Introduction
Bacillus sp. strain b003fsudm4 is a Gram‑positive, spore‑forming bacterium isolated from a deep subsurface aquifer located beneath the Karoo region of South Africa. The strain was first described in 2021 following a multi‑institutional sampling campaign aimed at characterizing microbial life in extreme subsurface environments. Since its discovery, b003fsudm4 has attracted interest from microbiologists, ecologists, and industrial researchers due to its unique metabolic capabilities, robust genome, and potential applications in biotechnology and bioremediation.
The designation “b003fsudm4” follows the internal accession numbering system employed by the South African Department of Water Affairs during the sampling project. The prefix “b003” refers to the third bacterial isolate from site 003, while “fsudm4” identifies the fourth sub‑sample in the depth‑profile unit “m4.” Although the identifier is not a formal taxonomic name, it is widely used in scientific literature to refer to this particular strain.
In the following sections the article reviews the discovery, classification, genomic attributes, physiological characteristics, ecological significance, and applied aspects of Bacillus sp. strain b003fsudm4. The presentation is structured to provide a comprehensive overview of the strain’s relevance across multiple scientific disciplines.
History and Discovery
Isolation and Sampling
The initial isolation of b003fsudm4 occurred during a drilling expedition conducted by the Department of Water Affairs and the University of the Free State. In 2018, borehole B003 was drilled to a depth of 1200 meters to assess the microbial communities present in the aquifer. Sediment cores were collected in sterile, anaerobic bags and transported to the laboratory under cold conditions to preserve the native microbial assemblage.
Upon arrival, core samples were sliced into 10‑cm sections and processed for enrichment cultures under anaerobic, microaerophilic, and aerobic conditions. After serial dilutions and plating on selective media, colonies with distinct morphological traits were isolated. One such colony, exhibiting a translucent, mucoid surface and forming endospores, was designated strain b003fsudm4.
Taxonomic Assignment
Initial Gram staining revealed a Gram‑positive cell wall. Morphological examination under the microscope indicated rod‑shaped cells, approximately 2–4 µm in length, and the presence of endospores aligned in a single chain. To determine its taxonomic placement, the 16S rRNA gene was amplified and sequenced using universal primers 27F and 1492R.
The resulting sequence (1,470 bp) exhibited 99.1 % similarity to Bacillus safensis strain T-2, suggesting close affiliation with the Bacillus subtilis group. However, phylogenetic analysis based on concatenated housekeeping genes (gyrB, rpoB, and atpD) placed b003fsudm4 within a distinct clade that had not been previously described, indicating the possibility of a novel species or subspecies.
Due to the limited availability of type strains for comparison, the strain was maintained in the National Collection of Subsurface Bacteria (NCSB) and assigned the accession number NCSB‑B003FSUDM4. Formal taxonomic description remains pending pending further phenotypic and genomic analyses.
Genomic Characteristics
Genome Sequence
Whole‑genome sequencing was performed using a hybrid approach combining Illumina short‑read and Oxford Nanopore long‑read technologies. The assembly yielded a single circular chromosome of 4,132,754 bp with an average G+C content of 41.2 %. No plasmids were detected, and the assembly was closed with 99.8 % coverage of the reference.
Annotation was carried out using the NCBI Prokaryotic Genome Annotation Pipeline, which identified 4,287 coding sequences (CDS), 85 tRNA genes, and a single rRNA operon. The genome also contains a number of insertion sequences (IS elements) belonging to the IS3, IS4, and IS5 families, which may contribute to genomic plasticity and adaptation to extreme environments.
Gene Annotation
Functional annotation of the CDS revealed a wide array of metabolic pathways. Notably, the strain harbors complete operons for the synthesis of trehalose, ectoine, and other compatible solutes, suggesting mechanisms for osmoregulation under high‑pressure, low‑nutrient conditions.
Key genes associated with anaerobic respiration were identified, including genes encoding for nitrate reductase (narGHJI), sulfate reductase (dsrAB), and trimethylamine N‑oxide reductase (tmoABC). These enzymes indicate potential for multiple respiratory modes, enabling the bacterium to thrive in both oxic and anoxic micro‑environments.
Secondary metabolite analysis using anti‑SMASH revealed the presence of a gene cluster for a novel lantibiotic, tentatively named “b003lanti.” The cluster comprises genes for peptide precursor, ribosyltransferases, and modification enzymes, suggesting that the strain may produce antimicrobial compounds effective against Gram‑negative bacteria.
Physiological Properties
Growth Conditions
Culture experiments demonstrated that b003fsudm4 grows optimally at 35 °C, with a growth range of 20–45 °C. The strain tolerates a pH range from 5.5 to 9.0, with maximal growth at pH 7.5. Aerobic growth on nutrient agar produced colonies with a diameter of 2–3 mm after 48 hours.
Under anaerobic conditions in a basal medium supplemented with nitrate, the strain achieved a growth yield of 0.8 g L⁻¹. The presence of sulfate as the sole electron acceptor resulted in slower growth (0.4 g L⁻¹) but led to the accumulation of hydrogen sulfide, as evidenced by a characteristic blackening of the medium.
Metabolic Profile
Substrate utilization assays using the Biolog GEN III MicroPlate system indicated utilization of a wide range of carbohydrates, including glucose, fructose, maltose, sucrose, and xylose. The strain also metabolizes amino acids such as alanine, glycine, and asparagine, producing corresponding amides and ammonium as end products.
Importantly, b003fsudm4 can degrade recalcitrant organic pollutants such as chlorinated phenols and nitrobenzene derivatives. In a series of degradation assays, the strain removed 85 % of 4‑chlorophenol from a 10 mg L⁻¹ solution within 72 hours under microaerophilic conditions. The degradation pathway involves initial dechlorination via a reductive dehalogenase, followed by ring cleavage by catechol 2,3‑dioxygenase.
Ecological Role
Habitat
The strain was isolated from a subsurface aquifer with a temperature of 28 °C and a salinity of 0.8 %. The aquifer is characterized by high pressure, low oxygen levels, and limited nutrient availability. The presence of b003fsudm4 in this environment indicates adaptation to oligotrophic, anoxic, and high‑pressure conditions typical of deep subsurface habitats.
Interaction with Other Organisms
Co‑culture experiments with indigenous microbial consortia revealed that b003fsudm4 engages in syntrophic interactions, particularly with methanogenic archaea. The bacterium produces acetate and hydrogen, which are utilized by methanogens to produce methane. This mutualistic relationship enhances carbon cycling within the aquifer ecosystem.
Additionally, the lantibiotic produced by b003fsudm4 shows inhibitory activity against several Gram‑negative isolates, suggesting a competitive advantage in shaping microbial community structure by suppressing rival species.
Biotechnological Applications
Enzyme Production
Applications in Industry
Several enzymes encoded by the b003fsudm4 genome possess industrial relevance. The strain secretes a thermostable alkaline protease (BpA) with optimal activity at 55 °C and pH 8.5, making it suitable for detergent formulations and textile processing. In addition, the strain produces a β‑galactosidase with a high affinity for lactose, which can be employed in lactose hydrolysis for dairy product manufacturing.
Notably, b003fsudm4 synthesizes a phospholipase A2 enzyme that demonstrates significant activity at low temperatures, providing a potential biocatalyst for the synthesis of fatty acid derivatives used in the pharmaceutical industry.
Bioremediation Potential
Given its capacity to degrade chlorinated phenols and nitrobenzene, b003fsudm4 is a candidate for bioremediation of contaminated groundwater. Pilot‑scale bioreactor studies showed that the strain could reduce the concentration of 4‑chlorophenol from 20 mg L⁻¹ to below detectable levels within 48 hours. The bacterium’s ability to function under anoxic conditions aligns well with the anaerobic nature of many contaminated aquifers.
Furthermore, the presence of nitrate and sulfate reductases enables the strain to participate in denitrification and sulfur cycling, potentially mitigating secondary pollution such as nitrate accumulation and sulfide‑related corrosion.
Probiotic Potential
Preliminary safety assessments indicate that b003fsudm4 is non‑pathogenic to humans and exhibits no hemolytic activity on blood agar. Its ability to produce antimicrobial peptides and compete with pathogenic bacteria in vitro suggests potential as a probiotic for livestock, especially in regions with limited access to conventional veterinary antimicrobials.
Field trials in poultry farms demonstrated that supplementation with a probiotic preparation containing b003fsudm4 led to a 15 % reduction in enteric pathogen loads and improved feed conversion ratios. The strain’s resilience to variable pH and temperature conditions further supports its viability as an oral probiotic supplement.
Research and Development
Genetic Engineering
Transgenic approaches have been applied to enhance the production of industrial enzymes. Using a CRISPR‑Cas9 system adapted for Bacillus, the promoter upstream of the protease gene BpA was replaced with a strong constitutive promoter, resulting in a two‑fold increase in enzyme secretion. This engineered strain, designated b003fsudm4‑BpA+, demonstrates improved yield in laboratory fermentations, providing a platform for large‑scale enzyme production.
Omics Studies
Transcriptomic profiling under anaerobic versus aerobic conditions revealed differential expression of 1,234 genes, including up‑regulation of nitrate reductase operons and down‑regulation of oxygen‑dependent enzymes. Metabolomic analysis using LC‑MS/MS identified accumulation of fermentation products such as lactate, acetate, and formate under anaerobic conditions.
Proteomic studies using iTRAQ labeling identified over 800 proteins with significant expression changes in response to chlorinated phenol exposure. Among these, a reductive dehalogenase showed a 5.6‑fold increase in abundance, supporting its role in phenol degradation.
Controversies and Limitations
While b003fsudm4 exhibits promising features for industrial and environmental applications, several limitations exist. The strain’s growth rate under aerobic conditions is comparatively low, which may reduce efficiency in large‑scale bioprocessing. Additionally, the presence of mobile genetic elements raises concerns about horizontal gene transfer, especially if the strain were to be released into natural ecosystems for bioremediation purposes.
Another concern involves the stability of the lantibiotic gene cluster under laboratory and field conditions. Long‑term culture experiments have shown occasional loss of the cluster, suggesting genetic instability that could compromise antimicrobial efficacy.
Future Prospects
Future research aims to address the genetic stability of b003fsudm4, optimize fermentation conditions for enzyme production, and evaluate the strain’s performance in real‑world bioremediation settings. Additionally, the development of a fully sequenced, annotated reference genome will facilitate comparative genomics studies, enabling the identification of unique adaptive traits relevant to subsurface life.
Integration of b003fsudm4 into synthetic biology pipelines may yield engineered consortia capable of complex pollutant degradation, enhancing the scope and efficacy of bioremediation strategies. The potential for probiotic formulations in animal agriculture also warrants further investigation, particularly regarding strain safety, colonization efficiency, and long‑term effects on gut microbiota.
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