Previous work indicated that Streptococcus bovis HC5 had significant antibacterial activity, and even nisin-resistant S. bovis JB1 cells could be strongly inhibited. S. bovis HC5 inhibited a variety of Gram-positive bacteria and the spectrum of activity was similar to monensin, a commonly used feed additive. The crude extracts (ammonium sulfate precipitation) were inactivated by Pronase E and trypsin, but the activity was resistant to heat, proteinase K and α-chymotrypsin. Most of the antibacterial activity was cell associated, but it could be liberated by acidic NaCl (100 mM, pH 20) without significant cell lysis. When glycolysing S. bovis JB1 cells were treated with either crude or acidic NaCl extracts, intracellular potassium declined and this result indicated the antibacterial activity was mediated by a pore-forming peptide. The peptide could be purified by HPLC and matrix-assisted laser desorption ionization time-of-flight analysis indicated that it had a molecular mass of approximately 2440 Da. The terminal amino acid sequence was VGXRYASXPGXSWKYVXF. The unnamed amino acid residues (designated by X) had approximately the same position as dehydroalanines found in some lantibiotics, but samples that were reduced and alkylated prior to Edman degradation did not have cysteine residues. The only other bacteriocin that had significant similarity was the lantibiotic precursor of Streptococcus pyogenes SF370, but the identity was only 55 %. Based on these results, the bacteriocin of S. bovis HC5 appears to be novel and the authors now designate it as bovicin HC5.

Mattacin is a nonribosomally synthesized, decapeptide antibiotic produced by Paenibacillus kobensis M. The producing strain was isolated from a soil/manure sample and identified using 16 S rRNA sequence homology along with chemical and morphological characterization. An efficient production and isolation procedure was developed to afford pure mattacin. Structure elucidation using a combination of chemical degradation, multidimensional NMR studies (COSY, HMBC, HMQC, ROESY), and mass spectrometric (MALDI MS/MS) analyses showed that mattacin is identical to polymyxin M, an uncommon antibiotic reported previously in certain Bacillus species by Russian investigators. Mattacin (polymyxin M) is cyclic and possesses an amide linkage between the C-terminal threonine and the side chain amino group of the diaminobutyric acid residue at position 4. It contains an (S)-6-methyloctanoic acid moiety attached as an amide at the N-terminal amino group, one D-leucine, six L-␣,␥-diaminobutyric acid, and three L-threonine residues. Transfer NOE experiments on the conformational preferences of mattacin when bound to lipid A and microcalorimetry studies on binding to lipopolysaccharide showed that its behavior was very similar to that observed in previous studies of polymyxin B (a commercial antibiotic), suggesting an identical mechanism of action. It was capable of inhibiting the growth of a wide variety of Gram-positive and Gramnegative bacteria, including several human and plant pathogens with activity comparable with purified polymyxin B. The biosynthesis of mattacin was also examined briefly using transpositional mutagenesis by which 10 production mutants were obtained, revealing a set of genes involved in production.

Root-knot nematodes (Meloidogyne spp.), which cause severe global agricultural losses, can establish a special niche in the root vascular cylinder of crops, making them difficult to control. Endophytic bacteria have great potential as biocontrol organisms against Meloidogyne incognita. Three endophytic bacteria were isolated from plant tissues and showed high nematicidal activity against M. incognita second-stage juveniles (J2) in vitro. The gyrB gene sequence amplification results indicated that the three isolates were Bacillus cereus BCM2, B. cereus SZ5, and B. altitudinis CCM7. The isolates colonized tomato roots rapidly and stably during the colonization dynamic experiment. Three pot experiments were designed to determine the potential of three endophytic bacterial isolates on control of root-knot nematodes. The results showed that the preinoculated B. cereus BCM2 experiment significantly reduced gall and egg mass indexes. The inhibition ratio of gall and egg mass was up to 81.2 and 75.6% on tomato roots and significantly enhanced shoot length and fresh weight. The other two experiments with inoculated endophytic bacteria and M. incognita at the same time or after morbidity had lower inhibition ratios compared with the preinoculated endophytic bacteria experiment. The confocal laser-scanning microscopy method was used to further study the possible mechanism of endophytic bacteria in the biocontrol process. The results showed the localization pattern of the endophytic bacteria B. cereus BCM2-(str′)-pBCgfp-1 in tomato root tissues. Root tissue colonized by endophytic bacteria repelled M. incognita J2 infection compared with the untreated control in a repellence experiment. We isolated an endophytic B. cereus strain that stably colonized tomato and controlled M. incognita effectively. This strain has potential for plant growth promotion, successful ecological niche occupation, and M. incognita J2 repellent action induction. It plays an important role in endophytic bacteria against root-knot nematodes.

The maximum carboxylation rate (Vcmax) is a key parameter in determining the plant photosynthesis rate per unit leaf area. However, most terrestrial biosphere models currently treat Vcmax as constants changing only with plant functional types, leading to large uncertainties in modeled carbon fluxes. Vcmax is tightly linked with Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco). Here we investigated the relationship between leaf chlorophyll and Rubisco (Chl‐Rub) contents within a winter wheat paddock. With chlorophyll as a proxy of Rubisco, a semimechanistic model was developed to model Vcmax25 (Vcmax normalized to 25°C). The Chl‐Rub relationship was validated using measurements in a temperate mixed deciduous forest in Canada. The results showed that Rubisco was strongly correlated with chlorophyll (R2 = 0.96, p < 0.001) for winter wheat since the absorption of light energy by chlorophyll and the amount of CO2 catalyzed by Rubisco are tightly coupled. Incorporating the Chl‐Rub relationship into the semimechanistic model, the root mean square error of modeled Vcmax25 was the lowest among all estimation models. The slopes of Chl‐Rub relations were almost consistent in the winter wheat and temperate forest, demonstrating the potential for using leaf chlorophyll content as a proxy of leaf Rubisco in modeling Vcmax25 at large spatial scales. We anticipate that improving Vcmax25 estimates over time and space will reduce uncertainties in global carbon budgets simulated by terrestrial biosphere models.