Bridging the Gap: Type III Secretion Systems in Plant-Beneficial Bacteria

Type III secretion systems (T3SSs) are bacterial membrane-embedded nanomachines translocating effector proteins into the cytoplasm of eukaryotic cells. They have been intensively studied for their important roles in animal and plant bacterial diseases. Over the past two decades, genome sequencing has unveiled their ubiquitous distribution in many taxa of Gram-negative bacteria, including plant-beneficial ones. Here, we discuss the distribution and functions of the T3SS in two agronomically important bacterial groups: the symbiotic nodule-forming nitrogen-fixing rhizobia and the free-living plant-beneficial Pseudomonas spp. In legume-rhizobia symbiosis, T3SSs and their cognate effectors play important roles, including the modulation of the plant immune response and the initiation of the nodulation process in some cases. In plant-beneficial Pseudomonas spp., the roles of T3SSs are not fully understood, but pertain to plant immunity suppression, biocontrol against eukaryotic plant pathogens, mycorrhization facilitation, and possibly resistance against protist predation. The diversity of T3SSs in plant-beneficial bacteria points to their important roles in multifarious interkingdom interactions in the rhizosphere. We argue that the gap in research on T3SSs in plant-beneficial bacteria must be bridged to better understand bacteria/eukaryotes rhizosphere interactions and to support the development of efficient plant-growth promoting microbial inoculants.

Biosorption and Bioleaching of Heavy Metals from Electronic Waste Varied with Microbial Genera

Industrialization and technological advancements have led to the exploitation of natural resources and the production of hazardous wastes, including electronic waste (E-waste). The traditional physical and chemical techniques used to combat E-waste accumulation have inherent drawbacks, such as the production of harmful gases and toxic by-products. These limitations may be prudently addressed by employing green biological methods, such as biosorption and bioleaching. Therefore, this study was aimed at evaluating the biosorption and bioleaching potential of seven microbial cultures using E-waste (printed circuit board (PCB)) as a substrate under submerged culture conditions. The cut pieces of PCB were incubated with seven microbial cultures in liquid broth conditions in three replicates. Atomic absorption spectroscopy (AAS) analysis of the culture biomass and culture filtrates was performed to evaluate and screen the better-performing microbial cultures for biosorption and bioleaching potentials. The best four cultures were further evaluated through SEM, energy-dispersive X-ray spectroscopy (EDX), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) studies to identify the possible culture that can be utilized for the biological decontamination of E-waste. The study revealed the highest and differential ability of Pleurotus florida and Pseudomonas spp. for biosorption and bioleaching of copper and iron. This can be attributed to bio-catalysis by the laccase enzyme. For both P. florida and Pseudomonas spp. on the 20th day of incubation, laccase exhibited higher specific activity (6.98 U/mg and 5.98 U/mg, respectively) than other microbial cultures. The biomass loaded with Cu2+ and Fe2+ ions after biosorption was used for the desorption process for recovery. The test cultures exhibited variable copper recovery efficiencies varying between 10.5 and 18.0%. Protein characterization through SDS-PAGE of four promising microbial cultures exhibited a higher number of bands in E-waste as compared with microbial cultures without E-waste. The surface topography studies of the E-waste substrate showed etching, as well as deposition of vegetative and spore cells on the surfaces of PCB cards. The EDX studies of the E-waste showed decreases in metal element content (% wt/% atom basis) on microbial treatment from the respective initial concentrations present in non-treated samples, which established the bioleaching phenomenon. Therefore, these microbial cultures can be utilized to develop a biological remediation method to manage E-waste.

The BIOHERBICIDAL ACTIVITY OF Pseudomonas SPP (PF-097) To SUPRESS THE ALLELOPATHIC STRESS OF Trianthema portulacastrum LEAF EXTRACT ON Vigna mungo

Vigna mungo L. (black gram) is a summer pulse crop endemic to Central Asia. It is one of Pakistan's top five premium food beans and a highly cost-effective crop. Allelochemicals in Trianthema portulacastrum leaf extract effect and inhibit black gram germination rate, seedling length, fresh and dry biomass of seedling from low to high concentrations. The research revealed that in vitro leaf extract of black pigweed decrease the mash bean leaf germination percentage (34% to 6%), seedling length (10cm to 3cm), fresh biomass of seedling (2.4g to 0.94g), dry biomass (1.2g to 0.47g). Biological tool Pseudomonas (PF- 097) act as bioherbicide and as plant growth promoter agent (PGPR) to decrease the Trianthema portulacastrum allelopathic stress and to enhance the growth of black gram. The Pseudomonas (PF-097) PGPR addition in vitro experiment increased mash bean leaf germination (8-42%), seedling length (12-54%), and fresh biomass of seedling (8-17%) and dry biomass of seedling (0.47g-1.2g). In vivo experimental study revealed that whole plant material of black pigweed significantly suppress the shoot length (46cm to 18cm), shoot fresh biomass (2.6g to 0.66g) and shoot dry biomass (1.31g to 0.33g) and Pseudomonas (PF-097) PGPR incorporation in vivo experminet significantly increased the shoot length (4% to 12%), shoot fresh biomass (18% to 35%), shoot dry biomass (17% to 35%). Physiological activity of Catalase and peroxidase considerably increased in negative treatments amended with only T. portulacastrum and decreased in positive treatments by using biological agent Pseudomonas spp (PF- 097). By the amendment of Pseudomonas (PF- 097) protein content of mash bean seedling was significantly increased in positive treatments as compared to negative treatments.

Comparative study on the microbiological quality of vegetables collected from local markets and super shops of Dhaka city

Vegetables are major source of vitamins and fibers but presence of pathogens in salad vegetables can cause outbreak of diseases. Several studies have been conducted on commonly consumed vegetables so far to detect the level of microbial contamination. However, few of them compare the microbial quality of local and super shop vegetables. The present study was conducted for microbiological assessment and comparing four types of vegetables collected from two different market conditions. In this study, Green chili (Capsicum frutescens L.), Tomato (Solanum lycopersicum), Coriander (Coriandrum sativum) and Lady’s finger (Abelmoschus esculentus) were analyzed to determine Total Viable Bacterial (TVB) Counts, Total Fungal (TF) Counts, Total Coliform Counts (TCC), Total Fecal Coliform (TFC) Counts and occurrence of Staphylococcus aureus, Pseudomonas spp., Listeria spp., Bacillus spp., Salmonella spp., and Vibrio spp. Among these microorganisms, Klebsiella spp. and Pseudomonas spp. were significantly present in coriander of both local market and super shop. All pathogenic bacteria and fungi were found in huge amounts in the vegetable samples of the local market. Although some pathogenic bacteria and fungi were also found in the same samples of the super shop, relatively lower than the local market’s vegetables. In conclusion, contamination in collected vegetable samples were not acceptable but comparatively higher load in local market samples indicated that the hygienic condition in these markets is not sufficiently maintained. Stamford Journal of Microbiology, Vol.11 (1) 2021: 24-27

The Application of Bacillus subtilis for Adhesion Inhibition of Pseudomonas and Preservation of Fresh Fish

Inhibiting the growth of spoilage bacteria, such as Pseudomonas spp., is key to reducing spoilage in fish. The mucus adhesion test in vitro showed that the adhesion ability of Bacillus subtilis was positively correlated with its inhibition ability to Pseudomonas spp. In vivo experiments of tilapia showed that dietary supplementation with B. subtilis could reduce the adhesion and colonization of Pseudomonas spp. in fish intestines and flesh, as well as reduce total volatile basic nitrogen (TVB-N) production. High throughput and metabolomic analysis showed treatment with B. subtilis, especially C6, reduced the growth of Pseudomonas spp., Aeromonas spp., Fusobacterium spp., and Enterobacterium spp., as well as aromatic spoilage compounds associated with these bacteria, such as indole, 2,4-bis(1,1-dimethylethyl)-phenol, 3-methyl-1-butanol, phenol, and 1-octen-3-ol. Our work showed that B. subtilis could improve the flavor of fish by changing the intestinal flora of fish, and it shows great promise as a microecological preservative.

Antagonistic activity of rice rhizosphere isolates against Xanthomonas oryzae pv. oryzae bacterial blight pathogen

Attempts were made to isolate beneficial bio agents from rice rhizosphere which resulted in isolation of 46 Bacillus spp and 15 fluorescent Pseudomonas spp which were further investigated for their potential aginst BB of rice diseaseAmong twenty six isolates of Bacillus, two isolates were most antagonistic and showed highest inhibition percentage (57.09) The potential isolates of Pseudomonas (P-4, P-5, P-6, P-7 and P-8), Bacillus (ARI 1-2, ARI 2-4, ARI 1-3, D1-1-2 and D2-1-1) were tested in vivo under glass house conditions for antagonism against Xoo which revealed that P-7 was effective in reduction of lesion length (18.5cm) when compared to control (20.37cm). The potential isolates of Pseudomonas (P-4, P-5, P-6, P-7 and P-8), Bacillus (ARI 1-2, ARI 2-4, ARI 1-3, D1-1-2 and D2-1-1) were tested in vivo under glass house conditions for antagonism against Xoo which revealed that P-7 was effective in reduction of lesion length (18.5cm) when compared to control (20.37cm). The present study indicated that PGPR isolates P-4, P-6, P-7 and P-8 can be used as biofertilizers, which will add up for enhanced growth of rice.

In Tuber Biocontrol of Potato Late Blight by a Collection of Phenazine-1-Carboxylic Acid-Producing Pseudomonas spp.

Phenazine-1-carboxylic acid (PCA) produced by plant-beneficial Pseudomonas spp. is an antibiotic with antagonistic activities against Phytophthora infestans, the causal agent of potato late blight. In this study, a collection of 23 different PCA-producing Pseudomonas spp. was confronted with P. infestans in potato tuber bioassays to further understand the interaction existing between biocontrol activity and PCA production. Overall, the 23 strains exhibited different levels of biocontrol activity. In general, P. orientalis and P. yamanorum strains showed strong disease reduction, while P. synxantha strains could not effectively inhibit the pathogen’s growth. No correlation was found between the quantities of PCA produced and biocontrol activity, suggesting that PCA cannot alone explain P. infestans’ growth inhibition by phenazine-producing pseudomonads. Other genetic determinants potentially involved in the biocontrol of P. infestans were identified through genome mining in strains displaying strong biocontrol activity, including siderophores, cyclic lipopeptides and non-ribosomal peptide synthase and polyketide synthase hybrid clusters. This study represents a step forward towards better understanding the biocontrol mechanisms of phenazine-producing Pseudomonas spp. against potato late blight.

Investigative Study on the Bacteriological, Physical and Chemical Profiles of Aquaculture Waters: Insights Into Health Hazards for Fish and Human

Bacteriological and physic-chemical analysis of fish pond water is very important in aquaculture as this gives insights into likely threats to aquaculture and associated personnels. Bacteriological and physico-chemical profiles of selected fish ponds in the Ilorin West area of Kwara State, Nigeria were investigated to evaluate the water quality of rearing enclosures. Physico-chemical analyses revealed quality parameters were within the recommended range for aquaculture. Following bacteriological analyses of static water pond culture, the TVC and TCC showed temporal variations with concentration increasing with sampling time. However, the FCC showed fluctuation. Totally, 8 bacteria groups were isolated from both rearing enclosures. Of these, Gram negative bacteria showed dominance. In which 5 Gram negative (Escherichia coli, Proteus spp, Serratia spp, Enterobacter spp and Pseudomonas spp) and 3 Gram positive (Staphylococcus spp, Streptococcus spp, and Bacillus spp) were encountered. Estimates of bacteria occurrence in both rearing facilities respectively gave: Staphylococcus spp (20%), Streptococcus spp (12%) Proteus spp (8%) Enterobacter spp (20%) Serratia spp (16%), Bacillus spp (9%), Escherichia coli (8%), Pseudomonas spp (7%) from earthen pond water sampled. While Staphylococcus spp (18%), Streptococcus spp (16%), Proteus spp (8%), Enterobacter spp (22%), Serratia spp (8%), Bacillus spp (15%), Escherichia coli (8%), Pseudomonas spp (6%) from concrete water sampled. Conclusively, although there is the presence of bacteria groups of public health concern, the static water exchange provides benefits of natural processing of wastes and restoration of the pond ecosystem. Notably, the presence of Escherichia coli gives indication of presence of pathogenic organisms of enteric origin. The presence of these organisms has been associated with a lack of tentative pond management and effective biosecurity procedures. One recommendation to this culture system (static water aquaculture) is the consideration of adaptation of concepts in biomimicry or biofloc technology which operates on similar principles.

Assessment of Microbiological Quality Associated with Ready- to- Eat Bush Meat Sold at Rumuokoro Market in Rivers State

The study was carried out to investigate the Microbiological quality of microorganisms associated with ready-to-eat bush meat sold at Rumuokoro market in Rivers state. Totally 24 samples were collected and analyzed using different media such as Nutrient agar for Total aerobic plate count (TAPC), MacConkey agar for the coliform count, Eosin methylene blue for Escherichia coli (EC), and Potato Dextrose Agar for Fungal count (FC) and ten (10) fold serial dilution was used. Staphylococcus spp, Pseudomonas spp, Bacillus spp, and Escherichia coli were isolated. The total aerobic plate count (TAPC), E. coli count (EC)-Coliform count (CC), and Fungal count (FC) isolated from antelope were higher when compared to grass-cutter so there was a significant difference (P <0.005). The occurrence of Staphylococcus aureus isolated from antelope (26.9%) was higher when compared to grass- cutter (25.0%). However the occurrence of Pseudomonas spp and Bacillus spp isolated from Antelope (23.1% and 30.8%) were higher when compared to grass- cutter (12.5% and 18.5%) while the occurrence of the above organisms isolated on both Antelope is significantly difference (P<0.005) from grass cutter. But the occurrence of Aspergillus spp and Penicillium spp were higher in grass cutter sample (57.1%) and (42.9%) compared to antelope (55.6%) and (44.4%) respectively, although the mean difference was statistically significant (P<0.005) so there was significant difference. It is hereby recommended that most handlers should always wash hands before and after handling the meat as improper hand washing is the number one cause of food borne illness. Consumers of such meat should learn food hygiene practices such as, soaking the meat in warm salt solution, proper washing and well cooked before consumption.