Current Microbiology

The treatment of infections caused by bacteria resistant to the vast majority of antibiotics is a challenge worldwide. To evaluate the effect of S-thanatin (an analog of thanatin, a cationic antimicrobial peptide isolated from the hemipteran insect Podisus maculiventris) against microbial resistant to antibiotics, we studied its bactericidal kinetics, synergistic effect, resistance, and activity on clinical isolates of Klebsiella pneumoniae resistant to conventional antibiotics with different structures. The bactericidal rate of S-thanatin was more than 99% against K. pneumoniae ATCC 700603 when bacterial cultures were monitored for 60 min. The peptide was synergistic with β-lactam cefepime in most of the clinical MDR isolates tested (7/8). An average value of FIC was 0.3708. No synergy was found between the peptide and amoxicillin, gentamycin, tetracycline, or ciprofloxacin in all bacteria tested. A total of 48 isolates of K. pneumoniae with different resistance spectrum tested was susceptible to S-thanatin. The MICs were 6.25–25 μg/ml. No significant difference in the MICs of S-thanatin between the sensitive isolates and the resistant isolates to single antibiotic was observed (P > 0.05). The resistance of K. pneumoniae ATCC 700603 to S-thanatin was slightly higher, when cultured at sub-inhibitory concentration for 5 days. S-thanatin may be an attractive candidate for developing into an antimicrobial agent.

Yeasts play an important role in cheese making, by contributing to microbial community establishment and improving flavor. This study aimed at investigating the impact of NaCl and temperature on growth and survival of 20 strains belonging to the yeast species Candida intermedia (2 strains), Debaryomyces hansenii (11), Kluyveromyces lactis (1), Papiliotrema flavescens (1), Rhodotorula glutinis (1), Sterigmatomyces halophilus (2) and Yamadazyma triangularis (2) isolated from Danish cheese brines. All yeasts could grow in Malt Yeast Glucose Peptone (MYGP) medium with low NaCl (≤ 4%, w/v) concentrations at 25 °C and 16 °C. Further, none of the strains, except for one strain of D. hansenii (KU-9), were able to grow under a condition mimicking cheese brine (MYGP with 23% (w/v) NaCl and 6.3 g/L lactate) at 25 °C, while all yeasts could grow at 16 °C, except for the two strains of C. intermedia. In the survival experiment, D. hansenii, S. halophilus and Y. triangularis survived in MYGP with 23% (w/v) NaCl throughout 13.5 days at 25 °C, with Y. triangularis and S. halophilus being the most NaCl tolerant, while the remaining yeasts survived for less than 7 days. These results enable the selection of relevant yeasts from cheese brines for potential use in the cheese industry.

Parasporal inclusion protein of Bacillus thuringiensis-LDC-501 (Bt-LDC-501) exhibits selective cytocidal action towards human colon cancer cells. The yield of this parasporal protein was minimum in the normal culture. In order to increase the yield of protein from Bt-LDC-501 various agro-based cost-efficient nutrient sources such as corn steep liquor (CSL), sesame oil cake extract (SOC), groundnut oil cake extract (GOC), neem oil cake extract (NOC), rice bran extract (RB), wheat bran extract (WB), red gram hull extract (RGH), green gram hull extract (GGH), black gram hull extract (BGH), Mysore gram hull extract (MGH), and maize flour waste extract (MFW) were screened. Statistical experimental designs such as Plackett–Burman design (PBD) and response surface methodology (RSM) were the tools employed for the optimization of medium. Groundnut cake extract (GOC) served as a potential carbon and nitrogen source, as it induced twofold higher production of parasporal protein. Among the optimized seven media components KH2PO4, K2HPO4, GOC, NaCl, MgSO4, MnSO4, and FeSO4, the concentrations of GOC, NaCl, and MgSO4 have significant effect on parasporin production as well as cytotoxicity against colon cancer cell line, HCT-116. Bt-LDC-501 was found to produce 0.88 mg/ml of parasporal protein in optimized medium. In the un-optimized medium, the yield was 0.23 mg/ml only. This indicated that there was 382% of increase in the production of Parasporal protein. Parasporin protein with the molecular weight of 27 kDa has been purified with the purification fold of 27.1. It showed a LC50 value of 0.91 and 1.21 µg/ml against colorectal cancer cell lines such as HCT-116 and HCT-15, respectively. Purified parasporin exhibited stable cytocidal activity between pH 4.0 and 9.0 at room temperature. The present study revealed that the quantity and quality of media composition were necessary for eliciting cytocidal activity against human colon cancer and the importance of alternate cost-effective production of clinically significant parasporin. Moreover, this is the first report regarding optimization of media components for parasporal protein production from Bt.

In E. coli, chemotactic behavior exhibits perfect adaptation that is robust to changes in the intracellular concentration of the chemotactic proteins, such as CheR and CheB. However, the robustness of the perfect adaptation does not explicitly imply a robust chemotactic response. Previous studies on the robustness of the chemotactic response relied on swarming assays, which can be confounded by processes besides chemotaxis, such as cellular growth and depletion of nutrients. Here, using a high-throughput capillary assay that eliminates the effects of growth, we experimentally studied how the chemotactic response depends on the relative concentration of the chemotactic proteins. We simultaneously measured both the chemotactic response of E. coli cells to l-aspartate and the concentrations of YFP-CheR and CheB-CFP fusion proteins. We found that the chemotactic response is fine-tuned to a specific ratio of [CheR]/[CheB] with a maximum response comparable to the chemotactic response of wild-type behavior. In contrast to adaptation in chemotaxis, that is robust and exact, capillary assays revealed that the chemotactic response in swimming bacteria is fined-tuned to wild-type level of the [CheR]/[CheB] ratio.

Rice, a staple food crop worldwide, suffers devastating yield losses as a result of blast disease caused by Magnaporthe oryzae Cav. The adverse effects of chemicals on the environment are rising concerns for sustainable and eco-friendly approaches. The use of antagonistic microbes for the management of rice blast appears to be a sustainable solution to this challenge. Herein, we isolated 20 Streptomyces strains from rice rhizosphere, among which the isolate STR-2 exhibited maximum inhibition of mycelial growth of M. oryzae accounting for 50% reduction over control. The isolate STR-2 was identified as S. chrestomyceticus through 16S rRNA gene sequencing. In vitro tests demonstrated its ability to produce antifungal and bioactive compounds and also synthesize siderophore, IAA, and phosphate-solubilizing agents, thereby promoting plant growth upon inoculation on rice seeds. GC–MS analysis showed the presence of volatiles, antifungal, antimicrobial, and antioxidant compounds with different retention times. The crude antibiotic extract of 0.5% of S. chrestomyceticus STR-2 reduced the mycelial growth of M. oryzae over the control. Application of talc-based formulation of Streptomyces chrestomyceticus STR-2 resulted in the least disease incidence (15.89%) with the highest disease reduction of 65.26% over untreated control under field condition. These findings indicate the potential of S. chrestomyceticus as a potential bio-inoculant against rice blast disease.

Cyanobacteria produce some carotenoids. We identified the molecular structures, including the stereochemistry, of all the carotenoids in the terrestrial cyanobacterium, Nostoc commune NIES-24 (IAM M-13). The major carotenoid was β-carotene. Its hydroxyl derivatives were (3R)-β-cryptoxanthin, (3R,3′R)-zeaxanthin, (2R,3R,3′R)-caloxanthin, and (2R,3R,2′R,3′R)-nostoxanthin, and its keto derivatives were echinenone and canthaxanthin. The unique myxol glycosides were (3R,2′S)-myxol 2′-fucoside and (2R,3R,2′S)-2-hydroxymyxol 2′-fucoside. This is only the second species found to contain 2-hydroxymyxol. We propose possible carotenogenesis pathways based on our identification of the carotenoids: the hydroxyl pathway produced nostoxanthin via zeaxanthin from β-carotene, the keto pathway produced canthaxanthin from β-carotene, and the myxol pathway produced 2-hydroxymyxol 2′-fucoside via myxol 2′-fucoside. This cyanobacterium was found to contain many kinds of carotenoids and also displayed many carotenogenesis pathways, while other cyanobacteria lack some carotenoids and a part of carotenogenesis pathways compared with this cyanobacterium.

A marine mesophilic, irregular coccoid methanogen, which shows close resemblance toMethanococcus sp., was isolated from the biofilm of shiphulls docked in Los Angeles harbor. Hydrogen plus carbon dioxide or formate served as substrates for methanogenesis in a mineral salt medium. The isolate did not use acetate and methanol as sole source of carbon and energy. The organism had an optimal pH range of 6.8–7.0 and a temperature optimum of 37°C. Elevated levels of sodium chloride were required for optimum growth. Optimum levels of total sulfide and magnesium chloride for growth were 1.0mm and 10mm respectively. The isolate used ammonia as nitrogen source. The concentration of 30mm ammonium chloride supported maximum growth of the isolate.

Four phages infectious to Mesorhizobium strains were identified in soil samples taken from local Robinia pseudoacacia stands. Based on their polyhedral heads and short noncontractile tails, three of the phages, Mlo30, Mam12, and Mam20, were assigned to group C of Bradley’s classification, the Podoviridae family, while phage Mlo1, with its elongated hexagonal head and a long flexible tail represented subgroup B2 bacteriophages, the Siphoviridae family. The phages were homogeneous in respect of their virulence, as they only lysed Mesorhizobium strains, but did not affect strains of Rhizobium or Bradyrhizobium. On the basis of one-step growth experiments, the average virus yield was calculated as approximately 10–25 phage particles for phages Mlo30, Mam12 and Mam20, and as many as 100–120 for phage Mlo1. The rate of phage adsorption to heat-treated cells showed differences in the nature of their receptors, which seemed to be thermal sensitive, thermal resistant, or a combination of the two. Only the receptor for phage Mlo30 was likely to be an LPS molecule, which was supported by a neutralization test. The smooth LPS with O-antigenic chains of the phage-sensitive M. loti strain completely reduced the bactericidal activity of virions at a concentration of 1 μg/ml. The molecular weights of phage DNAs estimated from restriction endonuclease cleavage patterns were in the range from ~39 kb for group C phages to ~80 kb for B2.