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Microbes & Immunity Brachyspira pilosicoli novel outer membrane proteins

(PIS) in pigs, and human intestinal spirochetosis (HIS) in osmotic stress and destabilisation when exposed to low-
humans. Spirochetal infections have been reported in the ionic-strength buffers. 22
United Kingdom, continental Europe, Scandinavia, North The B. pilosicoli outer envelope contains
America, Oceania, Iran, Malaysia, and South America. lipooligosaccharides (LOS) rather than lipopolysaccharides
2-7
B. pilosicoli has a broad host range, including dogs, (LPS), exhibiting serological diversity across multiple
8,9
monkeys, water birds, game birds, and humans. 8
23
strains. Bacteria with diderm envelopes possess a
In IS, numerous brachyspiral cells penetrate the mucosal diverse family of OM proteins (OMPs), characterized by
layer overlying enterocytes in the small intestine, attaching b-barrel structures (OMBBs) and LOS. 24,25 β-barrels are
one end to the luminal surface of the enterocytes, aided by protein structures composed of amphipathic, anti-parallel
surface lipoproteins. This attachment forms a distinctive β-strands that close in on themselves, forming a cylindrical
layer resembling a “false brush border.” B. pilosicoli is structure. The β-barrels of OMPs are typically composed of
8
the sole etiological agent of PIS, which is marked by an even number of β-strands, typically ranging from 8 to
diarrhea and impaired growth in pigs. AIS in chickens 36. These β-strands are alternately connected on each side
9,10
26
is associated with the delayed onset of egg laying, wet and of the OM by long loops on the extracellular surface and
bloody feces, reduced growth rate, and diarrhea. 3,8,11 HIS is by shorter turns on the periplasmic side. OMBB proteins
27
associated with a range of non-specific clinical symptoms, are involved in a range of functions, including nutrient
including abdominal pain, altered bowel patterns, chronic acquisition, membrane biogenesis, assembly of OMPs,
diarrhea, and rectal bleeding. 3,12-15 adhesion, biofilm formation, efflux, proteolysis, and pilus
28
Common risk factors for zoonotic transmission formation. Thus, OMBB proteins represent a crucial
of B. pilosicoli to humans include exposure to fecally area of research and a promising target for developing
contaminated water, 9,16-18 rural or animal exposure, antibacterial therapies to combat pathogenic microbes.
overcrowding, socioeconomic depression, travel to less Notably, few OMPs of B. pilosicoli have been studied,
developed countries, immunosuppression due to HIV including BmpC (a 23 kDa lipoprotein), a 45 kDa surface-
22
infection, or being a homosexual male. AIS and PIS are exposed lipoprotein, and Bmp72. Christodoulides
8
29
30
underreported diseases, bearing significant economic et al. employed an in silico reverse vaccinology approach
19
consequences for global food production. Although no to identify potential vaccine candidates from predicted
comprehensive cost analysis for PIS exists, AIS alone is OMBB proteins. Although a few OMPs and lipoproteins of
estimated to cost the poultry industry approximately GBP B. pilosicoli have been identified, 22,29-31 the identification and
18 million annually in the United Kingdom. Extrapolating characterization of the complete OM proteome are needed
3
from these figures, combined global economic losses to to define their potential roles in disease pathogenesis,
both industries could reach approximately USD 1–2 billion particularly in processes such as attachment, virulence,
annually. 19 and eliciting host immune responses.
Antibiotics are used to treat AIS, PIS, and HIS; In this study, a comprehensive in silico approach was
however, resistance has been reported. Antibiotics such employed to identify novel OMBB proteins in B. pilosicoli.
18
as co-amoxicillin and metronidazole are used to treat HIS, A consensus of the outputs from OM localization
whereas pleuromutilins, macrolides, and lincosamides are prediction tools and b-barrel conformation prediction
used for AIS and PIS. Although antibiotics are commonly tools was considered for OMBB protein prediction.
18
used, no vaccines are currently available to prevent HIS, Through stringent screening criteria and manual curation,
AIS, or PIS, highlighting the urgent need for vaccine 42 putative OMBB proteins were selected. In addition,
development. deep-learning-based structural models of the proteins
The reference strain (i.e., B. pilosicoli strain 95/1000) were generated. Structural homologs were identified using
possesses a single circular chromosome of approximately the digital addressable lighting interface (DALI) server and
2.59 Mb and lacks any extrachromosomal elements. The Foldseek tool, revealing the functional roles of the proteins.
B. pilosicoli genome comprises 2338 genes, with coding Furthermore, sequence-based annotations were performed
regions accounting for approximately 85% of the total using PANNZER and eggNOG-mapper. Amino acid
genome. Like other Gram-negative bacteria, B. pilosicoli sequence variations in the predicted proteins were obtained
20
consists of a central protoplasmic cylinder enclosed by a from nine strains of B. pilosicoli and mapped onto the
membrane sheath known as the outer membrane (OM). structural models. This study identified a total of 42 OMBB
21
The exact composition of B. pilosicoli’s OM is not fully proteins of B. pilosicoli, computationally characterized
understood; however, it is known to be extremely labile due their structure and function, and identified peptide regions
to its high sterol content, which results in low resistance to potentially crucial for bacterial pathogenesis.

Volume 2 Issue 4 (2025) 80 doi: 10.36922/MI025230050