The GerW protein is essential for L-alanine-stimulated germination of Bacillus subtilis spores

Insights into effects of salt stress on the oil-degradation capacity, cell response, and key metabolic pathways of Bacillus sp. YM1 isolated from oily food waste compost

A novel bacterial strain, Bacillus sp. YM1, was isolated from compost for the efficient degradation of oily food waste under salt stress. The strain's lipase activity, oil degradation ability, and tolerance to salt stress were evaluated in a liquid medium. Additionally, the molecular mechanisms (including key genes and functional processes) underlying the strain's salt-resistant degradation of oil were investigated based on RNA-Seq technology. The results showed that after 24 h of microbial degradation, the degradation rate of triglycerides in soybean oil was 80.23% by Bacillus sp. YM1 at a 30 g L-1 NaCl concentration. The metabolizing mechanism of long-chain triglycerides (C50-C58) by the YM1 strain, especially the biodegradation rate of triglycerides (C18:3/C18:3/C18:3), could reach 98.65%. The most substantial activity of lipase was up to 325.77 U·L-1 at a salinity of 30 g L-1 NaCl. During salt-induced stress, triacylglycerol lipase was identified as the crucial enzyme involved in oil degradation in Bacillus sp. YM1, and its synthesis was regulated by the lip gene (M5E02_13495). Bacillus sp. YM1 underwent adaptation to salt stress through various mechanisms, including the accumulation of free amino acids, betaine synthesis, regulation of intracellular Na+/K+ balance, the antioxidative response, spore formation, and germination. The key genes involved in Bacillus sp. YM1's adaptation to salt stress were responsible for the synthesis of glutamate 5-kinase, superoxide dismutase, catalase, Na+/H+ antiporter, general stress protein, and sporogenic proteins belonging to the YjcZ family. Results indicated that the isolated strain of Bacillus sp. YM1 could significantly degrade oil in a short time under salt stress. This study would introduce new salt-tolerant strains for coping with the biodegradation of oily food waste and provide gene targets for use in genetic engineering.

Microbial Biomass and Enzymatic Activity of the Surface Microlayer and Subsurface Water in Two Dystrophic Lakes

Nutrient and organic matter concentration, microbial biomass and activities were studied at the surface microlayers (SML) and subsurface waters (SSW) in two small forest lakes of different water colour. The SML in polyhumic lake is more enriched with dissolved inorganic nitrogen (0.141 mg l-1) than that of oligohumic lake (0.124 mg l-1), the former also contains higher levels of total nitrogen (2.66 mg l-1). Higher activities of lipase (Vmax 2290 nmol l-1 h-1 in oligo- and 6098 in polyhumic) and glucosidase (Vmax 41 nmol l-1 h-1 in oligo- and 49 in polyhumic) were in the SMLs in both lakes. Phosphatase activity was higher in the oligohumic SML than in SSW (Vmax 632 vs. 339 nmol l-1 h-1) while in polyhumic lake was higher in SSW (Vmax 2258 nmol l-1 h-1 vs. 1908 nmol l-1 h-1). Aminopeptidase activity in the SSW in both lakes was higher than in SMLs (Vmax 2117 in oligo- and 1213 nmol l-1 h-1 in polyhumic). It seems that solar radiation does inhibit neuston microbial community as a whole because secondary production and the share of active bacteria in total bacteria number were higher in SSW. However, in the oligohumic lake the abundance of bacteria in the SML was always higher than in the SSW (4.07 vs. 2.69 × 106 cells ml-1) while in the polyhumic lake was roughly equal (4.48 vs. 4.33 × 106 cells ml-1) in both layers. Results may also suggest that surface communities are not supplemented by immigration from bulk communities. The SML of humic lakes may act as important sinks for allochthonous nutrient resources and may then generate considerable energy pools for microbial food webs.

Cell wall as a target for bacteria inactivation by pulsed electric fields

The integrity and morphology of bacteria is sustained by the cell wall, the target of the main microbial inactivation processes. One promising approach to inactivation is based on the use of pulsed electric fields (PEF). The current dogma is that irreversible cell membrane electro-permeabilisation causes the death of the bacteria. However, the actual effect on the cell-wall architecture has been poorly explored. Here we combine atomic force microscopy and electron microscopy to study the cell-wall organization of living Bacillus pumilus bacteria at the nanoscale. For vegetative bacteria, exposure to PEF led to structural disorganization correlated with morphological and mechanical alterations of the cell wall. For spores, PEF exposure led to the partial destruction of coat protein nanostructures, associated with internal alterations of cortex and core. Our findings reveal for the first time that the cell wall and coat architecture are directly involved in the electro-eradication of bacteria.

The GerW protein is not involved in the germination of spores of Bacillus species

Germination of dormant spores of Bacillus species is initiated when nutrient germinants bind to germinant receptors in spores’ inner membrane and this interaction triggers the release of dipicolinic acid and cations from the spore core and their replacement by water. Bacillus subtilis spores contain three functional germinant receptors encoded by the gerA, gerB, and gerK operons. The GerA germinant receptor alone triggers germination with L-valine or L-alanine, and the GerB and GerK germinant receptors together trigger germination with a mixture of L-asparagine, D-glucose, D-fructose and KCl (AGFK). Recently, it was reported that the B. subtilis gerW gene is expressed only during sporulation in developing spores, and that GerW is essential for L-alanine germination of B. subtilis spores but not for germination with AGFK. However, we now find that loss of the B. subtilis gerW gene had no significant effects on: i) rates of spore germination with L-alanine; ii) spores’ levels of germination proteins including GerA germinant receptor subunits; iii) AGFK germination; iv) spore germination by germinant receptor-independent pathways; and v) outgrowth of germinated spores. Studies in Bacillus megaterium did find that gerW was expressed in the developing spore during sporulation, and in a temperature-dependent manner. However, disruption of gerW again had no effect on the germination of B. megaterium spores, whether germination was triggered via germinant receptor-dependent or germinant receptor-independent pathways.