Root‐knot nematodes are destructive phytopathogens that damage agricultural crops globally and there is growing interest in the use of biocontrol based on rhizobacteria such as Bacillus to combat Meloidogyne species. It is hypothesized that nematicidal activity of Bacillus can be attributed to the production of secondary metabolites and hydrolytic enzymes. Yet, few studies have characterized these metabolites and their identities remain unknown. Others are speculative or fail to elaborate on how secondary metabolites were detected or distinguished from primary metabolites. Metabolites can be classified based on their origin as either intracellular or extracellular and based on their function, as either primary or secondary. Although this classification is in general use, the boundaries are not always well defined. An understanding of the secondary metabolite and hydrolytic enzyme classification of Bacillus species will facilitate investigations aimed at bionematicide development. This review summarizes the significance of Bacillus hydrolytic enzymes and secondary metabolites in bionematicide research and provides an overview of known classifications. The importance of appropriate cultivation conditions for optimum metabolite and enzyme production are also discussed. Finally, the use of metabolomics for the detection and identification of nematicidal compounds is considered.

Agricultural crops are severely damaged by root-knot nematodes causing extensive financial losses globally. Historically, agrochemicals have been the preferred method to combat these pests; however, threats to humans and the environment posed by these agrochemicals led to the need for developing new biocontrol agents. Importantly, the latter should adhere to biosafety regulations while being highly effective. Root-knot nematodes live in soil and thus the use of rhizobacteria such as Bacillus for biocontrol development have shown potential. Although various Bacillus species have been tested in this capacity, little is known about their secondary metabolites and the mechanisms of action responsible for their nematicidal activity. If these secondary metabolites can be qualitatively and quantitatively characterised, metabolic features could be synthetically engineered and used to combat root-knot nematodes. Although there is great potential for bionematicides, the commercialisation and development of such products can be difficult. This review summarises the importance of Bacillus species as natural antagonists of root-knot nematodes through the production of secondary metabolites. It provides an overview of the significance of root-knot nematodes in agriculture and the advances of chemical nematicides in recent years. The potential of Bacillus species as biocontrol agents, the known mechanisms of action responsible for the nematicidal activity demonstrated by Bacillus species, non-target effects of biocontrol agents and the commercialisation of Bacillus-based bionematicides are discussed.

Serpentine soils are characterized by nutrient imbalances and high levels of potentially toxic metals (PTMs). These soils host depauperate plant communities of species with specialized adaptations. Initial studies showed that South African serpentine soils harbor distinct biocrust algal and cyanobacterial species compared to adjacent non‐serpentine soils, with these communities further differing based on high and low precipitation levels. Here, we investigated the bacterial and fungal diversity of biological soil crusts from serpentine and non‐serpentine soils at two precipitation levels. The bacterial and fungal communities were characterized using 16S rDNA and ITS metabarcoding, respectively. No significant differences could be found in bacterial richness and community structure. Nevertheless, bacterial taxa such as Archangium , Candidatus Solibacter , Chthoniobacter , and Microvirga were more abundant in serpentine biocrusts or biocrusts receiving lower precipitation. The fungal community structure was distinct between serpentine and non‐serpentine soils ( p = 0.027) and between high and low precipitation ( p = 0.018). Furthermore, fungal diversity was lowest in the drier, serpentine biocrusts compared to non‐serpentine ( p = 0.001) and serpentine crusts receiving higher precipitation ( p = 0.002). The fungal genera, Ramimonilia and Vishniacozyma , which are known to be resistant or tolerant to PTMs and other environmental extremes, were significantly more abundant ( p = 0.036 and p = 0.016, respectively) in serpentine biocrusts, with the latter indicating serpentine habitats. This study concluded that soil type influenced the fungal alpha diversity, specifically in the serpentine soil, resulting in a decrease in fungal species richness. Furthermore, precipitation influenced fungal beta diversity by shaping distinct fungal communities found in the biocrusts of serpentine and non‐serpentine soils.