]T7SSb-driven immune responses or evasion may depend on the specific effectors secreted by that strain and/or differential regulation of T7SSb loci.