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Manipulation of rhizosphere microbiome by Microbacterium sp. GB16_1_BI to promote plant growth.

AIM: The bioinoculant properties of a newly identified ammonium-releasing novel strain of Actinomycetota-Microbacterium bengalense sp. nov. GB16_1_BI (Accession number: SRX9280401) on the microbiome structure of rice rhizosphere were assessed. METHODS AND RESULT: GB16_1_BI may inhibit most bacteria present in the rice rhizosphere as well as encouraged the growth of rare bacteria specific to the waterlogged rice rhizosphere. The genome sequence as well as untargeted metabolome analyses of GB16_1_BI showed abundance of secondary metabolites with probable antimicrobial activity. Amplicon sequencing of the 16S rRNA V3-V4 region from the rhizosphere of the black rice showed inhibition of most bacteria by GB16_1_BI. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt2) analysis showed increased abundance in the marker genes for nitrogen cycling (nifH, nrfA, and nrt) but not for nifD or nifK, which was also reflected in the ANOSIM analysis in the OTUs of the N-fixing bacteria. Higher abundance of the nitrogen-fixing methanotrophs, Methylosinus and Methylocystis in inoculated plants also led to study of the marker genes for methane metabolism. CONCLUSION: Microbes present in the rhizosphere contribute to the biogeochemical cycle by transforming unavailable minerals and by retaining nutrients for their growth, which get released after death for plant adsorption. However, not all microbes contribute positively to plant growth. Microbes compete with plants for nutrients, cause disease, or produce harmful greenhouse gases. Hence, GB16_1_BI could influence plant growth predominantly by suppressing microbes and encouraged niche-specific microbes specifically involved in nitrogen cycling.

Rhizosphere

Energetics of Microbacterium thermosphactum in glucose-limited continuous culture.

Microbacterium thermosphactum was grown at 25 degrees C in glucose-limited continuous culture under aerobic (greater than 120 microM oxygen) and anaerobic (less than 0.2 microM oxygen) conditions. The end products of the anaerobic metabolism of glucose were identified as L-lactate and ethanol. Together these compounds accounted for between 85 and 90% of the glucose utilized over the full range of growth rates studied. In addition, 4% of the glucose utilized was incorporated into cellular material. Under anaerobic conditions the molar growth yield was 40 g (dry weight) of cells per mol of glucose utilized, and the maintenance energy coefficient was 0.4 mmol of glucose utilized per g (dry weight) of cells per h. For cells grown under aerobic conditions in the corresponding values were 73 g/mol and 0.2 mmol/g per h, respectively. The molar growth yield with respect to adenosine 5'-triphosphate varied with the growth rate of the culture, and the true molar growth yield with respect to adenosine 5'-triphosphate was found to be 20 g/mol of adenosine 5'-triphosphate.

Actinomycetales

[Destruction of Microbacterium lacticum, Escherichia coli and Staphylococcus aureus in milk by sprayedrying. II. Effect of drying conditions].

Bacterial death during spray drying of skim milk is essentially related to the outlet temperature of the spray drier and the type of bacteria. Under industrial spray drying conditions, survival rates of Microbacterium lacticum, Staphylococcus aureus and Escherichia coli were 50, 2, and 0.002%, respectively. These rates may vary by a 10(4) factor for outlet temperatures between 65 and 105 degrees C. No simple mathematical equation could be derived to describe the relation between bacterial death rates and outlet temperature. Our results suggest that bacterial death is due in most cases to a heating effect during the last stages of drying when the temperature of the powder particle approaches that of the air at the outlet.

Actinomycetales

[Destruction of Microbacterium lacticum, Escherichia coli and Staphylococcus aureus in milk by spray-drying. I. Selective count of surviving bacteria].

In this paper a method which allows the measure of microbial death rate during spray-drying by means of a streptomycin-resistant mutant that can be grown on a streptomycin-containing agar is described. Plate counts of Microbacterium lacticum, Escherichia coli, and Staphylococcus aureus recovered from skim milk powders were done on plate count agar in the presence and absence of streptomycin and on various selective media. The powders were produced from evaporated milk previously inoculated with those organisms. Our results showed that the proposed method allows the recovery of 78% of M. lacticum, 61% of E. coli, and 100% of S. aureus that survived spray-drying. Recoveries of surviving E. coli on violet bile agar and brilliant green bile 2% were 34% and 29% respectively. Baird-Parker and mannitol salt agar media allow the recovery of all surviving S. aureus, thus showing that S. aureus cells did not lose their ability to grow in media containig 7.5% NaCl. Our results show that physiological injury of the cells during spray-drying differs from injury due to heating only.

Actinomycetales

Isoprenoid quinones in the classification of coryneform and related bacteria.

Menaquinones were the only isoprenoid quinones found in 85 of the 95 coryneform bacteria examined. Dihydromenaquinones having nine isoprene units were the main components isolated from Corynebacterium bovis, from other glutamic acid-producing strains, and from Arthrobacter globiformis and related species. Dihydromenaquinones with eight isoprene units were found in Brevibacterium linens, the remaining Corynebacterium species and strains probably belonging to the genus Rhodococcus. Tetrahydromenaquinones with eight isoprene units were found in Arthrobacter simplex and Arthrobacter tumescens, and with nine isoprene units in Cellulomonas and Oerskovia. Kurthia and Curtobacterium were characterized by menaquinones with seven and nine isoprene units, respectively, and Microbacterium lacticum and Corynebacterium aquaticum had comparable amounts of menaquinones with 10 and 11 isoprene units. Strains received as Brevibacterium leucinophagum, Corynebacterium autotrophicum, Corynebacterium nephridii, Mycobacterium flavum, Mycoplana rubra and Protaminobacter ruber contained uniquinones as their sole isoprenoid quinones. The isoprenoid quinone data correlate well with major trends in coryneform taxonomy and are of value in the classification of coryneform and related bacteria.

Actinomycetales

Genome sequences of four bacterial strains isolated from the phyllosphere of Mangifera indica trees in the polluted tropical city of Medellín, Colombia.

Complete and draft genome sequences of four phyllosphere-associated bacterial strains (Microbacterium radiodurans, Brachybacterium rhamnosum, Sphingomonas citri, and Curtobacterium sp.) isolated from Mangifera indica leaves in polluted Medellín, Colombia, are presented. These resources enable future studies on plant-microbe interactions and phyllosphere microbial mediation of atmospheric pollutants under urban stress.

Mangifera indica

The microbiology of polony.

A survey of 25 polony samples of different brands available to the consumer in Bloemfontein showed that significant numbers of various micro-organisms were present. Aerobic micro-organisms, psychrophiles, micrococci, pseudomonads, Microbacterium thermosphactum, lactobacilli, yeasts and moulds were enumerated by the plate count technique. The mean aerobic plate count was 15,850/g and counts ranged between less than 100/g and greater than 1 million/g. Selective plate counts indicated that psychrophiles, pseudomonads and lactobacilli were the main groups present. During storage at 5 degrees C for 12 d, the mean pH of polony declined from 6,32 to 6,20 while the aerobic count increased 13 fold. Counts of all groups increased during storage at 5 degrees C especially M. thermosphactum, yeasts and moulds. No salmonellae were found and counts of Escherichia coli or Staphylococcus aureus were less than 3/g. Storage of 5 polony samples at 1.1 degrees +/- 1 degrees C until they spoilt after 8 wks resulted in the aerobic count increasing to greater than 10(8)/g. Lactobacilli and psychrophiles increased most rapidly while pH decreased from 6,20 to 5,57. Organisms isolated most frequently from spoilt polony were yeasts, micrococci, lactic acid bacteria and corynebacteria. It is concluded that standards for microbiological quality of polony are unnecessary.

Bacteriological Techniques

[Preservation of meats in a controlled atmosphere].

Commercializing meat sets problems more particularly connected with its organoleptic and microbiological qualities. As these qualities, resulting from biochemical and microbial effects, develop during the storage, the conditioning must precisely help their controlling. After examining their factors, the Author analyses the processes of conditioning which he classifies in three categories according to the techniques used and the desired finality (need to store at -1 degree C + 3 degrees C). 1. Conditioning under a steam-proof and gas pervious (O2-CO2) film. Composition of the internal atmosphere permanently close to that of the normal atmosphere. No change in the bright red colouring at the surface (oxymyoglobin). Microbial growth slowed down by refrigeration. Limited storage (a few days). Comminuted meat trade. 2. Conditioning under a totally steam--and gas--proof film. Internal atmospheric air under reduced volume and pressure ("vacuum-packed" meats). Internal changes during the storage: reduced rate O2; increased rate CO2 (cellular and microbial respirations). Surface becoming darker (absence of oxymyoglobin). Growth of the germs arrested (pathogenic and spoilage). However development of microaerophilic and acidophilic germs (in particular the lactic B.). Storage possibly extended to 8 weeks. Re-apparition of the red colour after oxygenation (opened package). Wholesale meat trade. 3. Conditioning under a film with properties close to that of (2 degrees). Initial constitution of an internal "artificial" atmosphere increased in O2 and CO2 (gas injection). No change in the bright red colouring (oxymyoglobin). Growth of the germs arrested (pathogenic and spoilage). Selection of an acidophilic aerobic flora including lactic B. and microbacterium. Storage until 12-15 days. Comminuted meat trade.

Carbon Dioxide